ROOM ACOUSTICS SPECIAL,ISSUE

• Computet Simulation

• Sabine Rooms

Australian Acoustical Society

• Neural ,Networks

• Office Acoustics

Vol. 23 No.3 December 1995

Yoor PC

+

Here's What it Does:• TmnsientCaptureandFFT• Linear andPower Spectrum• Synchronous Average• RPM based Spectral Analysis• Runup and Coastdown Waterfalls• Order Tracking• Transfer Function andCoherence• Realtime Zoom• Correlation• DemodulationandHilbert Transform• Stepped SineTransfer Function• AcousticIntensity• RealtimeV-i Octave Analysis• Shock Response Spectrum• DiskRecord andPlayback• Closed Loop Shaker Control• 1to 16ADCInput Channels

• Multiple DACOutput Channels

AnyPC-desO.!OPOf pcrt.llIe-c.., be II'l nslllfftled llIlO.D'III'hy$lCSlWK_mkoaly~. (....., . _ Iloo. .........•n" NI'S'lIfI IKJ.". lhrs!:omiwQ 4!I6cllloflJE govftyOlll lo9"l.pOfUblejMt,~m.nt

One Dynami c Instrument

Ant-" , proteet!'llII ilCAllCsand"",,," 'llM 'll DSPprOClKloQI'SfofllllM

10000lr>on01 lIlIl...- ffT.......

The DP410FFTAnalvzer ;s fast becomingtheinstrument ofchoicefordrnamics solutions.

~fitjj

EDITORIALCOMM.,."~liaNeville FletcherMarion BurgessJosephLai

ASSISTING EDITOR:LeighKenna

Vol 23 No3

ARTICLES

CONTENTS December 1995

BUSINESS MANAGER:MrsLeighWallbank

ForAll GeneralBusiness(subscriptions, extracopies, back

issues,advertising,etc.)

MrsLeighWallbankPOBox579CRONULLANSW2230'Tel (02)5284362Fax(02)5239637

ForAll EditorialMatters(articles, reports, news, bookreviews,

newproducls,etc)

TheEditor,AcousticsAustraliaAcoustics &Vibration CentreAustralian Defence ForceAcademyCANBERRA ACT2600Tel (06)2688241Fax(06)2688276email:m-burgess@adfa.oz.au

AcousticsAustraliaispublishedbylheAuslralianAcousticaiSociety(A.C.N.OOO712658)

Responsibility lor thecontents ofarticlesrests upon the authors and not theAustralian Acoustical Society. Articlesarecopyright,butmaybereproducedinfullprovided adequate reference isquol­ed.AcousticsAustraliaisabstracledandindexed in Engineering Index, PhysicsAbstracts, Acoustics Abstracts & Noise:Abstracts,Reviews.

Printed byCronulla Printing CoPtyLtd,16CronullaPlaza,CRONULLA2230Tel (02)5235954,Fax(02)5239637

ISSN0814-6039

Computer Simulation Techniques for Acoustical Design of RoomsJHRlndel 81

Predicting the Acoustics of Concert Halls Using an ArtificalNeural NetworkF Fricke and C Hoon Haan 87

Some Notes on Sabine RoomsDABles 97

Notes on Office AcousticsBMurray 105

Diary ....

Acoustics Australia Informalion .....

AustralianAcousticaISocie1ylnformation ...

COVER:Reflection of spherical waves from straight edge object- see article by Zhu and McKerrow.

Vol. 23 (1995) No.3 - 77

AUSTRALIAN ACOUSTICAL SOCIETY

SUSTAINING MEMBERSASSDelAnoN Of AUSTRAUANAcousnCALCOHSULTANTSSCIENCE CENTRE FOUNDATIONPRlVATEBAG1.DAALlNGIiJRST2010

ASSOClAnOHOfNOISECOfmIOL ENGINEERINGP,O,BOX484MT.EUZA3930

BARClAYENGINEERlHG12·16 CATAlANORO.CANNINilVAl..f61S5

BHPSTEEL,SKEETaCOILPRODUCTS DIVISIONPOBOXn,PORTKEI.lBLA25OIS

BlLSOMAUSTlIAUAPTY lTD19TEPKO ROAD,TEARYHIu.s2OEl4

BORALPLASTEABOARD616LOOIMERST. -,PORTMELBOURNE 3207 •

BRUEL&KJAfRAUSTRALlAPTY LTDPO90Xm.TfMEYHIUS:z0B,6CHAOWICKTECHNOlOGY9COOK STAEET,F~STVILLE2OEl7

CSRQYPROCK & BRADFORDINSULATIONLEVEL5,9 HELP STREETCHATSWOOD 2067eMONA1NSTAUMENTS Pt\.86PARRAMATTAROAOCAMPEROOWN 2050ENVlROHMOOALNOISECONlROLP,lSOAJVERSDERQAOO!IPPIHGtKlRTON2170

GP EMBELTOfol&COPTYLTDt41-1049BAKERS ROAOcoeURC33058INC COAPORATlONPTYlTO22Cl£ElANDROAOOAKLEIGH SCUTH3167JOYCEAUSTllAUASo9BRIDGERQAO,MOOREB.l.NK211O

NAPSlLEHTfLOseEllJCKl.At.OST,Q.AYTON3168

P!A CEENGINEERI'«;P TYLTtI2I2O t.lARlGOlOSTAEVESBY2212

ADeLACOMPOSITEPRODUCTS73-105FRANKSTOtHIANDE~NG RD.DANDENONa3175

SAFElYEOUPWENT AUSTRALlA.Pi\.35/1-3JUBll EEAVI:.

WARRIEWOOD 2102

PVRonK PTYLTD1.7 UAGOWAR 1'10,GIRRAWEEN214.5

WARBURTON FRANKlOMsion01een·IRH IMdustnes Pf)'Ud1<10 BUFl'NOODHIGHWAYBUAlflOOO3125

WOFlKCOVEFlACOUSTICS132 LONDONDERRY1'1 0LONOONDeARY2753

~fEE3:9pt, [0315>S1271r.. «()3j!65 f956

_s...... WaIOS/4ClPll102I148050l4r.. /02114810 16

78 · Vol. 23 (1995) No_3

QuHMlnPII10118011 455Sr" 10118ol14600.....olemAoot"' ...,­~le ee1(r....

r.. jO.lIY.b1956

Soolll _ . /ffllOBI3651ooor" (Il8j36!>lOOl

Acousuca Australla

It is now j us t 100 years s ince thePrcsidentofHarvardUnivcr1ity dire<:ledWal1acc Clement Sabine, then a youngASlIislanl Professor (i.e . Lect urer) inphysics 10 " propose changes forremed ying the acoustical diff iculties inthe reerore-recm of the Fogg ArtMuseum , I bui lding that had just beencom pleted" How famil iar those wordssound to the mod ern acous ticalconsultan t! ln the course of remedy ingthose "di ffi cullies~, Sabine establ ishedthe modem sci enc e of archi tectu ra lacoustics. It is pleas ing 10 record thatHarvard recognise d his con tribu tion sand later conferred on him an honoraryDoctcrate of Sclence c he had no PhD ·and made him the first Dean of the newGraduate Schoo l of Appl ied Science.

In his first published pape r in 1898,Sabine wrote: " In order tha t heari ng maybe geed in any auditorium, it isnecessary that the sound should besuffie iet1tly loud; that the simultan eouscomponern s of a compl ex sound shou ldmaintain their proper relative intens it ies;and that lhc success ive sounds in rapidl ymoving art iculation, either in speec h ormusic, should be clear and distinc t, free

from each other and from extraneousnoises." These criteria cou ld hardly beexpressed better today, a century later.With only the simplest equipment ­remember that microphones and valveamplifien had nOIyet been invented- hewenl on 10 eslablish his famous law forreverbera tion lime as a function ofvolume and surfaceab'lOrption, andlaterwent on 10 measure Ihe absorpti onfaetOl'1l for many materials and surfaces,u well as trans mission losses and manyotber properti es of practical inte restHis papers were published. for the mostpart , in architectural and tec hni caljou rnal s rather than in the scientif icluerarure, so Ihat they would bcavai lableto membcn of the profess ion.

Sab ine 's experimenta l work Will

mct iculous, and it was said that he " wasreluctant to publish the results of ancxperi ment until he was sure it had beendone 50 well that nobody would everneed to repeat il." Conseq uently thevolume of his publications is not verylarge. though it includes such innovativelechn iques Ii the vis ualisat ion ofaco uslic wavefro nts usi ng sparkpholography in small -scale models. He

did, however, leave also a memorablecollection of buildings for which hecontributed the acousli c design. The

best known of these is Symphony Hall inBoslon,of'C nedin 1890 and still widelyregarded as one of the world's greatconcert hall s, &8 well as Ihe first 10 bedesi iJ:nedusingquanlir ative acou slicprincip les. He laler went on to designthe acoustics of many well known

buildings, ineluding the Caehedral of StJohn the Divine in I\ ew York, wh ich isthe largest Gol hic cathe dral in the world

The subjeCI has . of course,

progressed I great deal since Sabin e'stime, but his fundam ental insights still

sland. In th is issue, our contrib utors

show how modern techn iques of

mathem atical analy si s and comp uter

modelling can give us both an improvedunders tand ing of lheacousliepropertiesof halls and a set of tools not only forimproving the acou~tics or e~ i sling hallsbut , even mor e importan tly, foropt imizing in advance Ihe performanc eof halls thai are'still in the design stage.

NevjlfeFll'lchl' r

COUNCIL OF THE AUSTRALIAN ACOUSTICAL SOCIETY

PresidentVice-PresidentTreasu rerGene ral SecretaryFederal RegistrarCha irman, Sianding Commillee on Membershi p

Arch ivist

Councillors

NProf Charles DonDr Graema YatesMr Peter HeinzeMr David WatkinsMr Ray PiesseMr Ken CookMr David Watkins

Ne w So uth Wi les Quee nsl l nd

Dr Norman Carter Mr Russell Brown

Dr Stephen Samuels Mr Ross Palmer

scoosrcsAustra lia

South Australia

Mr Peter He inze

Mr Byron Martin

Victor ia

A/Prof Charl e s Don

Mr Claudlo Senese

We .temAUltral ia

MrNorbert Gabr ie ls

DrGraeme Yates

Vol 23 (1995) No, 3-79

NO NONSENSECONTROL OF

ENTERTAINMENT NOISEIN

FUNCTION & ENTE RTAINME NTVENUES

~ilONT!ECC"lC>

Programmable Noise Monitor(previoosly known as Gax om 2376)

Simply dial up the Tl;'l uired Sound Threshold

• Trigger Range 60 to 120DB

• Weighting: Linea r, A or Low Pass Filter

Visual Display Unit indicates approaching Thre shold

• Controls ;n lockable Stee1 Cabinet

Matrix Industries Ply . Ltd. patented wall tiesprovide structural support while reducingtransmission of structure borne vibrationsResilient mount ing systems are avai lable for allmasonry and plasterboard walls and lightweightf1oatingftoors.

Matrix Industries products are reduc ing noise instudios and theatres throughout AustraliaEnq\l~;es and Sakol;

MATRIX INDUSTRIES PTY LTD3 RICHAROSON STREET, TAREE NSW 2430

PH/f AX: (065 ) 522 206AlsoDisj, jbuled by

BRUNSWICK SALES PTY. LTD.49 LEICESTER STREE T, FITZR OY VIC 306 5

Ph : (03) 9419 0099 Fax (03) 9419 2218

~A(U·Vl8 fledron'csA c o u ,I i c g n d V i b r o l i 0 n E I e c l r on i e ,

Calihralionrepa.lr]acillll&J

• Sound Level Meters & Filters

• Noise Dose M eters

• Calibrators & Pistonphones

• N o ise Logger s & N oise Analy ze rs

56AThomf"O'lS,_Dn.",~."..,NSW2047

T.~ G18 470 179Tdif.. , (02) 819 6N8

POIloxW16W......., h. , NSW 1046

I;or much less th.m

anywhere else

AaJ-VlBEIectronicscan helpyou with

calibration. repair or

hire of instrumenls

supplie<l bydiflerent

manufacturers.

\Ve also trade in new

and used instruments

an d ac{·esso ries

Se nd it to ACU-ViB Electronics. \Vith no do ubt the best in the field o f Acoustic an d Vibr ation s

Vol. 23 (1995) no . 3

ComputerSimulation Techniques for AcousticalDesign of Rooms

Jens Holger RindelThe Acoustics LaboratoryTechnical UnIversity of DenmarkDK-2800 Lyngby, Denmark

Abstract: After decades of development room acoustical computer models have matured. Hybrid methodscombine the best features from image source models and ray tracing methods and have lead to significantlyreduced calculationtimes. Due to the wavenatureof soundit has been necessaryto simulatescattering effects inthe models. Today'sroom acousticalcomputermodels haveseveral advantagescomparedto scale models. Theyhave become reliable and efficient design tools for acoustic consultants, and the results ofa simulation can bepresentednot only for the eyes but also for the ears with new techniques for auralisation.

1. INTRODUCTIONIn acoustics as in many other areas of physics a basic questionis whether the phenomena should be described by particles orby waves. A wave model for sound propagation leads to moreor less efficient methods for solving the wave equation, likethe Finite Element Method (FEM) and the Boundary ElementMethod (BEM). Wave models are characterized by creatingvery accurate results at single frequencies, in fact too accurateto be useful in relation to architectural environments, whereresults in octave bands are usually preferred. Another problemis that the number of natural modes in a room increasesapproximately with the third power of the frequency, whichmeans that for practical use wave models are typicallyrestricted to low frequencies and small rooms, so thesemethods are not considered in the following.

Another possibility isto describe the sound propagation bysound particles moving around along sound rays. Such ageometrical model is well suited for sound at high frequenciesand the study of interference with large, complicatedstructures. For the simulation of sound in large rooms thereare two classical geometrical methods, namely the RayTracing Method and the Image Source Method. Forbothmethods it is a problem that the wavelength or the frequencyof the sound is not inherent in the model. This means that thegeometrical models tend to create high order reflections whichare much more precise than would be possible with a realsound wave. So, the pure geometrical models should belimited to relatively low order reflections and some kind ofstatistical approach should be introduced in order to modelhigher order reflections. One way of introducing the wavenature of sound into geometrical models is by assigning ascattering coefficient to each surface. In this way the

Acoustics Australia

reflection from a surface can be modified from a pure specularbehaviour into a more or less diffuse behaviour, which hasproven to be essential for the development of computermodels that can create reliable results.

2. SIMULATION OF SOUND IN ROOMS

2.1 The Ray Tracing Method

The Ray Tracing Method uses a large number of particles,which are emitted in various directions from a source point.The particles are traced around the room losing energy at eachreflection according to the absorption coefficient of thesurface. When a particle hits a surface it is reflected, whichmeans that a new direction of propagation is determinedaccording to Snell's law as known from geometrical optics.This is called a specular reflection. In order to obtain acalculation result related to a specific receiver position it isnecessary either to define an area or a volume around thereceiver in order to catch the particles when travelling by, orthe sound rays may be considered the axis ofawedge orpyramid. In any case there is a risk of collecting falsereflections and that some possible reflection paths are notfound. There is a reasonably high probability that a ray willdiscover a surface. with the area A after having travelled thetime t if the area of the wave front per ray is not larger thanA12. This leads to the minimum ;umber of rays N

N;"BJ!'C t2 (1)A

where c is the speed of sound in air. According to this equationa very large number of rays is necessary fora typical room.As an example a surface area ofl0 m- and a propagation timeup to only 600 ms lead to around 100,000 rays as a minimum.

Vol. 23 (1995) NO.3 - 81

The development of room acoustical ray tracing modelsstarted some thirty years ago but the first models were mainlymeant to give plots for visual inspection of the distribution ofreflections [I]. The method was further developed [2],andinorder to calculate a point response the rays were transferredinto circular cones with special density functions, whichshould compensate for the overlap between neighbouringcones [3]. However,itwasnotpossibletoobtainareasonableaccuracy with this technique. Recently, ray tracing modelshave been developed that use triangular pyramids instead ofcircular cones [4], and this may be a way to overcome theproblem of overlapping cones.

2.2 The Image Source MethodThe Image Source Method is based on the principle that aspecular reflection can be constructed geometrically bymirroring the source in the plane of the reflecting surface. Ina rectangular box shaped room it is very simple to constructall image sources up to a certain order of reflection, and fromthis it can be deduced that if the volume of the room is V,theapproximate number of image sources within a radius of ct is

Nref=4;;3

(3 (2)

This is an estimate of the number of reflections that will arriveat a receiver up to the time t after sound emission, andstatisticallythise~uationholdsforanyroomgeometry. Inatypical auditorium there is often a higher density of earlyreflections, but this will be compensated by fewer latereflections, so on average the number of reflections increaseswith time in the third power according to (2).

The advantage of the image source method is that it is veryaccurate, but if the room is not a simple rectangular box thereis a problem. Withn surfaces there will be n possible imagesourcesoffirstorderandeachofthesecancreate(n-l)second order image sources. Up to the reflection order i thenumber of possible image sources Nso" will be

N sou -1+ (n ~ 2)[(n-l)i -I]-(n-I/. (3)

As an example we consider a 1,500 m3 room modelled by 30surfaces. The mean free path will be around 16 m whichmeans that in order to calculate reflections up to 600 msareflectionorderofi= 13 is needed. Thus equation (3) showsthat the number of possible image sources is approximatelyN sou =2913 _I01~ The calculations explode because of theexponential increase with reflection order. If a specificreceiver position is considered it turns out that most of theimage sources do not contribute reflections, so most of thecalculation efforts will be in vain. From equation (2) itappears that less than 2500 of the 10 19imagesourcesarevalid

fora specific receiver. For this reason image source modelsare only used for simple rectangular rooms or in such caseswhere low order reflections are sufficient, e.g. for design ofloudspeaker systems in non-reverberant enclosures [5,6].

2.3 The Hybrid MethodsThe disadvantages of the two classical methods have led todevelopment of hybrid models, which combine the best

82 - Vol. 23 (1995) NO.3

features of both methods [7,8,9]. The idea is that an efficientway to find image sources having high probabilities of beingvalid is to trace rays from the source and note the surfaces theyhit. The reflection sequences thus generated arc then tested asto whether they give a contribution at the chosen receiverposition. This is called a visibility test and it can be performedas a tracing back from the receiver towards the image source.This leads to a sequence of reflections which must be thereverse of the sequence of reflecting walls creating the imagesource. Once 'backtracing' has found an image to be valid,then the level of the corresponding reflection is simply theproduct of the energy reflection coefficients of the wallsinvolved and the level of the source in the relevant direction ofradiation. The arrival time of the reflection is given by thedistance to the image source.

It is, of course, common for more than one ray to follow

the same sequence of surfaces, and discover the samepotentially valid images. It is necessary to ensure that each

valid image is only accepted once, otherwise duplicatereflections would appear in the reflectogram and cause errors.Therefore it is necessary to keep track of the early reflectionimages found, by building an 'image tree'.

For a given image source to be discovered, it is necessary

for at least one ray to follow the sequence which defines it.The finite number of rays used places an upper limit on thelength of accurate reflectogram obtainable. Thereafter, some

other method has to be used to generate a reverberation tail.This part of the task is the focus of much effort, and numerous

approaches have been suggested, usually based on statisticalproperties of the room's geometry and absorption. One

method, which has proven to be efficient, is the 'secondarysource' method used in the ODEON program [9]. Thismethod is outlined in the following.

After the transition from early to late reflections, the rays

are treated as transporters of energy rather than explorers ofthe geometry. Each time a ray hits a surface, a secondary

source is generated at the collision point. The energy of thesecondary source is the total energy of the primary sourcedivided by the number of rays and multiplied by the reflection

coefficients of the surfaces involved in the ray's history up to

that point. Each secondary source is considered to radiate intoa hemisphere as an elemental area radiator. Thus the intensityis proportional to the cosine of the angle between the surfacenormal and the vector from the secondary source to the

receiver. The intensity of the reflection at the receiver alsofalls according to the inverse square law, with the secondary

source position as the origin. The time ofarrival of a reflectionis determined by the sum of the path lengths from the primary

source to the secondary source via intermediate reflectingsurfaces and the distance from the secondary source to the

receiver. As for the early reflections a visibility test is made

to ensure that a secondary source only contributes a reflectionifit is visible from the receiver. Thus the late reflections arespecific to a certain receiver position and it is possible totake

shielding and convex room shapes into account.

Acoustics Australia

Figun: I.Princ:iplc of . hybrid modeLT ""l oound!a)'l CTUteimo,e IOWUJ ror c..ty rd «tioru IfId _onduy IOILR:.. 0111hc:u11,forlllerdlcctiOll'-

Figure 1 illustratts in tchematic fonn how the u.kulsliOl'lmodel beh..·u In the figure. !Wl) neighbouri"i nyt arefoll~uplolhesilllh.reflectionordeT.Thetralllilionorder

is~ 10 2, so abcJ,;c!his onXr the ny" reflection dirttrionsare ebosca al randomfrom. di.sllibulion foll_ing Lambm i!aw(_ laln). The flt'tll_renectionll arespccular,aftdboth1'1)" rind the imllj:e sources $ 1and 5 11, Thew image IlCJW1;CSgiveriSCIOOllereneclioncachintheresponsc, sincctheym:visible from the receiver pomeR. In . more oornpliC1ttd room!hilmiShlnolbctruefor.l1 imagelOU1CC$.Thc:oonllibutionsfrom5, 51 and 5 1l arrive .1 \he KUivcr at limes propoctional10 !heir distanen from the rcceivn. Abo'.-e onkr 1, Ck h raygmentu indo:pc'ndcnl J«Ofldary IlCJW1;Cslinuttd DO the

rd lo.:l in, . urfaces. In the simple boI-wped room thne arc:.11 visible from Ihc receiv er, .nd thus !hey . 11 Jiveeonllibut ions 10 thc: rnportK. In Figure 2 is displayed theresponse idcnlif'ying the contributions from the sourcc , tile

two irn' Ke lOUfCcs and the c ighl secondary lOVJ'CuIn . comple1culcul'lion lhe las learlyref\c:ction(fToma n

im.g e l.Ourte ) will typ icallyarrivc afterthefirsll ale rcnect ion(from . !lCtondary source), $0 there will be. time intervalwhere the two melhods over lap. Thi s il indicated on thecalculated energy resp onse curve in Figure 3. Also shown isthe reverse-inte gr ated decay curve, whic h i, used forc. lculalion ofl'Cllerocralion time and other room acoos licalparameters.

In lhe hybrid modcl describcd .bove il is.aitiCIl point at

...1tich rcflcdion order the traIIsition is made from early to II-Ierencdions. Since the earl y reflmions are delCTlnined moreKCUralelylhanthc la\( retkctiOll$oncmigblthinkwlbettn'

1Ei~'

~T_SS, S••• b c d e f l b

Fe- 2 ketloaoco- b''''~ P. ill F'Fft I.

Fi, ure 3. tYPicl-limpulse n sporlse(energy) and decl-~ Cu. ....calcutltedwilh lhybri dmodol

results arc obt.J.incd with the transition order II hi~h I-~

possible . H<M'eVCf . for I- givcn nurnber of rays the clwlc r ofmiw"i some iml.gcs incruses with reflection order and ....iththe nwn bcr of VIl.11s..n~s in the room . This ",UC'olI tNtthe number ofnlys should beas luge u possible , hmi lrd onlybyp-lienccl.lldcompu>crupacity. H~.tbc:n: are 1llo'O

lhinKs w1tich ml-ke lhlS con clusion wron g. Flnlly. !he

=y.:~ ~i::eo~~ s~~:'''~nt;I-~:'':gencral ioct, 50 the number of n:fl~tions minrd dlle 10in$llfflCiefd 111)" will be much f('\O'er than the numbel' ofporcnt w iIN K" missed . Sco;ondIy. in real life, rcnC'Clionlfrom slMII SUrfKU I-re generally mucb ""C.ker ' hI-fical~l.ttd by the ..... , of gcornctrical KOUItics, 50 any suchre flection s miurd by the mode l 1fT in reI-lily of les ssipirlQ/tCCtlwt the model ibcl f_1d SIIUest . Actually. theefforts of an extended wo:u ll-tion mlly Iud to worw results

Recent upcriments ",i!h Ihe ODEOS PfOlra m hI _eshcrwn thaI only Soo to 1000 ra~s Ill: sufficient 10 obtai nnd il-b1e n:iuh s in a !)'pica l auditorium, end In optimumtransit ion order hu bcCfIfound to be t....o or Ihree. This me;JllSthai I-hybri d model like this can give much bcnc r result l thaneither of ute pure basic melhods. and with much shortercalc ulation time. However, these good news arc close lyrelatedlo lhe introdu etion ofdilfusi oni n the mndcl .

3. DlH' USION 01-' SOUI"D II" CO:\IPUTER1\I0DE LS

Thescaneri nl of soundfrorn,urfl.CC'1 cnbeqUl.flli( lrd by ascancrin g coeffICient. wflich ma~ be defined u foIl~: TheKl-ncri ng oocfflcic nl " of a s..nace is the n1rio bcIwem

VOl. 23 {199S1No. 3 · B3

reflected sound power in non-specular direetiol\ll IlIld the Iolalreflected sound power- The definit ion applies (or a ccrta inangle of incidence, and the reflected power is supposed 10 beeither specula rly reflected or scattered . One wukneu of thedefin ition is that it docs not say what the direc liolUlldinri bution of the 1iU1Iercd power is; even if (, . I thedirectio nal distribution could be vcry uneven.

According to the abavedefutitionthe seanc redpolloUP....clllbe expressedas:

P",.. -6P«/I _6(I_ a )P_ (4)

where P.." is the total reflect ed power, p... is the inciden tpower and a is the absorpt ion coeffi cient of the surface. Thescattering coeffic ienl may take values between 0 and LwberelJ.O meanspurelyspecularreficetion andlJ .l means thata llrefleclCdpower is scattered according to some kind of ' ideal'diffusivity. .

We now consider a small wall clement dS which is hit by aplane sound wave with the intensity I~ and the ang le ofincidence 8 relative 10 the wall normal. The incident power isthus l~d Scos !J . The reflected soun d can be regarded asem itted from a small source located on the wall clement andthe three-di mensiona l scatte r of reflected sound can bedescribcdby adireclivi tyDft,f" AtadistancerfromlbcwaUclement the intensity of refl ecte d sound is

1•.• • D; .{;;r .D•.• f0 C058~dS (5)

An omnidirecliona l source on the wall would bave thedirect ivity D... • 2, but instead ideal diffusc rd lections shouldfollow lambert 's eosi llC law: in any direction (!J,,) theinlensiry ofscancrcd sound is proportional to cos8, i.e.proportio nal 10 the projection of the wall area. The incidentpcwer on a surface exposed by a diffuse sound fie ld wouldalso obey Lambert'slaw. so this mus t be considered the idealangula r distribution

If the scattered sound power is assumed 10 be independentOf lheazimuth angle 4',the angula r distribut ion can be foundas a function of the elevation angle 8. For a given 81he soundpower is em itted th rough a ring with height rdOand rad iusr"inll, sothal

dP•• f .,,2Jrr 1sinOde - P,qd' Da.• sin8 dO (6)

which for the Lambert directivity D~ - 4cos8 leads 10

dPa-P"",2 eosO sinOd8-P"</lsin28d8 (7)

Hence, the angular dis tribu tion of idcal diffu sc rellec lions isl in28.

Diffuse re flection s can be simula ted in computer mooclsby $lalis tical mClhods [10). Using ranccm numbers thedirection of a diffuse reflectioniscalculated with a probabilityfunel ion I t cording to Lambert's eosme-law, while lhedircelioo of a specular reflec tion is calculated according 10

Snell" law. A s<:allering coe fficienl bctweenO and I is thenuscd as a weighting factor in averaging the coordinat es of thetwo directional vectors which correspond to diffu se orspecular reflectionrespectively

84 . Vol. 23 (1995) No. 3

Figure 4,One sound ray in 1 simple room wilh differenl V1I]UC'S

o( thc . urfacesc.llncriog coclficicnt

An example of ray tracing with different valucs of thescanering coeffic ient is shown in Fig. 4. The room is arcclll1gular box with a relativelylow ceiling. Allsutfaces arcassigned lhe same scattering coc fficienl. Without scauering,the nly tri>Cing displays a simple geometrical pauern due 10

specular reflections. A small scattering coe fficie nt of 0.02than gcs the late part of the reflec tio n patt ern , and a value ofO.20 is sllfficienttoobtainadiffusc looking rcsull.

By compariso n of computer simulations and meas uredreverberati on times in some cases where the abwrptionccefficiert is known, it has been found thal the scaneringcoe fficien t should norma lly be SCI 10 around 0 . 1 for larg e,planc surfaces and 10around 0.7 for highly irregu lar surfaces.Scaneriog eoe fflcients as low as 0.02 have been found instudie sofa reverberation chamberwithout diffusing clements.Tbe extreme values of 0 and I sbouldbe avoidedin computersimulations. In principle thc sca tteri ng coe ff icient varies withthe frcqueneyirscattering due to the fin ite siu of a surface i.mosl pronounc ed at low frequencies , where as scattering due10 irregu larities of the surface occurs al bigh frequencies.However, today" know ledge about whicb values of thescalteringc oefficienl are realistic is very limiled, and 00 far i.seem s . uff ie ient to eharact crize each surface by only onescan ering cce fflcie m, valid for all frequ encies.

4, ACCURACY Mi D CALCULATIO~ TIM ERcuntly an internati onal round rob in has bee n carried out[I I) with 16parneipants, most of them developers of softwarefor room acous tical simulat ions. In an 1800 m' auditoriume:ght aro ustical cri lcria as defincd in 112] wereca lculated forthe 11cHz octave band in the ten combina tions o f two sourcepositions and five receiv er positions. For compariso nmeasurements were made in the sam e positions by sevendifferent part icipants. Drawings, photos, maleria l descriptionsand absorp tio n coefficie nts were provided. It cam e out thatonlythrec programs can be assumed to give unquestion ablyreliable results, The resu lts of these program s differ from theaverage measurement results by the same order of magnitude

Acous tics AI,I$I,/Ilia

as the individual measurement results. So, the reproducibilityof the best computer simulations can be said to be as good asa measurement, which is quite satisfactory. However,some ofthe programs produced 5-6 times higher differences. It isinteresting to note, that the three best programs (one of whichis the ODEON program) use some kind of diffuse reflections,whereas the results from purely specular models were moreoutlying. It is also typical that the best programs do neitherrequire extremely long calculation times nor extremelydetailed room geometries.

5. ADVANTAGESOF COMPUTER MODELSCOMPARED TO SCALE MODELS

It is quite obvious that a computer model is much moreflexible thana scale model. It is easy to modify the geometryof a computer model, and the surface materials can bechanged just by changing the absorption coefficients. Thecomputer model is fast, typically a new set of results areavailable a few hours after some changes to the model havebeen proposed. But the advantages are not restricted to timeand costs. The most important advantage is probably that theresults can be visualised and analysed much better because acomputer model contains more information than a set ofmeasurements done in a scale model with small microphones.

5.1 The Reflectogram as a Tool

The reflectogram displays the arrival of early reflections to areceiver. When the early reflections are calculated fromdetected image sources, it follows that each single reflectioncan be separated independently of the density of reflections,and in addition to arrival time and energy it is possible to getinformation about the direction and which surfaces areinvolved in the reflection path. The latter can be very useful ifa particular reflection should be removed or modified.

5.2 Display of Reflection Paths

The reflection paths for all early reflections may be visualisedin 3D and analysed in detail. Duringthedesignofaroomitmaybe interesting to see which surfaces are active in creatingthe early reflections. Although it is difficult to extract specificresults from such a spatial analysis, it can help to understandhow a room responds to sound.

5.3 Grid Response Displays

With a computer model it is straight forward to calculate theresponse at a large number of receivers distributed in a gridthat covers the audience area. Such calculations are typicallydone over night, and it is extremely useful for the acousticdesigner to see a mapping of the spatial distribution ofacoustical parameters. Uneven sound distribution andacoustically weak spots can easily be localized andappropriate countermeasures taken.

5.4 Auralisation

In principle it is possible to use impulse responses measuredina scale model forauralisation. However,thequalitymaysuffer seriously due to non-ideal transducers. Thetransducersare one reason that the computer model is superior for

auralisation.Anotherreasonisthattheinformationabouteachreflection's direction of arrival allows a more sophisticatedmodelling of the listener's head-related transfer function.

Most of the recent research conceming auralisation hasconcentrated on the 'correct' approach,wherebyeachlinkinthe chain from source to receiver may be modelled as animpulse response. See Kleiner et al. [13] for an overview ofthe technique. However, the convolution technique involvedrequires either expensive hardware for real-time convolutionor Jongwaits for off-line convolution, and often the impulseresponse is too short to produce a realistic reverberation. Analternative technique for auralisation, which avoids theconvolution bottleneck, has recently been proposed [14]. Themethod is based on an interface between a digital audiomainframe and a room acoustical computer model. Thismeans that auralisation can follow immediately after the roomacoustical calculation in a receiving point, and there are nolimitations on length of the source signal. The earlyreflections and the late reverberant reflections are treated bytwo different techniques. With this technique 40-50 earlyreflections will usually be sufficient to create a realisticsounding room simulation, and long reverberation time is noproblem.

The early reflections are very important for obtaining arealisticauralisation. For presentation through headphonesthe following three methods are used in order to obtainlocalization outside the head:

• Interaural time difference. This is the dominant cue forlocalization of broad band sound in the horizontal plane.

• Interaural intensity difference. The signal to the ear in thedirection of the incident reflection is raised up to 6 dB.This is a simplified representation of the reflection effectof the head relative to free field.'

• Spectral cues. The spectral peaks and notches due to theouter ear arc roughly simulated by filters Although this isknown to be the main cue for elevation, the intention atthis stage has not been to create a localization fordifTerentelevation angles, but rather to avoid the front-backconfusion and to improve the out-of-the-headlocalization.

The auralisationtechnique ofTersthe possibility to use theears already during the design process. Several acousticalproblems in a room can easily be detected with the ears,whereas they may be difficult to express with a parameter thatcan be calculated.

6. CONCLUSIONComputer techniques for simulation of sound in rooms haveimproved significantly in recent years, and for the consultantthe computer model offers several advantages compared to thescale model. The scattering of sound from surfaces hasappeared to be very important in room acoustical simulationtechnique,andthishascreatedaneedforbetterinformationabout the scattering properties of materials and structures.Although the scattering can be handled by the model, theknowledge about which scatteringcoefTicients to use is very

Vol. 23 (1995) NO.3 - 85

sparse. So, it can be concluded that there is a need for a

method to measure the scattering coefficient of surfaces.

Until then there remains an inherent piece of guesswork in

room acoustical simulations. On the other hand, it is no

surprise that the user can influence the quality ofa simulation.

REFERENCESI. A. Krokstad, S. Stroem, and S. Soersdal, "Calculating the

Acoustical Room Response by the use of a Ray TracingTechnique"J.SoundVib.8,118-125(1968).

2. A. Kulowski, "Algorithmic Representation of the Ray TracingTechnique" Applied Acoustics 18, 449-469 (1985).

3. 1P. Vian, and D. van Maercke, "Calculation of the Room ImpulseResponse using a Ray-Tracing Method" Proc. ICA Symposiumon Acoustics and Theatre Planning for the Performing Arts,Vancouver, Canada (1986)pp. 74-78.

4. T. Lewers, "A Combined Beam Tracing and Radiant ExchangeComputer Model of Room Acoustics" Applied Acoustics 38,161-178(1993).

5. 1B. Allen, and D.A. Berkley, "Image method for efficientlysimulatingsmall-roomacoustics"J Acoust. Soc. Am. 65,943­950(1979).

6.1Borish,"Extensionoftheimagemodeltoarbitrarypolyhedra"J.Acoust.Soc.Am.75,1827-1836(1984)

7. M. vorlander, "Simulation of the transient and steady-statesound propagation in rooms using a new combined ray­

tracing/image-source algorithm" J Acoust. Soc. Am. 86, 172-178

(1989).

8. a.M. Naylor, "ODEON - Another Hybrid Room Acoustical

Modei"AppliedAcoustics38,13l-l43(l993).

9. a.M. Naylor, "Treatment of Early and Late Reflections in a

Hybrid Computer Model for Room Acoustics" 124th ASAMeeting, New Orleans (1992) Paper 3aAA2.

10.0. Stephenson, "Eine Schallteilchen-computer-simulation zur

Berechnung fur die Horsamkeit in Konzertsalen massgebenden

Parameter".Acustica59,1-20(1985).

II. M. Vorlander,"International Round Robin on Room Acoustical

Computer Simulations" Proc. 15th International Congress 011

Acoustics, Trondheim, Norway (l995)voI.Il pp. 689-692

12. ISOIDIS 3382 "Measurement of the reverberation time of rooms

with reference to other aeoustical parameters" (1995).

13. M. Kleiner, B.-I. Dalenback and P. Svensson, "Auralization - An

Overview,"J Audio Eng. Soc. 41,861-875(1993).

14. lH. Rindel, C. Lynge, G. Naylor and K. Rishoej, "The Use of a

Digital Audio Mainframe for Room Acoustical Auralization,"

96th Convention of the Audio Engineering Society, Amsterdam

(1994),AESPreprint3860

TONTiNE POLYESTERACOUSTIC INSULATION

• Tontine Sound Batts

• Tontine Black Liner

• Tontine Foiled & Faced Polyester Pads

Suitable for specialised acoustic insulation suchasrecording studios,cinemas, entertainment centres,auditoriums, air-conditioning duct,wallinfillandceilingoverlays.

Full technical dataavailable on request,

TONTINEINDUSTRIES

FIBRES DIVISION

THESAFE & GREEN

ALTERNATIVEIN INSULATION

HEAD OFFICE & VICTORIAN BRANCH:-

238Maroondah Highway Mooroolbark 3138 Tel: (03)97271100 Fax (03)92150043TASMANIA:- Tel: (003) 263888Fax (003) 265471 SOUTH AUSTRALIA:- Tel: (08)3463137 Fax: (08)3401499

NEW SOUTH WALES:-Tel: (02)7251533Fax: (02)6042410QUEENSLAND:- Tel (07) 38654066 Fax: (07)38654060WESTERN AUSTRALlA:- Tel: (09)3171444 Fax: (09)3172144

TonlinelndustriesAdivisionoIPacilICDunlopltd.ACN004085330

86 - Vol. 23 (1995) NO.3

Predicting the Acoustics of Concert Halls Using anArtificial Neural Network

FergusFricke and Chan Hoon HaanDepartment of Architectural and Design ScienceUniversity of SydneyNSW 2006 Australia

Abstract: An alternative approach to the design of concert halls, using artificial neural networks, has beeninvestigated.As part of the study,visitingmusiciansandconductors wereasked to complete a questionnaireontheir preferences for over 60 concert halls,most of whichwere locatedin Europeand North America. A similiarsurvey was carried out using membersof the Music Critics Associationin the USA. These results were used tocorrelate hall preferences with physicalfeaturesof the halls. It was found that the single most important featureaffecting the acoustics of halls was the diffusionof the interior surfaces. A preliminaryneural network analysisshowed a high correlation between the predicted and assessed acoustical ratings of halls when only sevengeometrical factors were used to describethe halls used in the study. The paper also reports on the comparisonofevaluationsof concert halls by musiciansand music criticsand the preferencesofbothgroupsfordifferenttypesof halls.

1. INTRODUCTIONThere appear to be several ways in which the complexity ofacoustic design of concert halls is handled. One way is to copyor modify an existing building, another is to measure acousticparameters in existing, model or virtual buildings and then toreproduce these parameters in the new concert hall. None ofthese is very satisfactory as there are many reasons, not theleast of which are cost and inaccurate modelling andmeasurement,whichmeanthatexactreplicasofhalls,orexactprototypes, cannot be built (or are not built). Often theacousticdesignofahallcomesdowntotheexperienceofthedesigner who over the years gains a feel for what works andwhat doesn't or who has an innate understanding of what todo.

Sabine's (1900) work on reverberation time was offundamental importance in the application of science toarchitectural design. Unfortunately the use of Sabine's workdoes not guarantee good acoustics and it would seem thatdespite the best efforts of Beranek (1962) and others toprovide an analytic approach to acoustical design, involvingfactors other than reverberation time, there is still noreasonable expectation that a new concert hall's acoustic willbe praised by musicians and audiences.

Concert hall acoustics is a multi-criteria and multi­parameter issue. The requirements for one criteria may becontrary to those for another. For example it is considered thata long narrow hall gives the best conditions for strong lateralreflections which have been shown to be important. The samelong narrow hall would not give good conditions for intimacywhich is also sought after. A longer than optimumreverberation time may be acceptable in a large hall butunacceptable in a small hall. There is little understanding of

Acoustics Australia

these and other interactions and the search for a singlemeasure of acoustics continues with the religious fervour oftrue believers,

While there is always the hope that some quantity, such asthe Interaural Crosscorrelation Coefficient (IACC), will turnout to be a single suitable acoustic measure, it seems unlikely.As described by Ando (1985) the IACC measurement requiresa dummy head to face the centre of the stage in an auditoriumas the measurement is dependent on direction. In someconcert halls the position of the performers can be changedand in all concert halls the members of the audience can movetheir heads without the perceived acoustic changing. Whilethis anomaly should not rule out the possibility of the successof IACC, or similar binaural measures, it is unfortunate if ameasure of performance cannot be directly related toperceived conditions. For this and other reasons, such as thelack of success in applying conventional parametrictechniques to auditorium design, it seems worth investigatingother approaches.

One such approach which formalizes the successfuldesigner's approach is the use of artificial neural networks toseek out the interrelationships in complex situations. The wayin which neural networks operate has been described recentlyby Baillie and Mathew (1994) and so this will not be coveredin this paper. Suffice to say that the use of artificial neuralnetworksobviatestheneedtospecify,calculateandmeasureacoustic quantities. The acoustics ofa space depends on thesize, shape and surface finishes of that space and if thesefactors can be adequately specified and if there are adequateexamples of existing concert halls where these factors areknown, and where subjective acoustic ratings have beenobtained, then artificial neural networks can be used to predicthow well a new hall will be perceived.

Vol. 23 (1995) No.3· 87

This paper should only be considered as a first attempt atapplying a neural network approach as there are a number ofissues which need refining.

2. SUBJECTIVE RATING OF HALLSFor this study a subjective rating of concert halls had to beobtained. It is inordinately difficult to obtain subjectivecomparisons of different auditoria. This is partly becausepeople have limited knowledge of halls, partly because peopletend to prefer the halls they know and partly due to a host ofother factors. One of these is that the acoustical conditions ina hall vary from seat to seat and now, with halls havingvariable acoustics, from performance to performance and evenwithin a performance.

Ideally a group of performers and listeners should be takenblindfolded to many halls around the world and they shouldplay and listen to the same music in each hall and in differentseats in each hall. Even this ideal scenario is unlikely toproduce much useful information because of the difficulty inremembering the different halls and performances andbecoming accustomed to the music. Unfortunately there is nomusical equivalent of the speech intelligibility test.

The alternative is to record music played in halls, using adummy head, and reproduce it in an anechoic laboratorywhere subjects can make preference judgements between pairsof"halls"without.tJlovingandwithout the use of semanticscales. This has been done by Schroeder (1974), Plenge(1975), Ando (1985) 'and others but there is always theconcern that the virtual acoustics may not be the same as theactual acoustics and that there may be important non­acoustical factors which influence judgements.

Somerville (1953) argued that the best group of subjectsfor surveys on the acoustical quality of halls are music criticsbecause they gave more concordant answers than performingmusicians, engineers, and the general public. But, in hisresearch,onlyten concert halls in the U'K, were considered.Parkin (1952) also insisted that the artists tend to evaluate thehalls only from their experience on the stage where theacoustic conditions could be quite different from those at theseats of the listeners. Surprisingly there does not appear tohave been an attempt to correlate the judgements of musiciansand critics about existing concert halls to test thesecontentions. Such a comparison is reported in this paper.

In practice, if the acoustic evaluation of concert halls is tobe extended beyond national borders, to maximize the rangeof designs studied and minimize prejudices, some of the bestpeople to make these evaluations are internationally acclaimedconductors and soloists as they have the knowledge of halls,the expertise to evaluate them, many opportunities to visithalls, due to regular concert engagements, and the need toconsider what the audience hears rather than just the stageacoustics. lt could be argued too that if musicians don't likethe stage acoustics the acoustics in the auditorium are unlikelyto be judged as excellent as the music played in the hall willbe adversely affected by the stage acoustics.

Past questionnaire surveys have been of two types: onefavouring preference comparisons, the other semantic

SB-Vol. 23 (1995) NO.3

differential ratings. Preference comparisons were undertakenby Hawkes and Douglas (1971) and Schroeder et al.(1974)whilst semantic scales were used by Wilkens (1975) andBarron (l988).

Parkin etal.(I952) described a subjective investigation often British concert halls by means ofaquestionnaire sent topeople who were music critics, music academics andcomposers. Of the 170 questionnaires sent out 75 werereturned. Only 42 of these responses could be used to beevaluate halls because the rest had experience of less thanthree of the named halls in the questionnaire. This study is thefirst known attempt to rate the general acoustic quality of hallsnumerically using subjects from the music profession. Theevaluation of the halls was made using a three point scale(good, fair and bad).

Beranek(1962)interviewed23musiciansand21criticstojudge the acoustic quality of the 54 halls (ie. 35 concert halls,7 opera halls and 12 multi-purpose halls) in his study. Theseacoustic quality judgements were used to construct numericalrating scales of acoustic attributes. The 54 halls wereclassified into five groups based on the musicians'impressions and evaluations. Beranek interviewed outstandingmusicians as a first source of reliable information in his studyof halls for music.

In the present study it was decided to ask musicians toevaluate the acoustics of halls using a self-administeredquestionnaire. The present survey was designed to reassess theacoustics of many halls used in Beranek's study and also toinclude as many different shapes of halls as possible in orderto investigate the effects of hall geometry on the acousticquality.

3. THE QUESTIONNAIREThe present work appears to be the first international study ofhalls,undertakensinceBeranek'sinI962,toquantifyacousticquality from systematic subjective responses. Thequestionnaire used in the study employed a three point scale(like Parkin used) and included concert halls only.

3.1 Questions

In the survey, using a self-administered questionnaire,respondents were asked to express their opinions on theacoustics of up to 75 concert halls. Respondents were asked tomake judgements about the acoustics of halls for classicalsymphonic music. The questionnaire included questionsabout preferences for music and concert halls. A list ofconcert halls was included and respondents were asked to ratethem acoustically, based on their experience, as eitherexcellent, good or mediocre. The terminologies used for threelevels of acoustic quality were suggested by Lawrence (1983).

A three point scale was employed for rating acousticalquality of the halls because it simplifies the subject's task andmakes the difference clear. As all the listed halls in the presentsurvey are well known and are regularly used for concerts theacoustics of these halls are not likely to be bad. Thus theordering scale was designed to start from "mediocre" and used"good" and "excellent" as the other two steps.

3.2 Selection of HallsMost of the halls listed in the questionnaire were located inEurope and North America. The halls were chosen becauseinformation about them was readily available in the literatureand because they are well known, so the sample is not arandom one. The list of halls includes halls with four differentshapes, ie. rectangular, fan, horseshoe and geometric,althougheategorizationintooneofthesewasnotalwayseasy.The list of halls was altered slightly during the three years inwhich the questionnaire was administered so that the numberof assessed halls could be maximized. A sample of the concerthalls which were listed in the questionnaire, and for whichthere were sufficient responses to make evaluations, is shownin TableI.

3.3 Respondents

The subjects for this survey were drawn from two groups:musicians who performed in Australia during the 1990,91 &92 concert seasons and members of the Music CriticsAssociation in the USA. The music critics' results were usedto compare the ratings of musicians with music eritics and, tosome extent, the stage acoustics with the auditorium acousticsof halls.

Most of the musician questionnaire respondents wereconductors and soloists from Australia, Europe, Japan andNorth America, who have performed as guest artists withmany different orchestras in many auditoria in manycountries. One of the added advantages of using this cohort ofmusicians is that the results should not be influenced by localcultural factors. A total of 110 questionnaires were sent tomusicians. Thirty five responses were obtained (ie. a29%response). The respondents came from 12 countries andcomprised 16 conductors, 13 soloists and 3 other musicians.All the musicians were professionals who performed regularlyin many auditoria. Among the 32 musicians, 21 performedmore than once a week and the rest performed at least once amonth.

A second evaluation of concert halls was undertaken usingmembers of the Music Critics Association of the USA.Despite the limitations ofa poor response rate (approximately10%), limited knowledge of halls outside the USA, possiblepreconceptions and other confounding influences, overallthere is a strong correlation between the opinions of themusicians and the critics. Opinions on individual halls diddiffer between the two groups but the most notable point wasthe spread of opinions on a number of the halls within eachgroup of respondents.

4. ACOUSTIC QUALITY INDEX OF HALLSRespondents commented on 60 of the halls listed in thequestionnaire. The largest number of halls any individualrespondent rated was 41. A total of805 ratings were obtainedfrom the musicians. The average number of ratings for eachhall was fifteen with a maximum of 30 for the Sydney OperaHouse Concert Hall. For the evaluation of the acoustic qualityofa hall at least 5 responses were required.

For estimating the goodness of the halls a value of I was

assignedtothoseassessedas'Excellent',0.5to'Good'andOto 'Mediocre'. An acoustic quality index (AQI) for each hallwas calculated by averaging the rated values. The "musician"AQIvalues of halls are distributed in the range 0.22 (Henry &Edsel Ford Auditorium, Detroit) to 0.98 (GrosserMusikvereinssaal, Vienna) while the "critic" AQIs rangedfrom 0.19 (Gasteig Philharmonie Hall, Munich) to 0.94(Symphony Hall, Boston). The "musician" AQI values foreach hall are listed in Table 1 with the details of the numberof responses on which the AQI was based.

The acoustic quality of halls, as rated by the music critics,is compared with the ratings of the same halls by musicians inFig I, for the halls for which there were sufficient responsesfrom both groups. The agreement is surprisingly goodconsidering that the acoustics of the stage and auditorium inagiven concert hall could be very different. There appears to bebetter agreement between the ratings of critics and musiciansin conventional shaped halls than in fan or geometricallyshaped halls such as the Berlin Philharmonie.

Figure I. Scattergramof hall AQIs as determinedby criticsand musicians. .

5. ACOUSTIC QUALITY DEPENDENCE ONHALL GEOMETRY

To undertake a neural network analysis it is not necessary toinvestigatethccorrelationbetween different parameters andthe acoustical quality of the auditoria but such an analysis isof general interest and so some of the relationships arereported on below. In the present study 28 of the 32 musicianrespondents said they had a particular preference for hallshape for symphonic music. Regarding the hall type it wasfound that 21 of the 28 musicians (75%) who answered thisquestion preferred rectangular concert halls. The second mostcommon preference was for horseshoe type halls. This is inaccordance with the finding of Gade (1981) who indicatedthat musicians preferred shoebox type halls as an ideal roomshape. Nine of the twenty halls (45%) which have AQI's of0.60 or better are rectangular in shape whilst only 19 of the 53halls surveyed were rectangular halls (36%). As might beexpected this is a similar trend to that for the musicianspreferring rectangular halls.

While the overall acoustic impression of symphonic musicplayed in halls was used to estimate the acoustic quality indexof each hall, the appropriate shape of halls for other types of

Vol. 23 (1995) No.3 - 89

Ta ble I. Aco \l5l icquality index o f conc:ert lLaJis

con«rt li ail hail E d AQ' AQ[T",. (musician ",opon Sel) (musiciam) (cr iTics)

Grouer Mu. ihen:imsaal, Vien na REC 26 25 , 0 '" .OlSymphony Hall, Booton ,",C re "

, 0 " "C<!ncertsewuw, Am. teroam Rf.C 26 23 ) 0 ." .saClmegie IIln . New York 115U 28 19 , 0 .... OlSewra nce HIli , CllM!land !l SU [[ 8 l ,

" 81Gev.'andhn s, ~il'li l OED 10 6 · 0 80X "Concert I IaU De Doelen, k olterdam GEO 11 s 8 0 rtBerliner I'hilllllmonie lI all, Berlin OED 23 " 7 l .76Dem gale Cmler. Northampton R£C 10 , · , ruxHer1<uIe...... I.M unich Rf.C 19 , · l 68 soOn:IleOlraHall,Chical o IISU ae 7 II , ss saGroMCr Tonhal leoaal, Zuric h Rf,C IS 6 [[ , .64 "TbeM~h.ani"Hall,Won:nler Re C 8 l 6 0 ea .S7Conc m Hall, Hau lem REC , , a 2 .61XRll)'aI Concen HaU, NollinSbam OED , ) s , .61XCon cert Il all De Oooterpoort fAN s 2 7 0 6lXPhilade lphil Academy of Mllsic IISU "

, , , .eiCIlfINiel~n lllll ,Odense REC 10 2 8 0 .OOXNeue s FC'SI"l'ielhau . , Sa!zb lll\l fA N " a [) 0 .ssSladt-Cl$ino.Baoel R£C II ) 8 I saOslo Concert Il all, 0010 f AS 8 2 s ,

"XConc en ll all.Sydncy Ope ra House OEO 30 6 21 ) .~ ~X

Coocen llall .SlOCkholm R£C II ) 7 2 S"Palais de laM usique, Slra WuQl OEO [) 2 10 ,

.~4X

lJlh er Hall, Edinboo'ih . SU " 2 ", .sa

LiftIe1baJle Gro<oet Saal , SIUlTgaTl OEO " ) · , .scSI_~i llal l .Glasiow R£C [) a , 2 .SO:Berwald Hall. SlOCkbolm OED 8 , 6 , .SOXLyric Tbeat,.."B altimo,.., REC 7 0 7 0 .scWar Memorial Opc rl UOllW, S.F HSU . 0 · 0 .soPhilharmoni c 11111. Liverpool FAN " l [) , .,.NalionaI Concen ll l n, Dublin, E in: REC [) 2 8 ,

' 6XMeloollme Concetlllall .M e lwllI"lle OEO 25 S [) 7 46XTmli Koru::cn, "I, Cop enhl gen 'AN II 0 [[ , 46 .scConce n HalJ,Kennedy Cenl er REC IS 3 10 , 44X .,Co I'ton Hall. ll,; " ol REC "

, [[ , .,EastmlnTbeat,.." Roc:hnl er f AN II 0 10 2 .,Conce n llal l,M usic Center, Ulrtc ht OED [[ 0 , 2 ARadioh <aoetSrudio l , Copc nhagcn 'A.' , , , ) .) 9·RoyaI FC'StiwJ lla ll,London ReC 29 6 s " 36Fm: Trade ll all, Man<he stet Re C IS , [[ 6 36Palaisdcs Beaux-Art s,a"'s.oel . SU IS , [l 6 .36 .,Ga>teigPhilharmon ie, Mu n;ch FAN " 2 6 6 ,) 6X 19B«tl>ovmhalle, Bonn OED 17 2 8 7 .as "RoyThomson li all, Toro nlo OED 10 2 3 s 3 19Maison de Rad ;o Ftance. Paris FAN " 0 [l s ,.Gl"<lIlotTSende-a al,Heri in ' AN [[ , , 6 .27Avery Fi&her HolI, New York " C 16 l 10 [l .zt-x 31Boc:ncher C<!nccn ll all ,l> enver OEO 10 0 , , 2SX "B. rbican Concert 11. 11, Lo noon OEO 16 , 10 " .n -x "Hcnry Ford Au ditol'iurn. D!:tro it FAN , 0 · , 22: .31

• All or pan of the se s ubjec live evaluations ma y have been ma de be fore recent changes in the ha lls .

: Ha ll no lo nger ex isl sX Ha ll le ss th an J O yea n o ld .

Where, Ihe abbrc:vialions used in th is Table are as foll ow s ;REC : Rectangu lar hall fA N : Fan shaped hall " SU : Ho rses hoe (U shaped) ha ll OEQ .Geometricalty shaped hallTotal : Total number o f re sp on denIS

ErExc ellent G:G ood M:Mcdiocre AQ1: Acoustic qualuyindex

90 , Vol 23 (19 9 5} No 3 Acousncs Austraba

musical performances was also investigated. Thequestionnaire respond ents were asked to indicate the belilshape for three forms of music; symphonic , chamber &I;50010

recital aad cpe ra . Table 2 sho\o.'S!he nurnberof rcspondentswho preferred particu lar hall shape s for panicular musicform s. The survey showed !hal more than half the musiciansalso preferred rectangular halls for chamber music and solorecitals . As expected, horses hoe type halls were preferr ed foroperatic performan ces. The geometric and arena halls areobviousl y not popular and thi s preference shou ld beconsidered asbeinsrnore significant!hantheoftenexprnsedpreference ofmusicians for wood lined interiors.

Table 2 . Surve y results 0 0 the preference for hall type fordifferent types of mus ical performanc e

fomt,.Dr Musie '....... a.m~ . -~HalIT )'pCI SolD Rtc ita l .-."'-~ " rc , ,r...Shapcd . , . .H.....hocShaped . , . ,o-nctnc ol Arcna , ,

"Sul>TDlal n 17__ ~-----.!....6_

There is a clear preferen ce, shown in Table 2, forrectan gular and horseshoe shaped halls compared with fanand geometricall y shaped halls, An analysis of preferences forhall shaPQ in Table l also shO'W1 thil trend bllt not w clearly.Grouping therectanilllarandhorseshoellallst~ther.ndthc

fan and gecmetrtc halls with AQIs " O.S and >0.5 andapplying a xa lest 10 the musicianresponses shows that thedifference is significa nt at the 1"1. level (DF~I , X2.6.&7&,O.OOI<p"O.OI).

The most signif ICant factor. by far, in produoeinS goodICOUlitics appean 10 be the degree of diffusion by thew.lIsand ceiling, This relation ship is a paper topic in itself but anexampleoft herelalionshipbelwee n the acouslicqualilyi ndCO'land a subject ively determined area weighted sur facedilfusivity indcx (SDI a.w.] is given in Fig 2 for rectangularhalls. Further informa tion is given in the following section... .. ........

. -"'" "'- - r=.t-I-- -I--

Figure 2. Scaltergram of Aoou,tic Quality Index (AQI) againstarea weighted Sound Difl'u, ion lndex (SDl a,w,) fO' re<:l.ingu]arhalls.

Acous tiCS AUSlfa lia

This relationship may have a non-acoustical aspect as wellas an acouslical aspec t. The design elTort required for a hallwith surface ornamentation may be an indication of theanent ion paid 10 the overall design as well as be visually morestimulat ing than plaine-rrreetrnents .

6. OTHER FACTORS INFLUENCINGPERCEIVED ACOUSTIC Q UALITY

~ost conce" hall s (94% of aU hall s used in the presentuiork) havca reverberanen time of more than 1.5 sec whenthey are occupied. The mean value of reverbe ruion tim e o fconcert halls used in this work is 1.77 sec with the minim umreverber ation time of 1.3 sec . II has been acknowledged( Beran ek, 1962) that suffic ienl reverberat ion lime is acruc ial requirement for good acouslics. If it is assumed thaIgoodhalls have adequat e di ffusion a long reve-rbcrat ion timewould not be an essent i. 1 COndition for a diffuse sound

field , When the ecousnc qua lity index was plotted as afuncti on o f reverb era tio n t ime o f ha lls, a ver y lowcorr elancn coefficienl was obtained (ref er to Fig ,3) with alarge amo unt of scatter. This in dicat es tha t a longreverbe ration time is nOl, on its O'oO'n, a II tis factory ind icalorof acoustic quality. Thi s point has been mad epreviously eg.Barron (198&) and Beran ek (1962). Also il is shown inParkin s ' study ( 1952) where the dtstnbution ofreverberation time and volume of halls are very widelyscaner ed, regard less ofl he qua lity of ha lls

:r--t----- ~ ~j:-i- :;j=.....--' f-~+- - -~ --:-.-.- -+-:1=4 -· ._I-=-t=±• ;-j-.. .. .. .. .. .. I I ,' H l>

Figure 3. The oeau~rgram of acoustic quality index alll,n. treverberation lime of hall.

Interestingly, of lhe halls listed in Table I, the five toprated hal1sw~reall over 30 years old ( atthetime of the study )

andthere"'e re only lu..:thal1s lessthan30 )'earsold in tl!e top10 halls. Of the halls listed, for which the re we re mor e than 5responses, 23 were less than 30 years old and 30 greaterthan30yearsold , l l should be noted that a number of the olderhalls have been renovated and iti t is not clear whelher theseshould be classified as new or old halls and ...hether therespo ndenu ...'ere rating lhe hall s befo re or afte r therenovations. However there iii a bette r correlatio n of acous ticquality with the age of the hall than there is with thereverberatio n time (see Fig 41.

Vol 23 (1995) No. 3· 91

.....••• e.

Using a Chi-squared test there is a p<.OOI that the hallratings are from the same populations when a breakdown ofhalls is used such that the halls in which the five most wellknown orchestras usually play are separated into one groupand the five other best known halls are used as the secondgroup. (Each hall had at least 10 individual ratings and thetotal number of ratings for each group was 133 and 130.)

Table.J Comparison of hall ratings with resident orchestras

Hall Rating AHalls

Figure4(a). Acousticquality of all halls as a functionof age(years).

BostonChicagoSeverance

MeyerhoffAveryFisherSanFrancisco

Figure4(b).Acoustic.qualityofrectangularhallsasafunctionof the age of halls (years).

It was considered possible that the judged quality of anauditorium might be related to the distance the respondentlived from the hall. There are several reasons for this includinga "cultural cringe" factor (halls further away are more highlyregarded) and the halls that are most familiar (near halls)being judged to give the best sound. Two analyses wereundertaken using information from the music critic survey: acorrelation between how good a hall is judged and the averagedistance away that the hall is (for all the respondents living inNorth America) and a second test using only the east coastcritics and halls. For all the respondents there was a slightcorrelation (r2=0.2) with the more distant halls beingconsidered lower quality. The result was significant at the10% level only and the relationship is considered to be anartifice of the distribution of halls and respondents (most hallsand respondents lived on the east coast and most of the betterhalls used for the study were in the east of the USA).

Of the respondents living in the east and commenting onthe east coast halls distance is not important when a Chi­squared test is carried out on two groupings: s250 milesdistant and >250 miles distant (DF=2, X2=2.468,

0.20<psO.30). If the "good" and "mediocre" categories arecombined the effect of distance is significant only at the 20%level: DF=I, X2=2.29, 0.IO<psO.20. It might be useful tocorrelate judgements with the place where the respondentgrew up but one can hardly design using this information andso the only possible value of it would be to indicate howimportant external factors are in the evaluation of halls.

92- Vol. 23 (1995) NO.3

Carnegie KennedyCentrePhiladelphia Rochester

This is not very convincing evidence that it is the orchestrathat determines what respondents think of the acoustics of anauditorium because it could well be that the better orchestrasevolve around the better halls and besides itis not known whatorchestras were playing in the halls when the respondentsmade their judgements (the New York Symphony Orchestraplays in the Avery Fisher and the Philadelphia Orchestra playsin Carnegie Hall, for instance, and all orchestras go on tour).

7. NEURAL NETWORK ANALYSISFor the neural network analysis only the musician responseswere used as the music critics did not comment on sufficienthalls for which other data was available.

A neural network analysis was undertaken to find the bestcombination of parameters for the prediction of goodacoustics of halls. Neural network analyses are mathematicalmodels oftheorised mind and brain activity which learnknowledge on interconnected variables by adaptivesimulation. The neural network is applicable to situationswhere only a few decisions are required from a massiveamount of data and situations where a complex nonlinearmapping must be learned (Simpson 1990). In the neuralnetwork analysis only geometrical data on the halls were usedfor the prediction of the acoustic quality of halls.

Geometrical data on 53 concert halls was obtainedtogether with subjective evaluations. The halls used in thisstudy are those for which published data is readily available inpublications and for which scaled drawings are available. Theplan and section in the 1/400 or l/500 scale was used tomeasure the geometric properties of halls. The sample,therefore, is unlikely to be random. The geometricalparameters used are shown in Table 4 with the abbreviation foreach.

Hall depth (HD) is defined as the distance between theproscenium wall and the rear wall. HW is the horizontaldistance between the side walls in rectangular halls. In thecase of non-rectangular halls, the hall width is the average

Table . Audilorium para meters used in the investigation

N. <mlmeuieaI1'ararTM.1en Abbreviation Unitor AlIditonum

I ..... ""- V mJNumber of Alldiencc " N -3 Total Floor Area S, mJ· AwIimol:Su.tin A". 50 mJ, -... ... V," mJ"'"·- -- V" ", ...... '"" ,.,....

•1Wl_

l ID .· A~. HalIWKlth NW m10 A~ HallHe; , 1111 m

" III WICldtRatio J>'W12 . "" .... J>Hu _."" .... ..'"" An Ic of SideWalb ASW

" Maximum Rakc An eo fSolln XRA16 M_ leo rHatI MRA '"" Surfar;:eDi t\'usi.vi .flWl SOl

widtbofdle plan which is c:oD'IU1ed 10 f'elCWlgularone that~ts lhc __ oflbc:ori&in&lba1I""1leJ'eIhc HWis

calcuWed based on fiMd HD . The hall height. HH, is Ibc:meandiSWll;e broocen tbc noorand Ihc crilin l ' The anile oftbe side ...al l.. ASW, is a simple measure of tbc shipe oftbeballs.ASW isthein<:ludedancleofthesidc ...a1l1 wbichis Ofor rettangv.1ar hall s. T_ me anlles of the IUD nl '<lUe

used; the mn imwn rake lillie of the Kalin&. XRA, and themean me 1Jl11e.MRA. Thesurf.,e d.ift\l$tvity of a hall is ameu lIR of how iffC'iUlar Ihc MIl'facn arc. Formis sbldy theevalu.ation of di lfusi\i ryof aurfaees .....s undertaken by visualinspec;tioo. A simple ea~coriwion WlS used &I it is ditrlC:UltIolU bjectively di ffercnliatrlUrfaeetUlinlmorrthana thrrrpoinI Kllc . Surfaees'Im'Cplaecd in oncofthrec elllq:oriesdrprndinlmainly oalhe iffC'iUlan ty or thr surfaees and lo alesser extent on the al»orplion of those surf.:es. The threecategories IIXd were high, medIum or low di ffusiviry. Thecri~ria for lhe classifica tion o f diffusivenr ss of lW'faces andweighlinS pmcrdurn art presemedin a previous paper (Haan1993). For numcti Citleva lUollion of lhrrffm ofdi ffilsiviry ofthe: surfaces I valurof I wu u signcd to the ' hii h" O.S 10' medium ' Ind 0 10 'l ow' diffusing surfaces . A surfK ediffusivity indc. (5DI...) for each hall was calculated by

avcTlIging thr diffusivity o fth r ceiling and walls to obtain anSDt1y in the: ranie 0 to I. It should be mentioned that theCltegorisation uscdinthe pre senl worlt is a f irsta llempt at asimple method ofdefinina di ffuli yity of surfae es and thaibeller war- of defin ins and eates orising of surfaces l hould beanempted. Likewise, better WI YI of dcfin ina: the aw rnctry ofhalls also need to bc invcl tia ated

Usina: Ihe abov e , eui ly determined, param eter s acorrel ation malrix was formed The parameters with thehigheslcorrelations ....ithAQI_re llX d in theaubsc:quC11.tneura l nctvoorlt analysis. The corrclalion matrix ,. 1hown inTabir S.

Acouslic a Austral..

Table S Correlat ion matrix of acometri eal para.metCTIandAQI.

___ ","",,", _ I_ _ _~ l

· 116 III IIWId<po11 . __ .J l) .-')<1 •.'11 I

H.oI..... ....... _ •.Q JI I .~" . , t J

.0.l1li<01'_ _ •.~21 J U -01'1 .Jt)ll li t I

_....... • III J IO J IJ •.~n 196 I_ --,. _ .10 .... ..100 _ .J_ . j tt I

There are lWOlla i:cs in the PfOCedur e of ncura l nctworlanalys ilie. uai ning andtcstinl. The lrI ininl ofanetwot1I:isthe makinsof a network model which Irama tile pattern ofinput dmo and SlOI'eI the w,.eilbrs which eonuin knowledgeaboul the condatioD~ die ndVo.:)rk COIlfil'Jl'ltioo andthe eIIanoeteristie$ of inpul dati- FiB_ S ilhlstnl1n the n-­diagra.rtl of neural oe'tworlc proerdutcs uradeTtaken i. the~nl ltudy.1"hegeomo:trie data dneribcdrarlier in this

!ieCUOII WC1't atloptcd as input variablcs fOl'anal)'ll s.

FlltUfeS. Flow dil ltram for l imulatlni proc:rdu~s of a neural

- "The program used in the prescnl study was Dime (ycrsion

1.2) which was Ik lign ed for espc-cilll y est imation andapprox imation purpo se. The nelll al network analyscs werecarried out using a micro Sun workstation.

It is important 10 haveeven distribution of sampled datafor the beth training and tnting sets of hall s. The data on inputand output \'lliablcs lltould be evenly distributed in order Illalthe informa tion C<:Ivtn the full range of JlOlSlblr vafces. Twobasiccri teria were used 10selectbaUI for both the training and~sting sets. Thepc:Ke ntai:e of each ball type of hal l in eachset shou ld be similar (approx imately 20%) and the AQI valursof balls for testing should cover the AQI rana:c uscd fornetwork mining _Table 6 lltOW5the req uired number ofha lls

'Yd. 23 11995J No, 3·9J

for testing. Ten of the 53 concert halls were chosen as halls fortesting networks. And the rest of the halls (ie. 43 halls) wereused for training the networks.

Table 6. The nurnberofhalls for testing networks.

-Number of Number ofHall Type Percentage of

Halls in Sample Halls for Testing Halls used for

Testing(%)

Rectangular 19 4 21.0

Fan 11 2 18.2

Horseshoe 7 I 14.3

Geometric 16 3 18.8

Sub-total 53 10 18.9

The ten concert halls which were selected for testingnetworks are listed in Table 7. The geometric halls includedone circular hall. The average acoustic quality indices of theboth sets of halls are shown in Table 8 with the range of thevalues.

Table 7. The list of concert halls used for testing the networkmodel.

Type AQI

1 Concertgebouw,Amsterdam Rectangular 0.942

; ~:~t~~:~:::,H:~~~~~ense Concert House :::::::; ~::~~2 RoyalFestivalHall,Lou"don Rectangular 0.362

5 TivoliConcertHall,Copenhagen Fan shaped 0.458

6 GrosserSendesaal,SenderFreiesBerlin Fan shaped 0.273

7 PhiladelphiaAcademyofMusic,Phil. Horseshoe shaped 0.607

8 Concert Hall De Doelen, Rotterdam Geometrical 0.765

9 BerwaldHall,Stoekholm 0.500

10 Roy Thomson Hall, Toronto 0.350

Table 8. The average AQI of both sets of halls used fortraining and testing networks.

8. RESULTSThe seven major geometrical attributes (highest

correlations with AQI) were used as input variables for theneural network analysis. Thus a network function was setupas follows;

AQI = f(VIN, SaIN, DfW, WIH, ASW, MRA, SDI)

For the calculation of acoustic quality,basedon thegeometry of the halls, the data on the geometryof43 hallswere used to train the networks. For the learning procedure theconvergence criteria was set to 0.000001 (error margin) andthe number of iterations started from 1,000,000 times. If thenetwork converged (ie. the network is fully trained by the

94 - Vol. 23 (1995) NO.3

input data) the calculated acoustic quality of the trained hallsshould be the same as the real acoustic quality index of thehalls. Fig. 6 shows the training regression line which has an r­squared value of I. This indicates that the network model usedwas fully trained that the prediction of acoustic quality of thenew halls would be possible to undertake.

Figure 6. The scattergram of acoustic quality index againstcalculatedacoustic quality of 43 halls which were used fortrainingof the neuralnetwork.

Further analysis showed that the highest correlationcoefficient was obtained when 5 geometric parameters (DfW,W/H, ASW. MRA, SDI) were used. Except for MRA, all theseparameters have a high linear correlation with the acousticquality of halls. Fig. 7 shows an r2 value of almost 0.7(r=O.835)when these parameters were used as input variablesfor the neural network analysis.

7',R-•• ,,,.,, •• 7

:;...-

-----.....-::.3~

---Figure 7, The scattergram of acoustic quality index againstcalculated acoustic quality of 10 concert halls which werepredictedby neuralnetworkanalysis,

8. DISCUSSION AND CONCLUSIONSThe present study indicates that musicians and music criticshave very similar opinions of halls, Previous concerns that theperceptions of players and audience members could be verydifferent do not appear to be justified, with the possibleexception of "geometrically" shaped auditoria. What is ofmore concern is that there are pronounced differences inopinion on the quality of the acoustics ofagiven hall. In somecases there were approximately equal numbers of musicians(and music critics) rating a hall as "excellent", "good" and"mediocre", Examples of such cases are Berlin Philharmonie

Hall, Berlin, Roy Thompson Hall, Toronto, NHK Hall, Toyko,the Academy of Music, Philadelphia and Joseph MeyerhoffSymphonie Hall, Baltimore. The shape of the hall issignificant. There is a marked preference for rectangular andhorseshoe shaped halls over fan and geometrically shapedhalls. More important appears to be the decoration and surfacefinishes in the halls which, besides influencing the diffusionof sound, also may be an influence on responses in other ways.

An individual's rating of an auditoria appears to depend onpersonal experiences and on factors other than just the hall'sacoustic characteristics, as indicated by the dependency on theresident orchestra and the distance the respondent is from thehall on the acoustical rating and expressions of preference forrectangular halls. The reverberation time ofa hall does notappear to be important though it must be stressed that therange of reverberation times was small. The age of anauditorium is of minor importance with the older halls beingconsidered better.

Whatever acoustical analysis is carried out for the designofa concert hall ultimately there is a need to establish arelationship between the geometry and the acoustic quality ofhalls. Using an artificial neural network this has been done.The reason for undertaking the analysis in this way is becausethis analysis is of greater use for designers, at least in theinitial stage of the design, as it directly links physical formwith acoustic performance. This is, however, at the expense ofunderstanding what is going on and designing within thelimits of parameters used in existing auditoria. The analysescarried out indicate that there is a good basis for using hallgeometry as a measure of acoustic performance. This paperalso indicates the importance of the several geometricalfactors on the acoustics of halls. It appears that the presentpredictions are better than any based on acoustical measuresof concert hall acoustics.

It should be also mentioned that most of the halls used inthis paper are well known halls which are regularly used forconcerts. This means that most of the halls are acousticallygood. Although the results clearly show a relationshipbetween acoustic quality of halls and the geometricalproperties of halls it should be reemphasized that the hallschosen for this study can not be considered a random sample.The halls are all 'good' halls and so the geometry of thesehalls can only be considered to influence how good the goodhalls are. The present paper, nevertheless, shows theimportance of shape and other geometrical properties inconcert hall design.

There is a need for further work. The most obvious is theneed to put objective measures of hall shape and surfacefinishes into the analysis. This work will be undertakentogether with the development ofa "music intelligibility test"for auditoria which, if successful, would obviate the need forsurveys such as that described early in this paper. Finally,although both musician and music critic opinions were soughtfor the present analysis, only the musician results were used inthe neural network analysis. It would be interesting to extendtheanalysis for strictly auditorium rather than "stage end"

Acoustics Australia

acoustic design but this is also possibly pointless, Aft" the lmusician survey had been carried out Leo Beranek wascritical of it because it was going to be stage-end biased. Athis instigation the survey of music critics was carried out.When shown the good correlation between the two surveysBeranek commented to the effect that it was to be expected asmusic critics formed their opinions based on what they heardfrom musicians!

ACKNOWLEDGMENTSThe authors are indebted to the Australian BroadcastingCorporation for administering the questionnaire survey tovisiting musicians who performed in ABC programs. Sincerethanks to Dr. David Gunaratnam at the University of Sydneyfor his kind guidance and valuable comments on the results ofthe neural network analysis. The authors are grateful to Dr.Marwan Jabri, of the Department of Electrical Engineering ofthe University of Sydney, for making the neural networkprogram, DIME,available for this study.

REFERENCESAndo,Y.(1985)Concert Hall Acoustics,Springer-Verlag,Berlin

Baillie, D. and Mathew,J. (1994) "Diagnosing rolling elementbearing faults with artificial neural networks" Acoust, Aust, 22,79-84.

3. Barron, M. (1988) "Subjective study of British symphonyconcert halls,"Acustica66, 1-14.

4. Beranek,L.L. (1962) Music, Acoustics and Architecture, JohnWiley,NewYork.

5. Gade, A.C. (1981) "Musicians' Ideas about Room AcousticalQualities", Report No. 31, The Acoustics Lab., TechnicalUniversityofDenmark,pp.55. '.

6. Hawkes, RJ. and Douglas, H., (1971) "Subjective acousticexperiencein concertauditoria,"Acustica 24 (5), 235-250.

7. Lawrence,A. (1983) "Sightline and soundlines-The design ofan audienceseatingarea,"App lied Acoustics 16,427-440

8. Parkin, P.H.,Scholes, W.E. and Derbyshire, A.G. (1952), "Thereverberationtimesoften Britishconcert halls,"Acustica 2,p.97.

9. Plenge, G., Lehmann, P., Wettschureck, R. and Wilkens, H(1975)"New methods in architectural investigationsto evaluatethe acoustic qualities of concert halls," J.Acoust.Soc.Am. 57,1292-1299.

10. Sabine,W.C.,(1900) "Reverberation", first published in TheAmerican Architect and Engineering Record and later inCollected Papers on Acoustics. Harvard UniversityPress, 1922

II. Schroeder, M.R., D.Gottlob, and Siebrasse, K.F. (1974)"Comparative study of European concert halls,"lAcoust.Soc.Am. 56, 1195-1201.

12. Simpson,P.K.(1990)Artificial Neural Systems, PergamonPress.

13. Somerville,T.(1953),"Anempiricalacousticcriterion",Acustica3,365.

14. Wilkens, H., (1975) "Mehrdimensionale BeschreibungSubjektiver Beurteilungen der Akustik von Konzertsalen."Dissertation,TUBerlin.

Vol. 23 (1995) NO.3 - 95

AcolllstDc Analysis And Test Data Processing

Products

Compumod olTers I comprehensi~e line of products for acousticand ~i""'iontestinlllUldan;olYIis. providing an integrat ed approachton oise, SUUC1Ural vibralionand lloCOllSlic srudiesProducb ind uok:

• SYSSOI SE Comprehensive acoustic simulat ion

• RA¥N O iSE SolDld ray 1J1>Cing

• MSC!NASTRAN Coupled nuid·SIl\lCtUn:. no ise and vibt'lltion

• ABAQUS AcoUSl.ic (>nite elemen lS

• l MS CAD.X Integrsted noi'lCand vibration tesl lahorstor)'

Service.

Compumooo ffers n lensive consulling serviccs fof af,lOuS/icandvibra!ioRstooies . Coupled with many ycars Finite ElemmlAnalyli s npcriencc "' . p1ovi<kI compreheRsh e approach 10

dcsi&n ln alysis w leslin&

More Information

If)'O\l \Oltlu l o;l likemore infonnaliorl, pl~ronlaCleilhaour

Sydney or Mel~meofficc

PIEZOFILMSE NSORS

[rendoo rel'r• •enls AM P Sensor Inc. in Aostrah a .. I .... lueldded resellcr oflhe ir !hin film piero eleclrie sm SOfI

n.e.coen,or. have very wide dynomie rangu and .f'uqUCI\C)' l'CSpoR llC from milli Hz 10 leR5ofme&Hl .

ArP licltian , ind udc• Vibration IRd Hl nn onic Ana!y,i s

SlIockllldSeisrnic quan lificl tionAcov.OIicemiuion and radiationNoise rnoni.oring lRde onlro lUnique smd·rc«i~ 'l(nsor pai rs

AcouSlicuiggn'lModal AnalysisS. euril)' mdSurvc:Hlancc

Sl&ndard lRdeUSlOm 'l(nsorconfigunlliofu, ~ lva.illblc .Piezo

e leclrie lRdpiezo..,sisli~film'Clln offer llniq"' 101uliOl'l' IO

difficultproblelt\$

Thinfilmlechno logyofTcrs ....ry low cosl . nd lOluliool.oproblem. previou.ly \:OnsideredlOOexpen .iVl:I" ... I~ wilh

eonvenlional lechoology.

IRE NDOS PH LTD.

37 Allison AvenueGlen Iris 3146 Vielor ia

phondfax03-98115- l6116rnob ile04I·934-4SJO

96 · Vol. 23 (1995) No. 3

>:; ~ :~ ..

COMPUMOD

,,..,Le~9.3(WPIIIS/1wtS)<ln.Y 2000

PtI_ . (02)2812~n

Fa (02)2832585-­Le" J, 468 S1 /(~_._m. JQ()I

PtIcntJ: (03)l182OJIMf n (ll3) 9820 J23lJ

NOISECONi~GfL

~~CIl,@$UJJ~~~

you can rely on.Fora l1you' noi",.ndo. u,.

.....-d'·froms""'lfl ik offun'l'l,, ' .ry l• .,.. dcmounlabt.."n.o:lurn , }'ou <an rd}' oore""e [ogi_nng

I\l r ' .K'<', ,,,. h.l,·. bft n d..;igniIJg. m.onufaeturi n~ .nd in.

" oI1ingnoi ... ronltt>l.........."..;i IlCl'IWtllo'i H ilnlll'lp ynu

rontrol """"'''' )'OOrpl4nl lmminlili.ol ""' .. ""'.............. ' 10oonh.:n.Ilion o/ f""riornu ..... ""oompie'tion

CaUNOW k>rd<1...I..

Some Notes On Sabine Rooms

David Alan BiesDepartment of Mechanical EngineeringUniversity of Adelaide, Adelaide 5005

Abstract: First the classical derivationof the Sabineequation describing the decayofadiffuse soundfieldinareverberantenclosedspace is reviewed.Nexta modaldescriptionof soundfield decayis proposedand three alter­native methods of solution are considered:(a) With appropriatesimplificationsthe Norris-Eyering equation isderived. From the latter equation the Sabineequationisderivedasafirst approxirnation.(b) Withaltemativeassumptionsthe Millington-Setteequationis derivedand the open windowdilemma,often cited, is resolved. (c)With further argument and one assumption the modal analysis leads to the Sabine equation but not as a firstapproximation.Experimental verification is demonstratedby making reference to data provided by a CSIROround robin which was conductedandreportedin 1980.It is shownthat all of the dataobtained in the latterinves­tigation in the seven rooms ranging in size from 106cubic meters to 607 cubic meters whichhad sufficient aux­iliarydiffusion and for all patch sizes tested may be redueedto one Iine in terms of the calculated statisticalabsorptioncoefficient for an infinite patch.A simple empiricalexpressionbased upon assumededge diffractioneffects is shown to fairly well describe the data in its mid range. Explanations for departuresat low and at highfrequenciesfrom the proposedexpressiondescribingthe results aresuggested.

1. INTRODUCTIONWhen the reflective surfaces of an enclosure are not toodistant one from another and none of the dimensions are solarge that air absorption becomes of controlling importance,the sound energy density ofa reverberant field will tend touniformity throughout the enclosure. Generally, reflectivesurfaces will not be too distant, as intended here, if noenclosure dimension exceeds any other dimension by morethan a factor of about three. As the distance from the soundsource increases in this type of enclosure, the relativecontribution of the reverberant field to the overall sound fieldwill increase until it dominates the direct field (Beranek. 1971seeCh,9;Smith.197IseeCh3).Thiskindofenclosedspace,in which a generally uniform (energy density) reverberantfield,characterisedbyamean sound pressure and standarddeviation, tends to be established, has been studied extensivelybecause it characterises rooms used for assembly and generalliving and will be the subject of this paper. For convenience,this type of enclosed space will be referred to asa Sabineenclosure named after the man who initiated investigation ofthe acoustical properties of such rooms.

All enclosures exhibit low and high frequency responseand generally all such response is of interest. However,onlythe high frequency sound field in an enclosure exhibits thoseproperties which are amenable to the Sabine type analysis;thus, the concepts of the Sabine room are strictly associatedonly with the high frequency response. For more on thismalterreference may be made to Bies and Hansen (1995).

2. TRANSIENT RESPONSEIf sound is introduced into a room, the reverberant field levelwill increase until the rate of sound energy introduction is justequal to the rate of sound energy absorption. If the sound

source is abruptly shutoff,the reverberant field will decay ata rate determined by the rate of sound energy absorption. Thetime required for the reverberant field to decay by 60 dB,called the reverberation time, is the single most importantparameter characterising a room for its acoustical properties.For example, a long reverberation time may make theunderstanding of speech difficult but may be desirable fororgan recitals.

As the reverberation time is directly related to the energydissipation in a room, its measurement provides a means forthe determination of the energy absorption properties ofaroom. Knowledge of the energy absorption properties of aroom in turn allows estimation of the resulting sound pressurelevel in the reverberant field when sound of given power levelis introduced. The energy absorption properties of materialsplaced in a reverberation chamber may be determined bymeasurement of the associated reverberation times of thechamber, with and without the material under test in the room.The Sabine absorption coefficient, which is assumed tobeaproperty of the material under test, is determined in this wayand standards (ASTM C423 - 1984a; ISO R354 - 1963; AS1045 - 1971) are available which provide guidance forconducting these tests.

In the following sections two methods will be used tocharacterise the transient response ofa room. The classicaldescription, in which the sound field is describedstatistically,will be presented first and a new method, in which the soundfield is described in terms of modal decay, will be presentedsecond. It will be shown that the new method leads to adescription in agreement with experiment.

2.1. Classical DescriptionAt high frequencies the reverberant field maybe described interms ofa simple differential equation which represents a

Vol. 23 (1995) No.3 - 97

gross simplification of the physical process but none-the-lessgives generally useful results. The total mean absorptioncoefficient a ,includingairabsorption,m(dBperl,OOOm),may be written in terms of the volume, V, and total surface, S,of the room as follows.

a = aw+9.21xlO-4mV/S (1)

Using the well known expression for the energy density,ljJ = (i) / (Pe2) ,where p is the root mean square soundpressure,pisthe density and e the speed of sound in air thefollowing equation may be written for the power, W., or rateof energy absorbed:

W. = ljJSea/4 = (l)Sa/(4pe) (2a,b)

Using the above equation and observing that the rate ofchange of the energy stored in a reverberant field equals therateofsupply,Wo,lesstherateofenergyabsorbed,W.,gives

the following result.

W = va1J1lat = Wo-1J1Sca /4 (3a,b)

Introducing the dummy variable,

X = [4Wo/ Sea]-ljJ (4)

and using Equation 4 to rewrite Equation 3, the followingresult is obtained: I dX Sea

Xdt = -- (5)

Integration of the above equation gives:

X= X oe·,xW/4Y (6)

where Agis thc tninal value.

Two cases will be considered. Suppose that initially, attime zero, the sound field is nil and a source of sound powerWo is suddenly turned on. The initial conditions are time

t = oandsoundpressure(p~) = 0. Substitution of Equation4 into Equation 6 gives, for the resulting reverberant field atanylatertimet,

(/) = 4~;:-(I_e·s,m/4Y) (7)

Altematively, consider that a steady state sound field hasbeen established when the source of sound is suddenly shutoff. In this case the initial conditions are time t= O,soundpower Wo = 0, and sound pressure (i) = (p~). Again,substitution of Equation 4 into Equation 6 gives, for thedecaying reverberant field at later time t:

(P2)= <p~)e·s,ml4Y (8)

Taking logarithms to the base ten of both sides of Equation8 gives the following result.

Lpo-Lp = ID86Scai/V (9)

Equation 9 shows that the sound pressure level decayslinearly with time and at a rate proportional to the Sabineabsorption Sa. It provides the basis for the measurement andthedefinitionoftheSabineabsorptioncoefficienta.

9B-Vol. 23(1995) No.3

Sabineintroducedthereverberationtime,T60(seconds),as

the time required for the sound energy density level to decayby 60 dB from its initial value. He showed that thereverberation time, T60 , was related to the room volume, V, thetotal wall area including floor and ceiling, S, the speed ofsound, C, and an absorption coefficient. trwhich wascharacteristic of the room and generally a property of thebounding surfaces. Sabine's reverberation time equation,which follows from Equation 9 with Ls«: L, = 60, may bewritten as follows

T60 = 55.25V/ScrT (10)

2.2. Modaldescription

The discussion thus far suggests that the reverberant fieldwithin a room maybe thought of as composed of the excitedresonant modes of the room. This is still true even in the highfrequency range where the modes may be so numerous andclose together that they tend to interfere and cannot beidentified separately. In fact, if any enclosure is driven at afrequency slightly off-resonance and the source is abruptlyshut off,the frequency of the decaying field will be observedto shift to that of the driven resonant mode as it decays(Morse,1948).

In general, the reflection coefficient, ~, (the fraction ofincident energy which is reflected) characterising any surfaceis a function of the angle of incidence. It is related to thecorresponding absorption coefficient, o, (the fraction ofincident energy which is absorbed) as a + f3= I. Let (p(t)2)be the mean square band sound pressure leveJ at time tinadecaying field and (p.(t)2) be the mean square soundpressure level of mode k. The decaying field may beexpressed in terms of the sum of the time varying modalsquare pressure amplitudes (p,(t)2), mean reflectioncoefficients ~. and modal mean free paths A, as follows,

(P(tj) = ~(p,(tl)13,"/A' (II)

where

In the above equationsNis the number of modes within ameasurement band. The quantities 13ki are the reflectioncoefficients and S; are the areas of the correspondingreflecting surfaces encountered by a wave travelling around amodal circuit associated with mode k and reflection fromsurface i(Morse and Bolt, 1944). The S.are the sums of theareas of the Sj rcflecting surfaces encountered in one modalcircuitofmodek.

The modal mean free path Ak is the mean distance betweenreflections ofa sound wave travelling around a closed modalcircuit and for a rectangular room is given by the followingequation (Larson, 1978).

A. = 2:'[~+T~J (\3)

Acoustics Australia

(20)

The quantities ~k are the reflection coefficientsencountered during a modal circuit and the symbolIT.I re~res.ents the pr?duct of the n reflection coeffi~ientswlieren ISeither a multiple of the number of reflections m onemodal circuit or a large number. The quantity fk is theresonance frequency given by the following equation for modekofarectangularenclosure, which has the modal indices nx•

n

y

n

z

• r, = f~[~f + [Z-r + [zf (14)

In the above equation the subscriptkon the frequency variablefindicates that the particular solutions or "eigen" frequenciesof the equation are functions of the particular mode numbersnx' ny, and n:.

The assumption will be made that the energy in each modeis on average the same, so that in Equation II,Pkmay be

replaced with PoI.[N where Po is the measured initial sound

pressure in the room when the source is shutoff. Equation 11

may be re:~~;j: f~IO:S~;> i.f dot/h,)los/J-a,) (15)N p ]

A mathematical simplification is now introduced. Intheabove expression the modal mean free path length is replacedwith the mean of all of the modal mean free paths, 4 VIS,andthe modal mean absorption coefficient ak is replaced with theareaweightedmeanstatisticalabsorptioncoefficienta"fortheroom. The quantity Vis the total volume and Sis the totalwall,ceilingandfloorareaoftheroom.lnexactlythesameway as Equation 10 was derived from Equation 8, the wellknown reverberation time equation of Norris-Eyring maybederived from Equation 15 giving an expression as follows.

T.-~ (16)60 SclogJl-a,,)

This equation is often preferred to the Sabine equation bymany who work in the field of architectural acoustics. Notethatairabsorptionmustbeincludedina"inasirnilarwayasit is included in a. It is worth careful note that Equation 16is a predictive scheme based upon a number of assumptionsthat cannot be proven, and consequently inversion of theequation to determine the statistical absorption coefficienta.,isnotrecornrnended. With a further simplification, thefamous equation of Sabine is obtained. Whena,/ < 0.4, an errorof less than 0.5 dB is made by setting a,/ .Iog.(l-a,/)in Equation 16. Then by replacing a,/with a, Equation 10 isobtained.

Alternatively,ifinEquation 15 the (I-ak ) are replacedwith the modal reflection coefflcients s, and these in turn arereplaced with a mean value, called the mean statisticalreflectioncoefficient"iJ./,thefollowingequationofMillingtonand Sette is obtained.

Too = -55.25VISc1og.i3" (17)

The quantity "iJ.,isgivenbyEquation 12 but with changes inthe meaning of the symbols.f', is replaced with "iJ.,whichis

Acoustics Australia

now to be interpreted as the area weighted geometric mean oftherandomincidenceenergyreflectioncoefficients,~i,forall

of the room surfaces; that is,

iJ,,-Of:l,s,1S (18)

The quantityfl.js related to the statistical absorption

coefficienta",i for surface i of areaSI by f3i = I-a",. Itis of interest to note that although taken literally Equation 18would suggest that an open window having no reflectionwould absorb all of the incident energy and there would be noreverberant field, the interpretation presented here suggests

that an open window must be considered as only apart of thewall in which it is placed and the case of total absorption willnever occur. Alternatively, reference to Equation II showsthat if any term f:li is zero it simply does not appear in the sumand thus will not appear in Equation 17 which follows from it.

3. NEW ANALYSISWhen a sound field decays all of the excited modes decay attheir natural frequencies (Morse, 1948); the decay of thesound field is modal decay (Lawson, 1978). In the frequencyrange in which the field is diffuse it is reasonable to assumethat the energy of the decaying field is distributed among theexcited modes about evenly within a measurement band offrequencies. In a reverberant field in which the decayingsound field is also diffuse, as will be shown, it is alsonecessary to assume that scattering of sound energycontinually takes place between modes so that even though thevarious modes decay at different rates scattering ensures thatthey all contain about the same amount of energy on averageduring decay. Effectively, ina Sabine room all modes withina measurement band will decay on average at the same rate,because energy is continually scattered from the more slowlydecaying modes into the more rapidly decaying modes.

Let (p(t)2)be the mean square band level at time t in adecaying field and (p(O/) be the mean square level at time t

= O. The decaying field may be expressed in terms of a timevarying mean square pressure amplitude p(t)2, modal meansquare pressure amplitude Blt), mean reflection coefficient ~i

and modal mean free paths Ai' Equation II may be rewritten

as follows. (p(tl) = (p(O/) ~ BP)f3~tfA,MY ~, (19)

In the above equation the number of modes within ameasurementbandboundedbelowbyN] and above byN] isMY. The reflection coefficient f3i is given by Equation 12. Itwill be noted that Equation 19 is the same as Equation 15 withthe exception of the introduction of the modal amplitudesB;(t).

It may readily be shown (Bies, 1984) that when areverberant field is diffuse the mean of the modal mean freepaths,Ai, is the mean free path of the room given by thefollowing expression (Morse and Bolt, 1944).

A= ~S

Vol. 23 (1995) NO.3 - 99

Sabine observed that in a room in which the sound field isdiffuse decay of the reverberant field is a linear function oftime whatever the initial level when the sound source isabruptly shutoff. Sabine introduced an absorption coefficient,a,,", ,which is generally a property of the walls of the roomrelating the change in sound pressure level and the length oftimeofreverberation,t. Forconvenience,aroominwhichthesound field is diffuse and reverberant sound field decay is alinearfunctionoftimewillbereferredtohereasaSabineroom (Fasold, Kraak, and Schirmer, 1984). The roomreverberation decay may be written in terms of the room meanfree path A and the Sabine absorption coefficient a basfollows. !£!!.iJ.... _ ct sa

10g,(p(O/) - -'Aa,ab (21)

It will be instructive to consider first the decayofa singlemode as given by Equation (19). In this case letting AN = I,i =j and B, = I Equation (19) may be rewritten as follows.

10g,¥1f!f = -J!;log.f3; (22)

Alternatively, ifin Equation (22) (3) = l r a, where a) issmall then

Substitution of Equation (23) into Equation (22) gives anequation formally the same as Equation (21). Evidently. in aSabine room reverberant sound field decay is formally thesame as that for any individual mode. Consequently, it will beconvenient to extend the meaning of Equation (23) to define aSabine reflection coefficient, {3,ab' and to define the relation­ship between the Sabine reflection coefficient and a Sabineabsorption coefficient. Reference to Equation (22) suggeststhat the associated Sabine reflection coefficient is a meanreflection coefficient of the excited and decaying modes of theroom.

Solving Equation (21) for the Sabine absorptioncoefficient, a,ab' and introducing Equations (19) and (23)

gives the_~:::;::g ~P~~ts:::: [-b~ BI(t){3,cIJAi] (24)C UIYj-NI

The following Equation is o~~ained from Equation (24).

f3,abdA= -!:-N~,B,(t)f3/IJ'" (25)

Consideration of Equation (25) shows that in generalf3"bisa function of time, and the reverberant field decay willnot be linear with time. For example, consider the case that allBi=1 and no scattering of sound energy between modes takesplace during sound field decay. Ifat time zero the amplitudesof all modes were approximately equal and subsequently themodes have all decayed independently of each other, thosemodes decaying most rapidly will determine the decayingfield response initially while those modes decaying leastrapidly will progressively dominate the remaining reverberant

100-Vol. 23(1995) NO.3

field response as the field decays. The latter effect is observedexperimentally in a reverberant room unless sufficientdiffusing elements are introduced in the room. Consequently,it is necessary to introduce the effect of scattering of soundenergy from those modes more highly excited to those modesless excited.

Ina Sabine room, however, experience shows that {3,abisaconstant independent of time. For example, Equation (25)may be rewritten as, Aiel

«: = [tv%/Bi(3) ctJAi] (26)

Consideration of Equation (26) shows that in order thatthere be a solution itisnecessarythatall terms in the sum onthe right hand side of the equation must be equal and in turneach must be equal to the term on the left hand side of theequation.

In the model which has been proposed it is assumed thatsound energy is removed from modes least damped throughscattering upon reflection at the boundaries and introducedinto modes more heavily damped. The amplitude coefficients,Bi, of the latter quantities will be greater than I while theamplitude coefficients of the former quantities will be lessthan I. Further consideration of Equation (26) shows thatthere will be some modes which will be unaffected by theassumed energy exchange and in their case the amplitudecoefficients are I. For such modes the above considerationslead to the following conclusion.

(3,,", = f3:J", (27)

Ifitis assumed that the unaffected modes are the modeswhose reflection coefficients are the mean of the modalreflection coefficients then it is reasonable to assume that themodal mean free paths are also mean values of the modalmean free paths. In this case the Sabine reflection coefficientis simply equal to the modal mean reflection coefficient.

f3,ab = f3modalm,an (28)

The modal mean reflection coefficient has the form givenby Equation (12).

Consideration of Equation 23 suggests the followingrelation be assumed to hold for all values of a,ab and 13,abThat is, it will be assumed that Equation 23 constitutes a

definition of a ''"' in terms of f3"b'

a"b = -log,13,ab (29)

Substitution of Equation 29 in Equation 22 leads to thefamous equation of Sabine as follows.

55.25VT6tJ = Sea,,", (30)

The important difference in the equations derived earlierrelating the Sabine absorption coefficient and thereverberation time and Equation 30 is to be noted. Althoughthey are formally identical the earlier expressions are all basedupon a number of assumptions which can not be proven whilein the latter case the only assumption made is that Equation 23

f(Hz)100 0.Q7 0.11 0.11 0.10 0.16 0.1125 0.26 0.24 0.23 0.21 0.22 0.17160 0,33 0.32 0.34 '0,33 0,35 0.22200 0.49 0.50 0.50 0.51. 0.52 0.31250 0.67 0.68 0.68 0.68 0.67 0.41315 0.86 0.90 0.88 0.88 0.82 0.52400 1.04 1.00 0.97 0.96 0.92 0.64500 \.14 1.09 1.04 1.01 0.98 0.74630 \.15 \.14 1.10 1.06 1.05 0.81800 1.16 1.13 1.08 1.07 1.08 0.861000 \.17 \.14 1.09 1.05 1.07 0.901250 1.15 1.08 1.07 1.03 1.07 0.911600 1.12 1.06 1.05 1.02 1.05 0.922000 1.07 1.06 1.04 0.99 1.03 0.932500 1.10 1.07 1.04 1.01 1.03 0.943150 1.07 1.08 1.05 0.99 1.06 0.944000 1.08 1.08 1.05 1.01 1.08 0.945000 1.12 1.06 1.05 1.00 1.08 0.94

Use of the data in Table I has allowed construction ofFigure 1. In tum the figure has allowed determination of anempirical function F(P'c/Aj) which seems to fairly welldescribe the data. The empirically determined relationship is,

(~-1)= ~ (34)X

where

A principal conclusion of the latter report was that thoserooms with auxiliary diffusing surfaces equal to or greaterthan 1.4 times the floor area of the reverberant room gaveresults consistent among themselves whereas those roomswith less or no auxiliary diffusing surfaces gave results whichwhere inconsistent with all other rooms. Seven rooms rangingin volume from 106 to 607 cubic meters were identified asmeeting the diffusing surfaces criterion which gave consistentresults for samples ranging in size from 5.0 to 22.5 squaremeters. Sample sizes were chosen consistent with the size ofthe room and a sample ofl0.5 square meters was tested in allrooms. The data obtained in the latter seven rooms providesthe basis for a comparison with prediction.

The referenced report provides four measurements ofa 5.0m2 sample, six measurements of a 7.5 m2 sample, sevenmeasurements of a 10.5 m2 sample, three measurements of a16.0 m2 sample, and one measurement of a 22.5 m2 sample inall one third octave bands from 100 Hz to 5,000 Hz. For thepurposes of the proposed comparison average values havebeen determined and recorded in Table I. Also recorded in thetable for convenience of later comparison are calculatedvalues of the statistical absorption coefficient. The statisticalabsorption coefficient is shown for an infinite locally reactivesurface. However, calculations for a bulk reacting surface areonly slightly greater at frequencies greater than about 2000 Hzand thus the difference between the two types of surfaces isconsidered negligible.

Table I. Absorption Coefficients

is true. As will be shown the Sabine equation given byEquation 30 leads to agreement between measurement andprediction when edge diffraction is taken into account in thedetermination of the Sabine absorption coefficient.

4. CALCULATION OF THE SABINEABSORPTION COEFFICIENT

It is customary, following Sabine, to calculate absorption asproportional to the area of an absorbing patch of material. Onthe other hand, where there is a large difference in surfaceimpedances between the absorbing patch and the adjacent wallor floor on which it is mounted, as in the case of the usualreverberation room test, large diffraction effects will takeplace which in the case of the reverberation room have theeffect of considerably adding to the effective area of the patch(Morse & Bolt 1944). Where Ap is the physical area of thepatch and A e is the effective additional area due to edgediffraction the Sabine absorption may be written as follows.

Apa"b = aro(A p+ Ae) (31)

In the above equation ambis the measured Sabine absorptioncoefficient and a¥is the calculated statistical absorptioncoefficient for an unbounded surface.

Various authors have considered the calculation of theeffective area Ae (Pellam 1940, Morse and Bolt 1944, Levitasand Lax 1951, Northwood et al. 1959, Northwood 1963) withvarious degrees of success but none are convenient to use andonly that of Northwood considers the rectangular patch asconsidered in the CSIRO tests which will be considered here(see below). The approach which will be taken will beempirical but guided by the observations of Morse and Bolt(1944) and will be limited to showing that a consistentrelationship exists between the measurements and theorywhen diffraction is taken into account.

Following Morse and Bolt (l944) the effective area will beassumed proportional to an effective perimeter of the patchP'= P - a, where P is the physical perimeter and a is a con­stant that is assumed to account for the comers of the patch,multiplied by a wavelength written in terms of the speed ofsoundcandfrequencyfasc/f. Equation 31 gives the follow­ing postulated functional relationship which will be shown

emPiriCallytoexist('~_I) =F(.5!:....) (32)

a~ Apf

5. COMPARISON OF MEASUREMENTSAND THEORYIn 1980 CSIRO-Division of Building Research published areport describing the results of around robin conducted inAustralia and New Zealand in which the Sabine absorptioncoefficients of samples of Sill an were determined using thestandard reverberation decay method (Davern & Dubout 1980).Inall,twentyonereverberantroomswereinvolvedinthetests.The test material, a rock wool batt material of density 100kg/m- made by Grunzweig-Hartmann of Germany, was similarto that used in an earlier round robin in Europe (Kosten 1960).

X=~c(P-3.55)

(35)

Acoustics Australia Vol. 23 (1995) NO.3 - 101

0+--------'-------+........-><-L-----'--'---'--'-+--______L__~_ ___'____'_____L___'___1

0.1

Plotof measuredand normalizedsabineabsorptioncoefficients(Table1) as a functionof normalizedfrequency(equation35.) See text fordiscussion.

Consideration of the figure shows generally goodagreement over the decade range of the parameter X fromabout 1.0 to,about 10. Above 10. one would expect the edgecorrection to diminish to zero. It is suggested that the evidentdeparture from the latter expectation at high frequencies maybe due in part to the discontinuity in height at the edge betweenthe surface of the absorptive patch and the concrete floorwhich increases as the ratio of sample thickness to wavelengthincreases. This has not been considered in any analysis.

Departure at the low frequency end is probably due tofailure at long wavelengths of the reverberant rooms to meetthe conditions for a diffuse field implicit in the Sabineformulation. At very low frequencies the wide scatter is dueto the difficulty of making the necessary reverberationmeasurements with sufficient accuracy. However, even thoughthe data become quite scattered as the frequency decreases agenerally consistent trend can be identified suggesting thepossibility of an analytic solution.

6. CONCLUSIONAn analysis has been presented which shows that the Sabineequation is correct if it is accepted that the mean modalreflection coefficient and the statistical absorptioncoefficientare related as proposed. In support of this conclusion therelationship between the calculated statistical absorptioncoefficientofanunboundedporousmaterial,Silan,andthemeasured absorption coefficient has been demonstrated in thecase that adequate diffusion has been achieved in the testchambers used for the measurements. The demonstration hasshown the importance of adequate diffusion and edgediffraction for the determination of the sound absorptiveproperties of a test material in a reverberation chamber.Conversely, by implication the importance of diffusion and

102- Vol. 23 (1995) NO.3

edge diffraction for application of absorptive materials inaSabine type room have also been demonstrated.

For application to the practice of room acoustics aquantitative measure of diffusion is required which besidesidentifying adequate diffusion would also identify degree ofpartial diffusion (Bodlund 1976, 1977a,b). In tum, furtherinvestigation is required to determine the quantitative effect ofpartial diffusion on sound absorption so that it may be takeninto account in practice. Additionally,simpleproceduresarerequired which will allow estimation of the effect of edgediffraction on sound absorption (Pellam 1940,MorseandBolt1944, Levitas and Lax 1951, Northwood et al. 1959,Northwood 1963).

REFERENCES

3. Bies, D.A.andHansen, C.H. (1995)Engineering Noise Control secondeditionChapman andHall(inpress)

5. Bodlund,w'(1977a)AStudyofDiffusioninReverberationChambersProvided withSpecialDevices. Journal of Sound and Vibration 50(2),253-283.

6. Bodlund, W, (1977b)A NormalModeAnalysis of the SoundPowerInjection in Reverberation Chambers at Low Frequencies and the EffectofSomeResponseAveragingMethods.]ourna[ojSoundandVibration50(4),563-590.

. Faoold,W. KtMk. W.llndS"',;....... W. (l9 ..)T~Jlb,oliol.

VEB....... I. Bnt .... pIOJ9, ¥.ooIaI, C.W, (1960) l"' .......~ C__ Io!__. ...

R.-hcntioIlR-... JlnlSIkoI l l . 400.

10. Kuuull",H.(l99<l) SoUIIddeay in e"" luo.nowilhllOlHlil'l'iloelOlltldfield.ln ~i",. "" II< Iti>Is...-. CI•..,.t S4b; ... ~"...

c.mm•• MA. mlA. IS-II

II.=-~':"71~~_ II ...... r--o.hoo' 01 .-.-12.~A.,l:Lu.N.( I95 IIx......,.."""A~tIl'._

SIrip , ..........__ """""._na~JI...l2Z

Il .~~H~i (1941) I'iM_ 211d.. ""'" V.....

14. Nont. PM " 8011. Il R (I'loM)SouM oa-. 1._.u-..1'1".,a 1"6S-1~

U.-........T.D..GriYno,NT. .. Mcodcol"."'.A.- (lm)A~.

s.-d "" . sw,..A-,..o \4.-..1 ;"' . Dill\toc s-..I F..iIl.Nw-I."__~"JI_Jl (1), m-S99.

IlL --... T.D. (I96JJ~.Di",*,s-.:ItIl'.Sonp......,..,....,......~M.enoI,.J--l•• _s..e;"y"'JI_ lJ (I ),Il1)_II n.

11.~ l L ( IMO) s.-d DilJrlellool... A-"- by I Srop •:=IM-...t"""''''IA# ~s..e;"y -lJl_ l l .

l · s.ido, lUtlt1 I)~~ ......,...

ENVI R ONMENTALNOISE CONTROL~

YOUR SOLUTION TOINDUSTRIAL NOISE PROBLEMS

MANUFACTURERS OF ACOUSTIC• Louvres · Doors · Enclosures

• Silencers & Steel Fabrications

SUPPUER$OFEOUIPMENT FOR:

PROJECT: SLIDING ACOUSTICDOORS

CONSULTANTS: ACOUSTICLOGIC

ClIENT: TECHPACIFICP/L

Phone: (02) 755 107750 RIVE RSIDE ROAD

CIII PPING NORTON, N.S.W. 2170

1I11It~ry "....rlll. d IOJ:l".,.nlfK" rJ'"rlll i nll,,,l'I wll~lod uwn·I""d<l "l a lnln }'ollr rnmpute r.

Complde ly wealher pruur lllMI ' Ul:l:ed .

ConllK·l lL,r", inrurtn llli" n.

\0\:)1 . 23( 1995) "10.3 · 103

RION Integrating Sound level Meterxt-os

Meet s tsc typ e 2Preset Measureme ntsMax. 50 Leq. data storeSimple OperationUnderI Overload DisplayInternal Mem ory andPrin t Out for Leq Data

Why Choose BEASYTHE SECOND GENERATfON ACOUSTfC SYSTEM

• Measures Lp.Lmax,Leq, L AE

• 29-130dB

• 6Ra ngl"s• A,C , Aal

• Freq. Range• 2O-8,OOOfu

• RS-232C• AC&DC Outp uts

• SYDNEY P!1(0213&t 17n F... (02) &47 15-'5. MELBOURNE Ptl (03)9883 8100 F." (03) 9888 0280• BRISBANE "" (07) 381831 1 F... (07) 8$ 1 5e03e ADI!L..AlDI! ""(08) 3"'0588 F"' 108lm n MeP EFml PlI (09j4 79 4766 Fax (09) " 79 _

BEASY Acoustics II a compreheosNe lIimlAlion I ys lem lor 30 IICOOAtlcI moOe lling, Devel oped by experll In Bound8ly EIem EKllstechnOlOgy ~ provIdM noIsecootrol and s trueturlll eogirleflfS powertUeasy 10 use 100ft b simulRling lIC:OUSti~ ptOblem$ lifld IM nlofy;ngnoise cOI1lrol solutions

BEA$Y it lrul lelldil'lg system in it, calegoty wil/'lcompanies W(l(1(lwlde using tile system lorfeal industrial aeoutl~c problems 00 1\ daytoday basi'

Comprehensive d'agMostiCcapabilibes within BCASY Acoustic slOWIhe U&&r to determine the source of the sound rnell5U1ed111 anypoint wil t"O"the acoustio mooe1 and to iderlli !y tha main contributions 10 \h I! sound InteflSily. Th\.ls prOYidl" g all the in!orm aliol'lr>ecessary fol'a rap;d andeffeetive noiSllooot rol atrategy,

BEASY inler1aees feadily' with FEM B'>dBEM modeIIir>gsystems

BEASY provide s powerful ti"ks to CAD wtl ieh enables mooels 10be 001"automafieany.

BEASY pfovldes a dedicated easy to jaarn anc straighlfofw ard to use Imefaelive graphlOS based system lo f model ger>eretiorl andvisuaiisat ;onotf8SlJIS.

BEASY 1'1..'" specially dev8lopll d Intlrlltce$ to allOw \llIpef lmeotal cereon tu rface veloeibeslo be used asdata

BEASY enables vi!)fating SIfI.JCl\l,a! sur/aces to ba accurately modelled, Both me II&loeitya" d impedance of tho sUl'!llce earl besped~ed, along wlth pol" t 1Ir>dII" e SOUfCes

All Acoustic proper\Jes and aP!lhed CO"ldrtionscenhaYe felll and comple~ CXIII'lpol'lel'llS

Mu" iple ececsue'8 g10l'l1 oan be mode~ed to reprllWlfll probllms combi....ng materIals afld nuk\$ Wl\I1differing acoustic properties

Infinite fl glorlS. ;l'IterlOf,eKl erior Brld COI.lpledptoblems ea" be simpled modelied

_i;!!f@M

104 -Vol. 23 (1995) No. 3

Compu fBtlon .1 M8Ch.nln Au.rr.I..I. Ply LIdUnit 1" 4 · 8 QUINn Str ll efBENTLE Y WA 8102PhOllIl :09350 lflf7SF• • : 09 461ISS9

Acoustics Austra lia

Notes on Office Acoustics

Barry MurrayWilkinson Murray Pty LtdSYDNEY NSW 2006 AustraliaMember Firm, Australian Association of Acoustical Consultants

Abstract Based on theoretical aspectsof acousticsand years ofe xperience,practicalmethods of office acousticdesign have been determined. When installingpartitioningfor cellular offices,care needs to be taken to ensurethat the sound transmissionloss of the partitionconstructionis matchedby surroundingconstructionsand details.When designing open office plans, a careful balanceof all of the factorS,includingsoundabsorption, distance,shieldingandbackgroundnoiselevel,isrequired. Theacousticdesignofconferenceroomsmustalsoallowforthe modem audio technologyassociatedwith such rooms.

1. INTRODUCTIONThis paper discusses some acoustical aspects of modernoffices. It is intended to summarise some of the conclusionsthat have resulted from years of experience of the acousticaldesign of office spaces. It is not intended to be fullycomprehensive and the technical basis for some of theconclusions is also not discussed in detail.

Changes which have occurred over the last decade or so inthe way offices work have changed the acousticalrequirements of office spaces. Such changes as the extensiveuse of computers, the introduction of audio visual facilitiesinto Conference Rooms and the more common use of Tele­Conferencing and Video-Conferencing facilities. ThisTechnical Note discusses both the acoustics related to therecent changes and conventional office acoustics. Inparticular, office partitioning, open office plans andconference rooms are discussed in some detail.

2. OFFICE PARTITIONSTo allow flexibility within office spaces, it is common toprovide office partitioning using dry construction, as opposedto brick or concrete block. Where acoustical performance isrequired, the partition is often a stud and plasterboardpartition. Such partitions allow medium to good soundtransmission loss performance and overall acousticalattenuation in the speech range. This is achieved ata lowweight to performance ratio, compared with such materials asbrick. Details of plasterboard wall sound transmission loss arereadily available from plasterboard manufacturers.

However, where a plasterboard partition is used toseparate spaces in an office, the transmission through thepartition is not the only noise path to be considered. Noisecan also be transmitted up through the ceiling and back downagain in the adjacent space as well as through any poor sealsat the junctions. The main noise paths are demonstrated inFigure 1.

Acoustics Australia

Figure 1. Noise Transmission path through and around anOffice partition(section).

Whilst itis relatively easy to obtain good seals through theplasterboard wall at the joints of sheets of plasterboard (sincemanufacturers have standard taping and setting methods),seals to the ceiling and to window mullions are often difficultto achieve. To maximise the flexibility within office spaces,builders are reluctant to use good acoustic sealants (such asMastic) between the head of the partition and the underside ofthe ceiling. Often standard foam strips are used and, whilstthese provide better seals than can be provided without suchstrips, good airtight seals are not possible. This problem isaggravated by the types of acoustic ceilings commonly used inofficespaces,suchasmineralfibreceilingtileslaidinagridor perforated metal pan ceiling tiles also laid in a grid.

It is also common to find poor seals between officepartitions and window mullions, where such partitions extendto the building perimeter walls. The expansion and contractionof the window mullion, especially where it is exposed to directsunlight, tends to crack a standard plaster seal. It is thereforenecessary to use a sealant with a degree of flexibility in thejoint, such as a non-setting Mastic or a silicone sealant. It alsofollows that the end of the partition abutting the external wallneeds to be constructed so as to follow the profile of the walland to take account of the window sill and any otherconstruction above and below the window.

Vol. 23 (1995) No.3 - 105

a500 1000 2000 4000 8000

sr40

Figure2. SoundTransmissionLoss for llOmmbrickwalland16mmplasterboardeach side of 64mm steel studs with 50mminsulationin the cavity(STC44).

30IdS)

20

3. OPEN OFF~CE PLANSWhen developing open office plans instead of cellular offices,one of the most difficult features is establishing sufficientacoustical privacy between workers. The success in thisregard depends upon a number of factors:

• Sound absorption in the space.

• Distancebetweenofficepersonnel.• The degree of shielding between personnel.

• Thebackgroundnoiselevel.

Sound absorption is most commonly provided by the useof an acoustic ceiling. The perforated metal pan ceiling tilewith sound absorbent insulation above provides the bestavailable ceiling absorption and this leve1 of absorption ishighly desirable. However, the most common form of acousticceiling within modern offices is the mineral fibre ceiling tile.Its sound absorption coefficient is less than the perforatedmetal pan tile, but it can prove an acceptable compromisee.

Other reflective surfaces, particularly walls, can affect thetransmission of sound throughout the open office space.Open plans therefore work best in large areas where reflectivewalls affect a limited proportion of the office personnel. Onthe other hand, it is possible to apply sound absorption toreflective walls. Over and above this, all screens to be usedwithin the space should be the sound absorbent type and thislimits the selection to a small proportion of commerciallyavailablc"acoustic" screens.

Obviously, the further apart that office personnel are, theless likely that a lack of acoustical privacy will occur. Inpractice,adistanceof3mbetweenpersonnelorientatedback-

those low frequencies. Accordingly, stud/plasterboardpartitions can often result in low frequency noise transmissionfrom rooms with audio-visual facilities to adjacent rooms and,for larger conference rooms, brick construction or heavyplasterboard construction is often required. One should beaware that STCperformance does not give a true indication ofthe overall subjective performance in many instances.

In respect of sound transmission from room to room viathe ceiling space, the ceiling material needs to be selected sothat this path does not become a weak link in the system.Most major ceiling manufacturers have had their ceilingstested to provide room-to-room sound transmission lossperformances. For common mineral fibre ceiling tiles, thesound transmission loss is normally in the vicinity of SoundTransmission Class (STC) 35-40. Such a performance isadequate for most standard office partitions, but some form ofupgrading is required where a high standard office partition isneeded, such as STC40 or 45. The best way of upgrading theceiling performance is to install a vertical baffle extendingfrom the ceiling to the underside of the slab above to providea third barrier between the two rooms via the ceiling. The thirdbarrier is normally so effective that only a single layer ofstandardbuildingmaterial,suchasplasterboard,isnecessaryto substantiallyimprovetheroom-to-room sound transmissionloss.

Care should be taken where perforated metal pan ceilingtiles exist within the building. Although these tiles commonlyhave insulation laid over them, they are almost transparent tonoise. Accordingly, sound transmission loss via the ceilingspace is substantially below that of a low performancepartition. This problem can be overcome by again installing abaffle within the ceiling space or, alternatively, by fixing asolid material to the back of the tiles (such as singleunperforatedmetal).

Improving the room-to-room sound transmission loss viathe ceiling space by the installation of baffles or by backing oftiles will have no effect upon the quality of seal between thepartition and the underside of the ceiling. This weakness oftenlimits the performance of office partitions unless the partitionextends through the ceiling, preferably to the underside of theconcrete slab above.

Whilst the most critical partitions within office spaces arethose that separate individual rooms, such as two offices, twoconference rooms or an office and a conference room,partitions separating such rooms from corridors can also be ofsome acoustical importance. However, these walls are oftensubstantially weakened by the installation of doors for access.Since a good solid core door with acoustical seals is unlikely toprovide more than STC 30, no benefit is gained by installing apartition with a sound transmission loss greater than STC 40.In fact, little benefit is gained by installing a partition with asound transmission loss of greater than STC 35.

The frequency characteristics of plasterboard partitionsound transmission loss performance need to be considered insome circumstances. As demonstrated in Figure 2, the STC ofa stud/plasterboard partition with insulation in the cavity canbe as good overall as a single brick wall. However, the soundtransmission loss performance in the low and high frequenciesis less than that for a brick wall and the low frequencyperformance particularly can prove important where audio­visual facilities are to be installed. Since all partitions andwalls are weaker in the low frequency bands, it can beimportant to maintain the highest practicable performance in

106 - Vol.23 (1995) NO.3

to-back will prove adequate, but greater distances arerequired where the personnel are face-to-face. However,shielding by office screens can provide the required privacy atmuch reduced distances.

The shielding is best provided by free standing screens orscreens which form part of work stations. The line of sight

I between the heads of office personnel must be clearly broken, to ensure significant reduction in sound transmission occurs.I This means that the screens should be ofa height of at least

1.5 m above the floor. Such screens can then reduce theminimum distance between office personnel orientated face­to-facetoapproximatelyI.5m,dependinguponotherfactorssuch as sound absorption and background noise level.

Most office spaces have a background noise levelgenerated by operation of the air-conditioning system. Thisbackground level can mask the intrusion of sounds fromnearby office personnel, thereby reducing the intelligibilityand increasing the acoustic privacy. The background noiselevel is best when sufficient in level andofa spectrum shapeto provide good masking, whilst at the same time beingsubjectively unobtrusive. Figure 3 sbows a range ofbackground noise levels which appear to have the correctbalance between masking and unobtrusiveness. Forconvenience the RC curve (say RC40) may be used as anapproximation, although the shape of that curve is not tunedto provide the fine balance that is often necessary.

~:~S~~~_t!=::=..~(d8) 30

°6L-3 ---:-:-'--:-::-:---10-00-2-00-0-4-00-0-'8000 0

Figure3. SuggestedBackgroundNoise Spectrum.

Air-conditioning systems can be used to specifically createa background noise level similar to the type required for anopen office plan. The air outlets can be adjusted ordamperedback to provide approximately the correct level and spectrum.However,thismethodisrelativelyunreliableanddoesnotgivegreat flexibility in setting the spectrum shape.

The best way of providing the background noise level is bythe use of an electronic system. This system commonlyincorporates a noise generator, agraphic equaliser, anamplifier and a series of loud speakers installed in the ceilingspace. The method of installing the loud speakers in theceiling space is important in obtaining a good spread of soundthroughout the space. Since loudspeakers are quite

Acoustics Australia

directional in the high frequencies, loud speakers mountedbehind standard loud speaker baffies within the ceiling give asubstantially different spectrum shape directly under than toone side One of the best ways of overcoming this, whilst atthe same time providing a well rounded unobtrusive quality ofsound, is to mount the loud speaker above the ceiling tile andallow the sound to be transmitted through the tile. Figure4shows a successfully used system for offices containingmineral fibre ceiling tiles.

Figure4. Suggestedloudspeakermountingdetail for a mineralfibre ceiling.

4. CONFERENCE ROOMSThe acoustical design of conference rooms to provide a higherdegree of intelligibility is widely understood by acousticians .However, the extensive use oftele-conferencing and video­confercncing in today's conference rooms changes theacoustical characteristics required within the room. Thesesystems commonly use microphones which are often locatedat some distance from the person speaking. Under thesecircumstances, many existing conference rooms will generatequite reverberant sounds for the receiver at the end of theconference transmission line.

To overcome this, the conference rooms should bedesigned to be relatively dead acoustically. As a general rule,small conference rooms work relatively well where there isgood carpet on the floor and an acoustic ceiling over.However, some sound absorption on wall areas will improvethe overall performance.

For larger conference or seminar rooms, a more detailedanalysis of reverberation times is required. These roomsshould be designed as if they are low standard sound studios(where this is practicable) and it is suggested that areverberation time somewhere between that recommended fora room for speech and a talk studio would suffice.

5. CONCLUSIONToday's office building occupants are demanding a higheracoustical standard within their offices than they did twodecades ago. Acoustical privacy, whether within cellularoffices or an open office plan, is the over-riding requirement.With the new office audio-visual aids, providing this privacyis getting harder and harder.

Vol. 23 (1995) NO.3 - 107

AUSTRAUAN ACOUSTICAL SOCIITY1996CONfER!NC!

'......~,....,."15 \1l~m'.~

'0McUg""" .....,.....d1e;sla!kla.1.- _

1...-=1011M~~(01) :lI~ I'"..c.llor ...".."d ll. ... ... _

l.4etteu... II write in IODickBcnbow'spc<p lningproblem r' Nmc" ACOUlllics Aus1Jalia Aug9' ). IlWO\l.ld>mn fromIhe p<ccise lol;olionortbe no~ lIUiAIKc thal we ~ dealinl witll

an intflferm<c ell"ect ;n ) dimensi oos , 'Thehomc, . ffected m obvinw ly .t anti.no<\eso n!he inlenerence patlcm

How lhen is tbe inc~ in freqllll:ncy lO be

uplained! lwouldsuggclt aoeconddiffrac­lion pontm ftom I much 1CMt'T ftequcncynoisoewith aooino;idcnlanti_IIOIk.This rruy be.ub-....ic. llmI)' begmcT81edby a di tf=nlme<:hanism, from. di fferent amy clem ent,froma diffettnt 5lnIeture. MYlluessis th. t thel«ond noise'M)U)d.I "'bc. ...ind-<hivm

If Dickwams to re>l easy IIni ih t, hc:IMYfinda nOl:rurnal excursion on a windy nillht wilhappmpriaICequipment woc'1hwhile

1..'~1 CI..IlerlN<:f. M,US

11if,;~...

n.. followinll are new mom"" ... of theSociety or members who." grading hnchanged

Mcmbu : Mr G J Olllen (SA),Mr M A loch elso n (NSW)

Sl udnt: Mrs 0 Davil (SAj

• Noise, Weather & Vibration Loggers

• Sound Level Meters & Ca/jbrators

• Entertainmen t Noise Contro /lel'S

• BlaM & Piling Digi tal Seismogruph.~

• Equipment lI ire Service

• Permanent ,HonirorinF:Networks

• Noise & Vibration S u rvey Servien

265-271 PernlnlH'III FldThornlelllh tjs w 2120 "' lIIlnI lili

_: llXll_='=~":...-:

Wef}:'~h3~: ~:~~r:~, l'IOftot:(a.)U• • U I ' ... lollIlo: (OI. :IZ1 _

..... 1: aau. 0C0d_ """""

PTV lT O

Sound Absorptionf"

Reverheration and Noise Level ReductionArchitectural CeilingFinish PLUS

Wall Panels Suspended Baffles Acoustic CeilingTiles

M"'~ (03) 959& 5898 Sydnrf (02) 891 3899

108 · Vol. 23 (1995) No. 3

I ~ ~... INSW ME ETIN GSOccupationa l Noise andHear ing LossTbeNSWDivision '&third meClinlfor 199 5.held .t IheN AL . udillll'iurni nC hat"""OOo n~oday2)Augu5t,gavc .n O\'e....iew andupdate of reCent development s in lheoccuplIlion.alnoi.cand hearins loss iooll5try.The m« tins was very ~1I.nended withabout 7S (perhaps a reeord?) 10 hear thepanc l "rs sp•• k. ... Th• • udi.nce comprisedl>arTislCrs• ..,l icito r.;, ludiologilll"COU.li•• 1con .uhants, fe • • arch . .. , membe rs ofinsuraece and employer group' andI """ mment organisations. as well •• oomcindivid....I, with . personal interes t. II i.estimated that at least ha lf o f 1M audienuwufromou!SidctMllOI:ie!y.

K.a !'lllld, of ~ woo..O\ er Authoriry of

:-S W pnnridcd • sU\:cin<;t outl ine ofWori<~\roI.andrcspomibiljli• • wbi. bindlldn its function as Wlde<Wfiler10 theWorkers' Compensation insuranc<: industry.II. , I"" p "• •tati stics and 11"(:n.d. Oft the_rity o(oc cupat ional hearinll lon ;n NSWinelud ios figu res on lh. numbe rs ofcompcn$llion claims made peeyear, overanfin lnci l l co.t and breakdown. of OlherfI ClO...uchu l ge. gende l, type. ofoccupation IIId indus try.

Dr Joh n :o,"'en.f . of Am lralilUl llel rin;Serv icel and Chairpenon. Standard ,Steerin; Comm in « AV/J. pll'st nted I noutline of lC«n tn:5elrchonthe lCcuracyand n:liability of hearing lou lmI$ lIRmcntlIMthods, emph..i,in g <he nm for ",pi..on'll0inlludiomctri c lestini of employecf.lIe dilCUUed <he usc o f shon lerm hcarinaUvcthold shin mcl5lllCmcnlS as l melUl. ofdetermin ing thedfectofoccupationalnoi.eupon employee heari na: lo.s , He I lsoe~amiJlCd whi t appeared to be a novelIpp~htodctenniningtheonsclofhcaring

impairment by looking at the iurnmlltion o fhel ring I<IMacross a range offrequcnciuralbcrthaniltsinglc frcquencies

.. ..tr y RollinlOn. a iJarri.,e r;ronl v niwr,ityChambcBinSydncyand alcading l dvocateofhearil\i 10.. cllimants • •po!<e on !egi.l l'live dr<elopmen tl and legll processes. Hcnlmincd L'Iediffcrence> bW<ftn 'Norkcn 'Compensa tion and Common Law claim,with the li tter requiring proofofemploycrlIeglilenu. He ind,ca ted thlt cla ims fOfbearina loss rompensa.tion under CommonLaw CIUI be up to lCII times tboo.e under

Acous tICS Austr a lia

WOrU l"$' rompc nsation. He . 150 indiC.tedthat whil't the majority ofcl l im• • re madeunckr Worltera' Compen..tion I.gi slationthere illtrendlOWal'd.<Cornmon Law cl~mI

which can tlIke signifICantly k>naer timethroupthecoutUbulwhicbtohifl<now l­edge ha\'C bem won io 99% of cut$. MeRobil\lOll\presentatiOll onthenilM watcolowful.nd provo/<I;(I . Itronl responsefrom """,e membcn of the audience dllrinlqueOllOlltlmc:

Lou l. Ch . lIl' , of acoustic. l com ulling fi rmCh. lli, <It Assoc:i. tes and member of theSta ndard. Committee AV/l . .pokeprincipI l\yon Au!tralillJlStandal'lb AS 1269Ind AS 1270 cllrrenlly under m'iew withdrafl. rnoision.to bc relcl stdin eith. rl.t.1993 or in 1996. He .po kc "fthe ".ri o,,"aro~p. rcprC5(:ntrd on the relevant StandardsCommittee. , OCIUe of the baie . formina theStandards discussed and ofnoist Icvel andnoise doSlgeli miU

Dl\id Ed. a , Ofa.:ouslical consulting firmEden Dyn.un ic. (soon 10 N Aco~ .. ieDynamic a) and member of Standard .Comminee AV/l. "poke 011engineering.ndadmin ittrariveapproac:heltooccupation. lIIOiK n posure reduction andeontrol dis­c,,", inll.in particular the difference,bct_laboratOlY Ind work place perform ance ofhUri ng prolrctlm, Davidalso introduced hi."OVClcot>eept of"larraling sYJlem(~pro 5

ltlt l ) for rl ting employerorga ni. ation. , interm. oftheir occupationalnoist e"" iron.mcn!. Thi, WO\Ild be bast don occ~pational

noist u pOJute level. and effectiveneu ofadminilt raliw and engineering noist <:ontrolP'''i'''lDI. O....idindi l;l.!edthat hcwould lik.10 see more funds directed toeontrollingnoi.., .titl SOlrrCC rather than althehcarinabs . ompenSltion industty end

f ollowing tile meet inltth e majority ofthOJcin .llCndartec adjoumedlOthe in house cafefor food, dri .... and discUS5ion,conc:ludingyet lUIother . uc. eu ful IUId stimu l.ti ngmeennl

Capitol Theatr eOn Monday '1 October the NSW Divisionheld itl AGM in the Dres. Circle of therecently re. lnred Capitol Thea tre in Sydncy'sH. yml rl<et. perhaps the: grande.t I nd mOJtorna te sctl i"1l fOl an ACO~Slicll SocietyAGM to dale7 Immedi. tely following theAGM atechnio;a1m ectinll.wa.prescnll;(lonthe uc hltcctural and m«hlnio:al strv ic:..ICOUllics work that wcnl into thc reSlOnluOIlThe .n endanc:e wa• ....,und70. ofwtJi.happroKimalcly a third~ from ardliteetura1

r_h lerK_ land. of ac""'tical . onsultingfi rm Peter R. Knowland and Associ. .. s PlyLtd ....t1incd hi. firm" role, onbch.alfof

Sydncy Counci l. in prep arinll the briefsm ing the acoustic pcrformlflCeparamclenfOl the theatn: re""'ra tionprojea. "" ter . lsog...... I brief hiSfory of how the projccl hadcome . bou t. inditaling that conservat ionardl il«ti Lawn:1'K:C Nield dr Pan nen hadsUliestcd the re. torallon of the Cl p' lOlThea1rein.n ideas compctitioo Iooltioa It analtemaliw venue fOf the AUi1r1llian Opllnlwhio;h al$O coinc ided with pressure . l lhetime for I new lyric theatre hiving . 2000seat ta pacity for op era and billetpIlrforml n"Ct'. It w.. cmph. sised thlt thetheatre\original acou. ticalcMracteriSlic.were ro be prest rw d including lhe soft formceilinll,difTusionldjacent tothe.tage,Icouslic vol ~me and I full occupanc yre\'ctbe ralion time of aro~nd 1.6 secondsAmbient noise lcvd goal . o f SR18 andNIUS-...:rereopect iw ly set for the.lldJellCCIlid.tage areas. 1lIc: winning proposa l wa.pnwidedbyfleteM r Constructions

S arry roturr l)' of lCOllStio:al COllsultinl fi rmWilkinson MlImIYP'tyLtd thm spol<e ""thereturn l cou stical desig n brief .nd IheinI'olwm ent bi. company prO'l'ided in 1Mrelli lllltiono f the refwb isiunent works. Barrycommenced with • descri ption of ias~..providlnll.initi.ldrsignconstraintsin<:luding(jr.rating.extcn.ion in.tageSluforopcraim:luding lraist d fiyt O"'er.operabie ceilin&hltche,fof light proj«lion.insoal1alionof lfollow spot room abo". the Dre.. Cirele, .ndprovi.i on of multipie use rooms back ofIlouocad jacmt to the main thcatre space

Whll" IC«T' ting most 'Of thc mitial tenderdcaipbriefthe Ollly .igniflCanldcpartllrewu ill relll iOlll o control of 1r1linnoisc-1lIc:estima ted Co.l to reduce the inilial :-;R5GtrIIin noiM level. in the thealn by trackisoll liOll\\>Ollldhavebc m $U m: So in. t•• dilwa sdec idcdworlronlhe th••m-e ilsclf witha . omb,natio n of smrcnua l isolatioo .ndprincipaUy constru<:lion ofthc:rai'cdstaae. nd ludience n oors and low frequ encyenerg y absorb e.. , Although initil ilyquestioned the NR18 dc. ign criterion wasfina lly ldr>pll;(l,Ba rry indlcaled lhat there arwall of the StIli , was bro~ght forward 10impr"""acoUltics in lliis ..el of the theltreand ro l lll1Wan incrca ..,;n foyer silC. lnorder 10 m.inl ain me el isting inlem ald«oratiw f..~••ircooditiooing oullets"",re c"""".led above the nl ge pros<:cniumI rch andabO'l'c the bK kof th. thcarrc . and<hehowe sound ')'I tem concull;(lbehind thedecoralions each.idc of the'lIge. Acou.-tical.bsorpI'OII was placed undcr the ceiling o fthe fiy tower to con trol m-erberalio n af>dabove the olChcltrapil to reduce ceil ingreficction. 1lIc:carpet ed fioor in the l udi. nce

Vol. 23 (1995) No, 3 · 109

area was found to have little effect on spacereverberation times.

Much attention was paid to improving theacoustical performance of the building shellwith up to 3 skins of brick being used insome places, such as on part of the fly tower,and construction ofa new roof I-3m abovethe existing roof. Undermost rain conditionstheroofmeetsNRI8,however, under heavyrain it meets NR25. Barry also explained theinnovative approach employed by the Sydneyfirm Optimus in the provision of airconditioning airflows and noise control toachieveNRI8 within the spatial constraintsimposed. This was achieved by locating theair conditioning plant room in a buildingadjacent to the theatre, use of perforatedplate on the fan discharge (pointing awayfrom the theatre) to reduce air turbulence andachieve a more uniform air velocity profile,acoustical attenuatorsprincipallyinthe formof internally lined duct at the plant room andtheatre ends, and circular duct work whichallowed air velocities of up to 7 m1sprior todistribution into the theatre space.

Both Peter and Barry spoke eloquently andinformatively with the meeting being very

;:~;o:~~~V~d c~~s~~eof ~:se t~ att:~:~~~approximately a third of the audienceadjourned to the nearby Roma Cafe for apleasant lunch and to catch up on the latestgossip.

ACT MEETINGHuman VibrationOn 24 October, around 40 attended a jointmeeting of the ACT Group and theMechanical Branch of the Institution ofEngineers to hear Dr Hugh Williamsondiscuss various aspects of vibrations andpeople. After explaining the good and badeffects of vibrations he compared the Britishand the ISO limiting criteria for exposure tovibration. The techniques for measurements,which incorporate transducers but need tominimise any effect on the activity of theperson, were discussed. Hugh then outlinedsome of the projects including a study ofvarious bus driver seats which were to beused in the new local bus fleet. There wassome mirth at the thought of' a hefty busdriver sitting on a seat pads with embeddedaccelerometer. The problems of suchinvestigations in adverse environments, suchas mines was also discussed. The meetingwas well received with much discussion andhighlighted the benefits of such jointmeetings.

MarionBurgess

110- Vol. 23(1995) No.3

VIC MEETINGAMRL LaboratoriesThe Division's AGM followed a visit onSeptember 20 to the Department ofDefence's Aeronautical and MaritimeResearch Laboratories at Fisherman's Bend,which 23 members attended. The twolaboratories opened to the AAS visit wereconcerned with Human Factors Technology,and Vibration Analysis. Variousinvestigations in progress were demonstratedby aural or visual displays.

In Human Factors Technology, the demon­strationscomprised:

i) a binaural technique (using the Aachensystem)of3-dimensionalaudiorecordingtosimulate the noise ofa moving aircraft heardfrom a fixed location, to enable its directionand height to be identified. The recordingtechnique used a standardised artificial head.Recorded examples were given of ahelicopter moving overhead from right toleft,andofuptofoursimultaneousvoices,each in a different direction.

ii) the conversion of radar outputs of threatsto an aircraft (eg AA activity, and gunlocation) into coded audio signals for easyrecognition and identification.

iii) the development of hearing protection foraircraft crews through noise surveys using anartificial head, filters to simulate humanauditory responses, measurement of third­octave and narrow-band sound levels, andvarious types of noise reduction using a hel­met with ear muffs (SLC80 = 18 dB), earplugs added (unsatisfactory forcommunica­tion),andactive noise reduction usingreversed phase noise.

iv)thedevelopmentofaflightsimulatortoachieve perceptual rather than physicalfidelity in the reception and identification ofboth visual and non-visual cues. Auditorycues from aerodynamic sources, engine,hydraulic system, runway and weather arerecorded for noise location purposes,together with vibration monitoring at thecrew's seats, etc.

Demonstrations in Vibration Analysisincluded the collection of vibrationsignatures for the purpose of conditionmonitoring of engine and other critical parts,and the detection of cracks and flaws. Thedetection of cracks and flaws is the moredifficult task,but is aided by the testing ofcomponents with deliberately-introducedflaws. Both laboratory and field tests aremade using up to 5 accelerometerssimultaneously. With regular monitoring,many flaws can be detected up to lOhoursbefore likely failure time. Recording is

generallydigital,andcomparisons are madein the frequency domain using signalaveraging techniques for greater clarity.

All members anending the visit agreed that itwas a most interesting and informativeafternoon.

Louis Fouvy

NATIONAL VOICE CENTREA National Voice dedicated toexcellence in the art, and care ofvoice, has just been from thefaculties of Health Medicine,Engineering and the Conservatorium ofMusic within The University of Sydney aswell as the Royal Prince Alfred Hospital andthe Australian Opera Auditions Committee.The voice clinic will offer a world classstandard of medical care informed by a multidisciplinary team of doctors, artists andscientists. Knowledge about voice will betranslated via regular workshops to healthworkers and voice teachers as well asprofessional voice users including singers,actors,teachers,businesspeopleandthegeneral public. Australian voice researchwill enhance voice training and medical

Fundamental to the concept of the centre ismulti-disciplinary medical care, research,voice training, education and theestablishment of strong Jinks between thevarious disciplines related to voice inAustralia. Clinical care and voice traininginitiatives of the Centre, including teacher­in-residence programs, will acknowledge theeclectic nature of voice. It will be routine fora professional voice user to consult a teamconsisting ofa voice or singing teacher,doctor, speech pathologist and voicescientist. Research will be the foundation ofmuch of the Centre's activities. Up to dateknowledge and technology can offervaluable insights into the teaching of voiceand may reduce the amount of training ortherapy time needed. Doctors can work withspeech pathologists, voice teachers andscientists to provide a more comprehensiveconsultative approach to patients with voiceproblems and to professional voice userswho seek advice about optimal vocalperformance. This team approach model iswell established in centres of excellence

The Centre will offer on-going up-grading ofthe skills of voice and singing teachers,speech pathologists and doctors viaworkshop and seminar programs and afundamental concept will be to take theclinical and scientific voice knowledge out

Acoustics Australia

into the community via regular workshops,seminars, training programs and conferenceson voice to professional voice users, teachers,businesspeople and the general public.

Further information: Dr Pamela Davis, Tel:02646-6600, Fax: 02 646 6390, emailvoice@cchs.su.edu.au

SABINE AWARDProfessor Harold Marshall has been select­edto receive the Wallace Clement SabineAward by the Acoustical Society of America.The Sabine Award is presented, on rare occa­sions, "to an individual of any nationalitywho has furthered the knowledge of architee­rural acoustics, as evidenced by contributionsto professional journals and periodicals or byother accomplishments in the filed of archi­tectural acoustics". ProfessorMarshall'scita­tionnoteshiscontributions to the field ofarchitectural acoustics, particularly for theunderstanding and design of concert halls. Inreceiving the award, Professor Marshall joinsa distinguished group of previous recipientsincluding Leo Beranek (1961) and LotherCremer (l974). The official presentationtook place at the November meeting of theAcoustical Society of America.

ProfessorMarshallwasafoundingpartnerofthe acoustical consulting practice of CarrMarshall Day Associates Pty Ltd and is theDirector of the Acoustics Institute of theUniversity of Auckland.

AWARD FOR ELECOUSTICSElecoustics Pty Ltd of Sydney has recentlywon an Achievement Award from the AudioEngineering Society for the design of thesound reinforcement system in Courtroom 2ofthe High Court of Australia. Difficulties tobe overcome in the design included areverberant courtroom, widely-dispersedseating areas, speakers some distance frommicrophones, several microphones opensimultaneously, strict architecturalrequirements in relation to the furnishingsand fittings in the courtroom, and time andbudgetary restraints. Elecoustics received asimilar award in 1993 for the design of thesound systems in the House ofRepresentatives and Senate in the AustralianParliament House. The company has alsowon loudspeaker design awards

FEEDBACKThe review of the Basic Music IndustrySkills, produced by Ausmusic (AcousticsAustvol 22, no 3,plO2 included a commentregarding a lack of emphasis on reducingvolume to reduce noise exposure. It has beeninteresting to note that the latest editions ofthis package have included more emphasison the benefits of this simple measure.

Acoustics Australia

INTERNET NEWSAustralian Academy of Science

The Academy of Science has opened awindow to the world through a WorldWide Web site on the internet:http://www.asap.unimelb.edu.au/aas/aasbome.htm

This site includes information on the Councilof the Academy, committees, publications,and various other activities including thegrants, awards and fellowship schemes. Onespecial feature is a virtual bike ride aroundsites of scientific interest in Canberra.

Acoustics on InternetAn article in a recent issue of Noise &Vibration Worldwide, published by theInstituteofPhysicsintheUK,listssomeofthe various web sites that includeinformation on noise and vibration. Thesesites are also detailed on the web page for thejournal which would form a good startingpoint for any "surfers":http://www.loppublishlng.com:80/mags/nvIlndex.htmI

LOW FREQUENCY NOISEThe American Society of Heating,Refrigeration and Airconditioning Engineers(ASHRAE) has awarded a research contractto a team from Vipac, led by Dr NormBroner, to investigate the impact of low fre­quency HVAC noise on occupants of rooms,offices andauditoria. Current building trendshave resulted in an increase in the numberand severity oflow frequency noise problemsat frequencies 250 Hz and below. Howeververy little work has directly addressed thequestion of how people react to indoor noisein situations where the background sound isestablished by the noise level of operatingHVAC systems. The research objectives areto generate a practical philosophy and proce­dures for the evaluation oftheaeceptabilityof low frequency HVAC sound and to pro­vide the critical basis for development of lowfrequency design criteria for future publica­tion in ASHRAE handbooks.

Further information: Dr Broner, Vipac, Tel0396479700,Fax0396464370.

JOURNALS MERGETwo European Journal on general acoustics,ACTA ACUSTICA and ACUSTICA willjoin forces effective January 1996. The 3,000s16scriberswillthenreceivetheunitedjour­nal with about 200 printed pagcs bi-monthly,The united journal will be edited by the sameteam of associate editors which now serveACTA ACUSTICA.

EXCHANGE JOURNALSA number of exchange arrangements havebeen established between AcousticsAustralia and other Journals from around theworld. The Library at the Australian DefenceForce Academy has agreed to hold andeataloguetheseissueonbehalfoftheAustralian Acoustical Society. Access toissues or particular articles can be obtainedby normal inter-library loan arrangements.The journals which are reeeived include:

Acoustics Bulletin, Acta Aeustica, AppliedAcoustics, Aust Journal Audiology, ChineseJournal of Acoustics, Canadian Acoustics,Catgut Acoustical Society Journal, JournalAust Assoc Musical Instrument Makers,New Zealand Acoustics, Noise NewsInternational, Noise and VibrationWorldwide

INTERNOISE 96This 25th anniversary conference will beheld in Liverpool, UK from 30 July toAugust 2. The theme is "Noise-theNext25Years" and every aspect of the legislative andtechnical assessment and control of noise lieswithin the purview of the conference.

For further information from Institute ofAcoustics, Holwell St, St Albans ALl lEU,Tel+441727848195,Fax+441727850553.emailAcoustics@c1usl.ulcc.ac.uk

Peter Karantonis has recently left Eden

~:o:~~~~~ a~;rvi~~~ti~~te:on:u~~~~s :: h:~now joined Renzo Tonin & Associates PtyLtd where he is head of their Environmentaland Industrial Acoustics Group.

Rumour has it that a well known firm ofacoustical engineers and scientists recentlyhad an unfortunate incident with one of theirnoise data loggers in the early stage ofa roadconstruction projeet in the southern part ofAustralia. Local residents, unaware of thenoise monitoring takingplaee, were alarmedby the strange ticking device in their midst.So they called the poliee who in turn calledthe bomb squad. Unsure of what the devicewas they took a precautionary approach andexploded it!

Ken Scannell has recently joined Sydneyacoustical consulting firm Wilkinson MurrayPty Ltd after leaving the Industrial Noise andVibration Centre in Slough in the UK. Kenhas been involved in acousties since 1976and has had over 10 papers published onvarious noise and vibration topics. Ken islooking forward to a bright and sunny futurein Australia.

Vol. 23 (1995) No.3- 111

STANDARDS REPORTThe following draft standards were issued forpublic comment by 30 November 1995:

DR 95366 Description and measurementof environmental noise-Part I: GeneralProcedures (Revision of AS 1055.1-1989and revision, in part, ofNZS 6801:1991 andNZS6802:1991).

DR 95367 Description and measurementof environmental noise-Part 2: Application tospecific situations (Revision of AS 1055.2­1989 and revision, in part, ofNZS 6801:1991andNZS6802:1991).

DR 95368 Description and measurementof environmental noise-Part 3: Acquisition ofdata pertinent to land use (Revision of AS1055.3-1989 and revision, in part, ofNZS6801:1991 andNZS6802:1991).

These Public Comment Drafts are theproposed replacements for the currentAustralian Standards dealing with thedescription and measurement ofenvironmental noise (AS 1055-1989) and theequivalent New Zealand Standards, NZS6801-1991: Measurementofsound,andNZS6802-1991: Assessment of environmental

Standards Australia will also soon bepublishing ~ revised version of AS Z41-

1969: Octave, half octave and one-thirdoctave bandpass filters intended for theanalysis of sound and vibrations. Thisrevision will be a reproduction oflEC 1260­1995: Electroacoustics- Octave-band andfractional-octave-bandfilters.

Grant Cooper

Housing Code Standards Australia hasrecently commissioned CSIRO to preparethe initial draft ofa performance-basedhousing code. Committee BDl78-DomesticConstruction believes that a performance.based code directed at the specific needs ofhouse construction, is long overdue.

CSIRO, in conjunction with a specialist sub­committee of BDI78, will prepare an initialdraft for the committees consideration. Thedraft will detail performance criteria for boththe structural elements of the house, eg. roof,floor, walls etc, and fire resistance, togetherwith utility items such as ventilation,dampness,sound,energyefficiency.

It will specifymethodstoverify,eitherbycomputation or testing, that the requiredperformance criteria have been satisfied.The committee is particularly interested infinding out if the wind and live loadingrequirements currently applied to allbuildings are appropriate when applied tohouses.

ANSI StandardsNew American National Standards areavailable as follows:

ANSIS1.26-1995 Method for calculationof the absorption of sound by theatmosphere. ASA Catalogue No. 113-1995.$US80.00 per copy.

ANSIS3.7-1995 Method for couplercalibration of earphones. ASA CatalogueNo.112-1995.$US80.00percopy.

ANSIS3.20-1995 B i 0 a c 0 u s tic a ITerminology. ASA Catalogue No. 114-1995.$US94.00percopy.

ANSISI2.2-1995 Criteria for evaluatingroom noise. ASA Catalogue No. 115-1995.$USn.OOpercopy.

ANSI SI2.42-1995 Microphone-in-real-earand acoustic test fixture methods for themeasurement of insertion loss ofcircum aural hearing protection devices.ASA Catalogue No. 116-1995. $US64.00per copy.

Standards published by the AcousticalSociety of America (ASA) are available from:Acoustical Society of America, Standards andPublishing Fulfilment Center, POBox 1020,Sewickley, PA 15143-9998, USA. Tel +1412741 1979. Fax +1 412741 0609

AUSTRALIAN ACOUSTICAL SOCIETY1996CONFERENCE

November13·15

Making ends meet.UInnovation and legislation.

For details please contact:Ross Palmer

Telep-hone: (On3806 7522Facsimile: (On3806 7999

Note: Call lorpapersalfached inthis joumalasalooselealinsert

112 - Vol. 23 (1995) NO.3

NATIONAL ACOUSTICLABORATORIES~ ACOUSTIC & NOISE~ SPECIALISTS

Superb Anechoic andReverberantTeslFacililiesServicing:

o Transmission, Sound Power and Absorption testing

o General Acoustic Testing

o Comprehensive Analysis of Sound and Vibration

o Measurement and Control of Occupational Noise

o Electro-Acoustic Calibration 0 Vibration Analysis

Experlsin NoiseManagemenlandcther servlees- Including:

o Measurement and Control of Occupational Noise

o Reference and Monitoring Audiometry

o Residential and Environmental Noise

o Education and Training 0 Acoustic Research

126 Grcville Street, Chatswood, N.S.W. 2067Ph: (02) 412-6800

National Acoustic Laboratories is a Division ofAustralian Hearing Services a

Commonwealth Government Authority

t~... 1BRUEL & KJAERNoise Mooitorin g Stati onThe 337IL..mvn.m-talnoiw monitorinloralion com prise, the 2236 SLM and Iruharlablc NneI)' ill. "'Uthcrproo f•ponabk_ ....lh lO<al ~ishl only 1kl· A

DAT """"*' can be inch>dni for rvcmR C<)rdinll·

~Insurlng AmplifierThe 152S mcnllrinl amplifler; I' co mpulefcontrollN lc~l lIlOIl i lOl withllattTllnd ..fcUpo""" NIId;onl ideal ly 1U,lccl lO.U.....ual Of aU_le d Il\CIS~Cfll

applic.llions. II ~ ' hall P=i sion.1_ noiu: .l illlllr rtwlnc.l mnsurin, amrh fi... ....jlll-.d~lnlfealUlCandlllCTMl

\IMal_ iooonfacc.

Evtde eee Se rtwe re~£videoo:clOtt.~ 1)~7696i1 .t<1 of

IqlUI1lr.. ...,~IDOls ... ~lIsa1onlMmeuut'm'ICfIlcbladoovnlNdedl'mm1l>e2260SU 04.ll eRlblcllhe llHrlGprod \&CCIMln LlI, M reports from IlOIUId~ptlIc'mIin the(lCldorll>e

lahom ory and .lllO\1l'Scu Y opcl1ltion wilhothrrwindowl b.. ed IOftware packages forVIOI'd procruinll o"p<eldo hcctl

QC Bra inSoftw""' WT 9550, or QC BIlIin, is • •mart1Ol1lrion1O'lua!ity«M>lfOl ~sti"l~on

tMsameprillcipln.iMbumanbn.i1l.~lO~canm:otP'lOCdJf!"crencclllI."""w

and yitnnon sll","l_ !hI.t IR othcroiiwlIIIdNctMllelOlOlcr","boPcd lOltwruc

• TMIOIennce ....~...uc.. bcJUlUIlCd,dioplayDJlndedllC'dll"d1yand....,.F...-.-~. BrwI d Xi-r ......(P01IoI 1 11 T~HJb,""SIII'1f)MTd (fJl)

4SOlO66. F.u(Q1J 4J01J1'1

ACOUSTE XThr IOIlIld lbIorption properue~ oflf"W)' onA<OUlla <"n l » i51 in l <hin inil ihe quielinl;male l lmooph. ",which i. ofl.n w u¥hlbyon:hileclJlnd in"' rior designcn . The matcri ·al ..... be~lOmateh any cnlour scheme

Ind IJhe "'l lO a ll surfl ccs. lIc,,","inl""Ofinish ..' slll'odard and an:hiloclural. Whe re\he~ rUliiohi, _ pnc lical. A ..M . _ hul wick .....,o of patld .. t-m...I nd other poodlKts.

F/ltTfIwr- ...p-n-: .4......"'" P/L II DiJIJ1.Sr. cw~rIC J/ 1I1 Tft(OJ) IIS96S6ild

Fu (OJ) IIS911J611

CHAR'1.4.C I:"iDUSTRI ESCornprdwnaMdata on 1M Doioc errllllOdflOOlsil typaofsoll pipes elU1'mtly IOIC<l inrr.uItIslOl'Oy~ ia_""IabIe.Thr

l...u ....re~wiollCdb)o~

1~ and cCll'llklcted .. 1tIcSltlOlWAc_ie, LaboralOfY USinl I !Cst wall

insIaIled~Ihor_1uJe~

~Thalb&la1\owsfor"dlc:ODmpIn_ol

thepmonnanccofl1lerbfftrcmp'l"'mawri·111 r:umntly used in ee ...niury p1wnb inll.,­F"" M- ir!fon-'lOII:nanrlllC' /lIdw_ •.POH M } l Mi lpmu, NSW11/4 T. I (01) 7141/44 Fo r (01) 77/ 4HJ

MICROTECII GEFELLPtsecn phcneMimlcec:b Ger.nhu '*-d Ihor..... SOIlIPis~. I .-11mallU- indepe11cklllIOIlIld .owet foI pm:isc a libntiO'l of IOWIdleve l mc1Crs and com Flet. KousIieal_ .... nn ll sd.. The pi1lOftpborw it1IIpJlIocdin.qllll ilY......:deIl ..... .....>dl. lso inc h.c1... toarom.'crwilll lpeclalocaimloa..toidllllclOW>dieYel~

~C.llllbe.-ldirutty.Opnatioal iobyl

ne.r · sile o. ric rnO\Ol' "' Illch mO\'Ol '­pistons in . preu un: chambnlO ...hich lhrmicrop/lonc bein, cl libnled it.nachcd. T'1lr", AOII ~ aenrra les . aIeIlly -"lc

l iI\UloOidlllh crl1llinll Pf"lure"llOWIdp", ..u'" levd of 124 dB. The pis1OIIphone. 11".,., USCBloo;a~br.le microphones wilhcaptUl. <IilllllderJ of l illCh. ll2 inch andl 14iroch. Correcl iOfl f.Clon can be u k.n inlOilCCOlInl for micfOllhonu of c1iff.,. n. volwnc

FtutIw. ,~,.... · s"" ,ilbGrol T""' ,,,,, PO&u66J7,M~/'-"..."I1cJ()(J(). TdOJllMl4tuJ}.FlUflJwtrHtu4P.

" IPAC\ 1bra tion Tran sducersI. Mooilna W has added. llC"'tmn of0l0dria 10 tbcir rulJC ofLVDT dioplaoanmIlrIMdllCel'l., "" .11 minllll1nocd illl.,,,1elCClTO.llclpn>Vidlnll. 4.2QonAootpulforUK in pcocfll cO>l1101 IoopI Standard........nnl ",nl" an: ..... ,l. bl. fro1\'I . /.2~mmlO "/.6OOmrn.forrbl'fcrinlilldulU111

.p pliclli on., ~.riC WI consll\lcl ion ' lylu .reavaill bl• . t he heavy indu'ln ll .rU8Iled bou.inll comp let. w,l h Inl.llr .1mc>WIlin, bcarinl'. 1m1<lUn:c1 .:abhn, and IWlIl. rp roof O91i0ll , A pR Uuri$Od $Oriel hOIbe.nd.lll"cdlowithsland .p....wrelIfIdi.... of 6000 poi ...... thclrlClidlKa'

""'"2. MQllilnft \ ..... 1100 MfICSlttelmJcncscn lII\ e t>ecn de1.i. Md rooyib..llo......lS>IICII\Cn. ill the lOCI,,,

.......... condil iomoftemptr&l\l.R.UJ>1O2 :lO(C IDd~ .... i""""10 10"10ra<l.RdlusIIy.onstrIICIedinsllinlnl.-J.tbc pcczoc loctnc; l!Im«....~1llaSCIl'tITIOlranca"P lOllQawi&b.frcqoocrqraponocfronc 2 10 1000 Hz ....:I • 1nnSYCIX

lCIUi. iYily of S'I. . T'1lr compactaecdtfolllC1Cn .... lgII .pprOltimal.ly 100,..-and_offCftdwilll.cboCcofCllOUflIinclt)ie!. .... h.idlllllMado,sn.dl1IIdmajpltUc fininp

) . Molli tnn leu "' I d • '."110 o findUSlrial ocnt ors t1icl . wi\l morillo,posilion, di sp l. ce mc lll. -.n.n., ndill~ibllllion and sp".d .. n hout ICtll.ll <ont. ct"' illl thc mO'<inll lal"g., under inves lip lionThe MIN probn ha~ I . implc CllIlW1.ICtionCOMiSling of. pon ed eoil IISmI bly whichradi.' •• a hia h frequcney signaJ inlO l!lecond\lC.iv c WICI. Eddy currenll an:pcodueed ...tlic ll can be rnorIiWlrCd • • de~lreprcocn1in,the"'licpp. or ....k>d for 1M ck le ,rn i"" . ion of ~&ryIn,

proflkt ill dynamie '*""c Sft'CfallllOdd.... ...'IilabOewith""""""11 ""'JO of 2, S&lid '.S m m and • cho ... of moucJ:' ''Ieonfiprationt On.ia* foI meaowerncncotamallrbSUlncn.rhepn>bca .... abo> !le.... w __ apcedbymocutonn 'chc

peowp: of. bole will"n IlIc drM lhall....mbly. Th . ","suri.. , .~.m i.eomp l.~c1 with . Mon,tnll probe: 4ri\ocrnKl<lultwhich operales r......, I de wpply andl"""idt s probc adjus tmC:nl and ca libraliooconlro ll and ln oulpul for dna co llc<lionsySl. ms

:"ioisebad ge Controllert • ..., n Davit ......lnocdIIw Mode I 70SkC .I hand held .~iee tlw penn i\l remoccconIIrol ope..llOll of the to Mode l 70'N.....lloIdBc A I ocr c.. lCIiYOle1hc Mode l70~ willlOCJI I cOlClpUlcr by $Onc!inllCOCNnI!>dI froon.... 1OS1tC ria \he salIIiccIaflR .~ 10 "" 1'OS. lbc ?m ltCclllrun.1Ulp, cal,tnteand ..wclllcltl ' T'1lr10j kC is ideal tot "'YB who "'iah 10 ICIM\he70SMoatbospot _intlll:r.. ld"' .. thulhanprcprOJramminl1hc""""-P timc ariddala.wilh I compul.r and ~ soft"'lR. The:c1ilT\CllliOllll Oflhc~RC "'OIIly'2' "

' .711 1.91 em •• nd n .... I&!>II IJ . complcl•"'1hits l.'vollAAAaluhn.banelY.

Signa l Cond ition er

La.- [)a "; s hu recently rel.ased lh. "''ode l22~ Mi<rophon. IAccol. rome' . ' Silln.lCondiliooi nll t.lod~le. The Model 2204 it.Ilp>ed f... ..... ""lh • ,ange of TEACcom;llldDATdaurecordtn.fac:iliu till,thc:use of . ir-eonOtllKr miccopho ... . andaocelcroc'ncttB utnnsducen. Them;Ofderandlhc si,...lcOftdilion i",tr1OdI.J.an:iDItl med inco a sm,le pKUse WIth .U

'otll. 23 (1995) No. 3 · 113

I. INDEXIr Volume 23, 1995

A.A RTICLESBIES D." ., So_ "'OI~I on SabineR-....,f1/o. J. ' , · I OJ

CLA RK N.C.. t.- F~ AtN.oh.t

Cahbmion of A«ckromrl~ No. 1.

'94'nELD Co.FRI CKE r .. OplImiNli.. ofBIlildi"ll Val til&tKla Opcllil\&Sift ill I:-;oisy~No/. S-l

f RJCKE f .. HOO~ HA~ C..Pmtic1io. 1M ACOUllia of CooocmHal.. U5ift'Ill"",ncal NNlal~

N4 J, S1."

HOWAR D I.. V,hr. ,LOa 5' ....1

I'noc:aaina Usina Mad 8b,A 'o l .'-l J

HQW4RD I.. NoQc aJ>dVimr- DMo

~"'"16bolPC s.-de.",s. Hol. •}'"

MIKI K.. Ord'ntn Music: An

~o'Ilisk."·o 1. JI·"

MlJRRA¥ B.. Nocu 011 Off_Ac:ousriD,No. J. IO~J0 7

JUNDtL U L, COIIlP"ter Sun" LM_Tedlniq lln rOlf Aeoull,eal ' Jon i,.. ofR........, No. J. ' /-IJd

" 'AU ;H D.. R«e lll ~tloplncnu iflAllIua li&JIOocupatioAlJ Noioc Poiie)',NoJ,lMfJ

ZH U S.. M r K Efl.ROW J.. Simulation of

.RtppleTank,No l .J1-6J

B.NOTES

BALDWl!\; K .. C RO!tI PT O N R.. Blck

OIllhe FASTS Track,No l ./U-IlJ

BENBOW R.T.. Wind (i ..... ral. d To....lNoi..,. A Proel;. , 1Solution, N~ 1, Nl

DO N C., Aeoul li. , inltl the 2hlCtnNry.Nn!. l ! ·l1

WOln: J ., A S)' l l. m For Rt l t TimrMru urement of Acnu.t;c Trl n. (e,FlIJl(;lionl , NQI , J9-10

c. INTERVIEWDI::Sl'iIS G l flBINGS, Anitl Lawr~nc:~,

No /. ]J-14

C..", ../atlvrb"Jujor Hl/.......ts JJ·UIlJtnJ III1l(J)19·JI

'''' - ''''01 23 (1995) No. 3

~1"tri",,1 coMeC'lioN intnnal. f ow andfl&Ill input dwmcl veniM l are avail. b1e,'IIlfith inputl)fltl indj_idually Klecttd by~hannd. The minopbonc inputl aR60iped fOI" IlK willi LV~_

micropftonn UHl LD mi~

prnmpllfoen, Dependln' OIl lbe lllCldoel of• p.eampllfler, u la\l.ion ...,bIe ImP. of up

"'UOmctm .. poIIlbIe, Tbedo~

of th~ comt.iMd reconkr and l ipalCOlldilicwli",lInit l:C l50lt)()6ltlSOllU1lWldl'IOI&1~iptofl. II K.

Computer-based Traini ngPro&rams

I . MEDIACOUSTIC if. . _hins"'ttwarop"'kqeforloCO\l.Slln The piCUa clibucilOIl . CCllUaICOftallllislin& offowm.ai........,.:PbyWofSoo&nd;$INnd...t Man;~...s BWdiap; II>dSoixe-uLbdmooM:iliU...-cdby..-ddip..tat. pictwn,...s ridaI ............. 1M....... 1)'Wtllcu bo-'led lil:l: • •dcr·_bool..MEDIACOl.,;S11C iI~ ..l CD-ROM.conrainir'C lIf'OIIIldJOO 1018 of...2 .~ hurduM:da IflinlqCO

- lftll'OCl:>ction III Madomc Vlbra_ - . 1M

I)'IIcm nIIlJ 011 31-61" &6 Pel willi MSW1lldt>wl3,I, Cl). ROM reackr and ' MBkAM . lIIcn PfOC"Cl' e lhcir_ .. ~1Ildkeeplnd nf lhcir praeraoYil .....somty.~ncr.ud mulliplc clooic~ 1CSl1. Top ;",indudc vibrali"" l'undam.eMaIl, theory of~r..c n>airI_ . h IM VI hqumcy4111 p~omlltioa, ffT ....iylis anddia~of~rK"fllllJ.. i.lNclIil\Cl..

f .,.",." /k1aiJ" Ms fblll SltHlwn. VIPACEII, ltffft'l,..tJSClAIUfJ lld,11JNonroa'lhyRJ.fb,tM.tIt>ownl<!. VICJ101. T.tI OJPM19100, FiUOJP646 4J10.

COMPUTATIONALI\-n:CHA~ICS

DeasyCompuUluonal Mechaniol AU!llrl.llI; 1 hJ.I

releu edlnewlln,eof..,llware forSDlviol3D Il;Ow ticl l"" blenu . Known ' l 8 0undaryElem enl Analy. il SYl lem BEASY·Acoul ricl, thelollwuchl5 bccn de. igned tobc l ble todcll wirh moSI, if notall ..peenof indullri ll , ooustic prohletm includingInte rior. cxterior or combinedimerior/exterior ar\llly!lis, BEASY providespoint IIId line illUrCes along with vclocityI nd Impodanc~ condit io... of e e vibratingIlrucl unl surf acn for « cura te mode ldncr iprion. Aco ustic domli nl ItC

repn:Knttdby:roneI.Diffem llpropcn;eocan bc dc:r 'ncd for cach zone.llowing

allllylil o f mullil'lc ..,OIllli e "' I' OftI8 EASY pn:MdcscompreberWvcdil'lIOIticc'l"'bililicl.llowin,Ihc IlICf IOdc:lenninelbeoontrilMllionofcacbl<llll>d~lOlhe

IOIIndptnWle lrocl ll ..ypoint'Wilhinlll c........F~rl~ 111/0"",,1;-; C_pt<la1lONJ1Mrdliurk. A......ua..1Il, UIIlI II . 4-8 QIo­51 ' E.NTlEr WA610] . Tft (99) JJO~16.

FiU(f19) 4H/Uf

DU~N AIR COXDlTIO:\I :\ GNoise [ _tel'"TheNciIc UIa ICtlvc dl.oc'I"'lenccr1)'IICftI,whJdICllllIIolrlSlllled in_buildinpor1dde4 10 « ill in. Oucl&. includon IprvpnelIfylCllVClIOiicc.anccllitiOlll)'WtlliatqraIed"'" f'P'ivcIIlcnccf . The uniI.... becllokvclopedby~e-ct~T~ofIhcUSA_~by

.....'.. lhclOllftdflddlilhelqtnmrlJofdie silenc er, f llton", I!lII 4111 andCIUlp&lZIiac_iavcnodwniOlloflhclOllnd( 180 ~ OUI of plwcl from I1ouoiopeaku_Ihca.Jofthc ..... TboIIIli-eoiK 1ip.l1 cancel< the otreDdialIOIIfldIlld~of~lOl24Bbn-c

boaaKhlcval. I60lh

FIU1Mr j~OII DIo.... ..1'-"Cooodiboori",. PO h 11J. MO.'OA .:.tLENSF 1I 0J. T.(O]) 991~ 1199. FlU (91)t9191J 4j .

I~...COURSEAudio Engineeri ngTI>c GradUll e Dip lo:om l I nd Miller ofDOIia:nScie"Cc (Audi o) 111"1:bee" cfCltedtopre5Cnr a . tudy parh forthooe Imeruled insud,o pro fe..ion,topro..-;d!: I bro.od audioc<.!ucl lion, ~l\Ible contin lllnilelf educl t;onand 10 enoouu ge reoearch in audio. TheOr.d UlIe Diploml can be comp leted panlime In 2 yearl I nd lh~ M"I~r of DesignScionce part time in 3 yean or full lime in 2yearl , Also l ubjccll cl n be unde ru kenindividui lly.

Further infl'>nt\l1ron: DltVi4 Bartolo, DeptA1chite<;1Wl: lIIdo..lia:n Science, Univer>iryofSydnoy:-lSW2006,Tel(02)lj I2686. Fu(02) 3jl l 03 I Clll1II dads@ an:h.&\u du.au.

CONFERENCES andSEMINARS

1996,._ .,. I~II . SI!"C APOR£~MfttiJI.. SociclyofAc:ousotIDetai I-.; [)r W S(;an,eJo ACOIIStical~aPty Ltd, 10'l·2 121NKMtionCenIre.1'o'Tll. Nany&llJ Ave,S inJapo!t'226). RcpublicorSi~

Fall ~S 79I )66S.Td +fl' 79 1 ]2U

Fib ..... .,. n· ll. !>I EL80 URN[°AIlSlConil ""Applitd McchMliQ 96o.laill; AE Con- t nlion. (ACA M % ), POBOllE181, QuemVietori. Terne<:,Acr2600. Tel «6 ) 2706 S62, Fn (06)2 73 2918

Frbr,, "r y2 4-11, SVDNE¥• (k~upillionll i njury Symposiumo.llil. , OccliploliOl'll.l lnjury Se=wilt,Pll;>fnUonal Edu<;alionJ'nlsr;un,Nllioaal(),;c HeaI1llll'd Sd ety CammWion,GPO~'8,Sydnty.SSW200I .

Td (021S6S9319. Fu (02I S6S 9JQO

April 1"" "'TWERPForIlm ....IN*ticum96l a COIW. Eumpean Arouot in.AMOC.ONi":Fon.anAcustian, T« hnolo&icaIbnlilUlr KVN. Dnpinlci 21., 802011,~BcI,n.n.T" "'32 32160996.

r.... ..)232 16068'J

Apt't2,""U. M1Cll IGA..~

JoinI "-'II'Ij;OrClllUI~Socidy

an4 MidlipllVIOiinmaleri Auoc .Detail"e.t&ut~ticalSoc.Inc:~ 1 12

b on A~, Montclair. Nnr J01W)'07<M2.USA. Fu +l 201 744 9191

.' I ll)' "'-17 , IS DIANAP'OLIS1)1 01Mmins MotW Societyof AmentaDc1.ik; ASA. SOOSlWl)'.ideBI.ll~

Woodbury, NY 11797, L:SA. f.~ +1 516576 2317, em.oil dlirle@.a ip_0fi

l'tIay J.J..2S. MOSCO"....COUlliu I Me...unm .nt $o..t.il $:RuAj.nAcoU5'ic.ISoci~y.

4 Shvemik St. Moscow 117036Ruu i•. r.... 7 09S I26 841, •email bvp@uu ecc inunn,su

May n ·1". AL'TRANS4lhS9«<h~ Setn'NrDetalIa: ICP_IS!'G. 46....., f e li. VLalIel.38031GraoolHcedeaOI. fnDCt.fu"H76 S7 47 10. moail ell'lOspm@'cp,pnrt rr

11S . Vol. 23 (1995) No. :3

May 11-31. MOSCOWlnd S)'1IIpou.... on Al:OIlSIic RC'mOlCScmin.of tht A~and~

DetaiIl :SKmlIiat ISARS'96,.3P'yunkyLlIlII.M-. 109017RusaiLf... ..709S1}) 16Sl . crnail postmasln@;i.p tLlIIU ..

~b)' l&-)I . P ISA

S oiM lIII1"....". ·96 ' lnI1«W\fomoor OllAc>luIOU&JIllbedlllp!aMin1o.cc.;l.:Guido~ ril B~2,

201"" "',Imo, Italy. Td " 391 48011U3.F... ·)914lO11S39

J.lltl~1.O.BARI

1J1lIIIIIlConjms of AI'dioloiYDcll iII Au4ioloo andOtoI OJ)' CtnltC .Uni-.rtu lyo f Bari. 70124 B.n, IWy.F... . 3!18460224. cmail nam96@hul.fi

II/"tt7_11 . ~orr;JLorr;G

' '' lh Inti Symp011Nonlin_ AcowticsOt t., II: RonJIle W.i . NiJljingUni-.rra'Iy,!nstitUl,ofA COU$ticl. N. njing 210001.Ch,... , F.. ..862S 360 S5S7.•mail pmtndi@l\iu,educn

Jll ne 24-11. HERAKL IO orr;, CRET E3r1l l:llf'IIl"'anConfonlJndcrw.ttr~0IIIlie$

DcIl ,II : JS I'apdakis.Foundaiion forlleHarch aDdT«IInology.PO Box 1527,711 10. HtrakIion.Crc:e. GR«c,T .. ...301 12100l4, f .. +301 1J)8&68.m.,I _ f.... ncc@iaI. fortll.ll

I II" 24-21. ST P£T ERSB URG4th 1111 Conl rtA on SowwIIi: \', bn_DelaiII:MCrocka. MechE.n&Dcpt.201iloM IiIIL Aubun Um. AllbIlm.AL )6549-0

3501. US.....Td)}4 ~)3IO'f.. l}4I<Wl306 .anad ...crod-.cr@,""",~

J llly )O. AIIpac 2, un:RPOOLINTU~OISt. % - 2Slh AIlIlMnaryCon,.....:Noo... - lbe N",,' 25 Yt ....Dcll ill , lnu'lUlt ofAeo...ua.A,riocuIl1lJ'eHoII.... !I Ual yweli lliU. Sl Albans. lkruAl l lEU UK. Tel ...... 727 I""' S.F.. ...... 727 .!I05!1l

Sq! IU 'M r 1-6. CIIRISTC II URC HROAOS96.loinl AWo~'Z C(lllfftODCO

Oolli l$; ARRB Tranipon Rosoarch , SOOBurwood ll wy,.Vtrmont Slh, Vic 31)) .Tt l .6 Il9B8115'S, Fu -"'(i13 <n87I I04

S.p t.IIIM r l&-ZO.LEUVE:"ONoo.... V,bn1lOC1 EJ>ainetrinIConrtlftlC.Delli la: l SOlrt. K.U 1.c'u,-m-PMA.CdNlJ 3008.}ClOt H..ma:.1k 1I i F )2t6l22917.emall l ~.klllCII..Ul-ac:.bt

Sep t.m Mr U ·2S. ST PETER~Bl1RG

FA.SE S)'IIIpOWm: Tl'UISpOr'l Noi...OcW l$; fAS E Sm"tlary. K-U Leuom- ATf.C.ltslijnml&aol200D.JOO I Leuvao,Bd l,ium.fu. :"' 3l 163279 84.emailjall-Ihotn@fr-.ku\tou'«al- .._bt

Sepct"'Mr 29oO<IoM r Z.BF.l.LEV l,:EI'\OISE-CON96V"'- for1IIe~I 25 YeanOttaUs: EIl~ Pmres.-..ll"nlc.-.

320IF..- A-.- :i ;Staale. WA9810). Td . I 206~3 5.'l9,

f .. · I206!1 0 J)'2

Qd_ber)4, PH ILA DEU'H1 A

4th ""'f Spoh" l.anJUIl'= ProctuDetail. ICSl l'96. sa '" En& Labs.AI du PI>nI Inslltulo. PO Box 269.WiImiftlton.DE I9899 L"SAF.. . 130 2 6SI 6W'.. matl: lCSl P96 @ud.UlkLedu

N" ..mb t r J.6. SAN AI"TO:"OIO1996IEEE lntll;llrUOnicaS ympoliumOtt li ls :J S Scltoonwll d, RO\:kwt lllnlern. ,ional S<;ionco Conter, Mail CodoA9•1049 Camono dos RiO$. Tbolisand Oaks,CA9 I3Ss. USA. F.. ..., 80S 373 4810

:"O..... _btr ll- I5. BIUS BA:"i[· 1 996 AAS Con~

Makin, Endo MteI :""-ationaDd Lc:&ii!auooDetails: R_ hImtr. Tt l 01 l806 t szz.Fu 07 l 806 7m

Dfttolllbtt" 1-6. HO .' OLLU:lr1lJoinl M«tincofWAeousISoac!yofJlIpIIl ud I!loe' A_~ofA>nr;riQ

DtWlI: ASA. SOl) So...aysick 8MI- .~NYII797.llSA.m .'SI6

'76J)77.tmallo~ 0Il

AUSTRAU1N ACOUSTICAl soam

~~'~~~~,......... pl.nealllhKt:

. emP....

:=1~R=llll..(MI._........~....w _

AUSTRALIAN ACOUSTICAL SOCIETY ENQUIRIES

NATIONALMATTERS DIVISIONALMAffiRS w.~~ W ·YlclorllOMtioll' Notitellion o!~d ldd'8SI

E"'l~ .. glrdlngmlmDenhlpPO llo:<l~. POllo."17 Wa~IIl$l PO

'~c1 ~"""~OMW.NEYI07I ME1900 RNE3000

· l'nloHdngs d ......... c:GIlIer«lCII ::.:.,1I&l~1~...IO~~ Se:, W'SThomt ~UrCSeneH

I~SlIlI DMolOnrtl (01) 22!> 1n 2 rtl(03) 19otoon

Ge<>t<li s.cr etlry See,, 1at)' F&ol(07):J76523!i F.. (03l7915t8llMS-ProIMsicWIIICrtrlolAuslrlli.I'lio.-Bigl.0ri'Q..... 2010

W ·HSWlllvlIlClll AJ.S. SAIllvlllon A,l.$-wA Dlvll ionTtIlO2l331 6920 f .. (02j3311296 POllo:<t09O

~c.rrnd""" ~oIWee1l E~WESTPEfI114 san

SOCIETYSUBSCRIPTION RATES Priv" Ilag1. l.Ji'MrMyolMlIIdI

DAAUNGHURST20tO SOlITHAUSTRALIA 5005 Soc:M, T UcM1Ylf llm 1 A,PRI L1WS mernbirohipllJb5cfiplioos

k t.lrO~Soc:C&rll1OO1l/d T"~J3S17 175

MIIb1as lolowl:TtI(02l3:!ll2687

rtl (O!J\ 303301l2 f... (09j:J51 2111f elowllld _ ....H. .. . .. HHH_ ,,__. $81 F"108lXIU3111 _ flt'\@p.-",eu*' Id..,

AIliNle""Subwibl' ",HH'","""" ...... ISif .. , (02)3:!ll206$

•.,..t~S:u:lefII. . _ H__.'HH'_ _ _ _ _ • .....S20

... .,IO,Ea9O'@utl . du,....lelmg.~'de. IdU .'"

ACOUSTICS AUSTRALIA INFORMATION

GENERALBUSINESS PRINTING, ARTWORK ADVERTISINGRATESAavertl llngSu bser1pllont Soo!t Willatnl B&. _...

" MomtArsL.eI{fl Wal"bri 16Cr(WIIJ. PIAl.1/1 Page ..., sec

POe» ~79. CRONULLA2230 ""'"""'''''Tel (02) sea 4362 Tel (02]5235954 VIPage '" 310

fall (0215239631 Fa-. {02) ~3 9637 1/:1Page ees '"1/4Page 22S 210ARTICLES& REPORTS SUBSCRIPTIONRATES 1995 Spotcolour. SIlOper o:olcwsNEWS, BOOK REVIEWS A~' Overseas Pr.parednsert S250 !""_.oI~"", oPOIll

NEWPRODUCTS , ~. AS~ AS '" CoI\111nr~. S15peremi\f3 pwi<nhlThfIEdila 2 ~. AS 82 AS' OO OIacourMd'II .. 1or 3 tonseoJliveadll in~

AcoY$lict AlI5tralia 3 ~. -'$115 A$151Acouslicl &VibralionCtntre

OYerseas subwipti(Q \lQbyailmail SpeeJ.lr" 'I.v.ll.bl.lor4~oIourprln~ ngADFACANBERRA ACT2600 ~... Subterlptlon2O'ro 0lac0unl

Tel(06)2688241 m DiSCOlrillof exbaCOllies Alltnqulrleeto: Mrsleql WBI!bIri;F..- {06}268e276

Aglll1ls di!lCQl,lri 15"'e!$urtace(Ausl) r.ta Te! (02l528436l f a-.{0215239637emaitm-l)urgess@a(lILQl:.lU

I ACOUSTICS AUSTRAUA ADVERTISER INDEX· VOL 23No3 Im OLD . . . . .. . • . .. . . Insert ComputationalM9Chanics ..... .,'" National AcousUc Labs .. . . .. . 112

AcoUSle~ . ... ...... .. ..... .. 108 """"'".... .. . . ..... . . .. . .. 78 Odeon . . . Insert

AcoustieRes.La!ls . . . ... . .. ... 108 ' NCO . . . .. ... 103 p- ....... ...... .. ...... 96

AQJ.~' .... . ... . . .. .. .. . ... 80 ETMC .... . . . InsidsbaclIcoverRTATechnology . . . . .. 103

ASP. ... Insert InSliMe ol AcousliCS . . ...... . lnser1

m Conlerence ... . . .. 108. 112, 115 Irendos . • . .. 96 S."" ..... 80.. . . . . .

~& l<ja8l' . ..... .... . backCQ'o'8l' ."""" .. . . . . . .. lnsideIIOfllCOVllf Tontirl9lndustries . . . • .. . . ... . . . 86

Compumod . .. . . . . ... . . . . .. 96 Matrix .•• .... ..... .. 80 Warbunoo-Franki .. .. . . . . .. . . 104

Acousl lCs A!.lStraha Vol. 23 (1995) No 3 · 116

N!!»Im~@MD!:

IRrcAL·iliViIrc SOIUNID ANAILYSrclR TYlPrc 8~OLarge easy to read 10~ back-lit LCD screen.

Easy to use single level menus and direct keycontrol.

D.1Hz - 20kHz bot h Channels simultaneo usly.

Microph one line and charge input.NORSONIC, G.R.A.S. 8 & K Microphones.

80 oa Dynamic range .

Interna l memo ry: 32000 spectra.

A·, B·, C-. Lin-Frequency weight ings and 4 userdefi ned weighting a.

Inbuilt 3:6" MS-DOS Floppy drive.

Impeccable SCandinav ian des ign.

Options : Signal generato r; revero . time calcula tions. internal Hard Disk drive, Sound Intensity cspaOi/iry.

Measurement, Analysis,Inte rpretation and Reporting

ALL ON YOUR NOTEBOOK:

SOUNDLEVEL METER.

STATISTICAL& FREQUENCYANALYSER(1/ 1·1/3 oct & FFT).

BUILDINGACOUSTICS ANAYLSER.

NOISEMONITOR.

DIGITAL AUDIO RECORDER.

01 DB 'S ACOUSTIC LABORATORY ON A NOTE BOOK.

Til e software is M5-Windows orientate d so mat analysis resu lts are readily copied into W.P.system. Colour can be used extensively for clear easy to read repor ts. t rans parencies and slides.

iE'jj'~© 1T<!')@IJnDll~UCl])~D<e$3 MONTAGUE STREET, BALMAIN NSW204 1

PH: (02) 555 1225

GET A PROFESSIONAL REPORT WITH THENSW: (02)450 2066 VIC.: (03) 9370 7666 om.. (07) 252 5700 WA: (09) 381 4944