ar2ae045-ra2 room acoustics 2

8/17/2019 AR2AE045-RA2 Room Acoustics 2

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OOM ACOUSTICS ROOM ACOUSTICS ROOM ACOUSTICS ROOM

Acoustics

Lecture AR2AE045-RA2

Martin Ten ierik

DR. IR. ARCH. MARTIN TENPIERIK / FACULTY OF ARCHITECTURE / BUILDING PHYSICS / AR2AE045 / 01 February 2012 / 1


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Room Acoustics



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Thousands ofRays!

longer path

later arrival

“ reverberation"

direct sound

microphone




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Echogram

direct

echolog-

scale

0.6 s

20 dB

me ax s




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ReverberationTime

Sabine versus Eyring

Sabine:

0

.

6

tot tot

T Ac S

Eyring:

0

.

ln 1 6 ln 1

tot tot

T

c S S

- Note the minus sign in Eyring’s equation- Differences are small if is small

- Differences become bigger if approaches 1




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90

SoundPressure

Sabine-Franklin-Jäger theory

70

75

80

[ d B ]

0.02

0.050.10

0.20

55

60

65

S P L ,

L

p 0.50

1.004 1

40

45

0 2 4 6 8 10 12

210 log

4 p W L L

r A

distance from source [m]




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90

SoundPressure

Corrected Sound Pressure Level

70

75

80

[ d B ]

0.02

0.050.10

0.20

55

60

65

S P L ,

L

p

0.50

1.00/

4 11 r mfp

40

45

0 2 4 6 8 10 12

2og

4

p W r A

distance from source [m]




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S/N ratio Signal to noise ratio is then defined as

2/ 10 log 10 log4S N r A

S/N depends on:

- number of noise sources in the room n

- total absorption (including guests) A - mean absorption coefficient




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(Ra)STI (Rapid) Speech Transmission Index

L p STI

• Currently is the best predictor for speech

intelligibility49 dB 47%

- It considers speech with its variations in frequency

and intensity Intensity is modulated

‘ ’

45 dB 64%

53 dB 78%

frequencies

- It includes the influence of the transfer path (=room) background noise and reverberation

• However is tedious to measure on site


• But is easily calculated with simulation software



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Speech Male speech

Female speech




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AuditoriumAcoustics

With pencil and paper a good estimate of a concerthall can be made (70% ???)

Modern simulation software is an important tool

For arge au itoriums sti p ysica mo e s are ma e

and tested (90% ???)

The remaining 10% is pure psychology, PR and luck.




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Room Acoustics




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ISM (1) Image Source Model uses mirror sources behind wall

microphone

r 0

r

source mirror source


x x



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ISM (2) Sound pressure caused by direct sound

microphone

r 0

r

mirror sourcesource source

2 0 0 sourcec W


; 204

eff dir r



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ISM (3) Sound pressure resulting from the reflected soundcan be considered coming from the mirror source.

microphone

r 0

r

Wsource

mirror sourcesource

0 02 1 sourcec W


; 24

eff refl r



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ISM (4) Extended to a room with multiple mirror sources.Infinitely many mirror sources can theoretically be taken.They all add to the total sound pressure but the further

,

the more of its energy is absorbed.




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ISM (5) The Image Source Model is very suitable forcomputerised calculations. You only need to specify:

•geometry and

•absorption coefficients

However, the model has difficulties coping with

•complex geometries and

•diffuse reflection of sound waves




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ISM (6) Eyring used the Image Source Model for deriving hisreverberation time, T eyr.

After a certain time, reflections from many directions

w con r u e o e soun pressure n a rece ver

position. We can then say that all walls have the

avera e absor tion coefficient .

= o .




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ISM (7) So, if r i >> mfp , then the expected number ofreflections equals

4 i i tot

r r S n

mfp V

The sound pressure in the receiver position comingrom t is i mirror source t en equa s

8

1

i tot r S

V

; 0/ refl ii

p g t r cr




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ISM (8) … and the effective pressure squared averaged overa time interval t

4

2

; 21

i tot r

V

refl iG p

G = the sound energy of the source [W]

i




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ISM (9) It can be proven that the total number of sourcesthat within an interval t adds to sound pressure in

r v r u

3204 c

V

= t e time rom t e moment o emission o t e

source pulse [s]




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ISM (10) Provided that t >>1/r 0 and the sources areuncorrelated, combining the previous two equations

v

0

2 0 44( ) 1

tot

c S

V c G p

For a 60 dB decrease in sound pressure level =T

0

4

60 10 lo 1

tot c TS

V




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ISM (11) Previous equation can be rewritten to

55.3 V

0 ln 1

tot c S

which is Eyring’s reverberation time equation.




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Room Acoustics




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Ray Tracing (1) Ray truncation time is the time

.

source

microphone

Ray Tracing is another technique to calculate the

response of a room. Rays emitted from the source


.



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Ray Tracing (2)

source

microphone

Each ray (flat progressing wave) is emitted in a

certain direction.




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Ray Tracing (3)1 degree spacing is for

instance 10000 rays/oct.

microphone

The source is characterised by a spatial distribution

of rays to be emitted.




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Ray Tracing (4)

microphone

When a ray hits a wall, part of it is absorbed ( ),

part of it specularly reflected ((1- )(1- )), and part


- .



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Ray Tracing (5) When a ray hits a wall it is absorbed and reflected

=

= diffusion coefficientW

W

(1) W

W




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Ray Tracing (7)

microphone

Receiver needs to have a certain random size.

Otherwise the chance that a ray hits the receiver


.



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Ray Tracing (8)

microphone

Alternative is ray tracing with cone tail correction.

The receiver is hit if it falls inside the cone of the


.



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Ray Tracing (9) Ray Tracing is very suitable for computerisedcalculations. Advantages are:

•complex geometry can be handled

•diffuse reflection can be handled

•directivity of sources can be included by adding

weight factors to the rays emitted

Disadvantage:

•sharp boundary between hitting or missing receiver

solution: cone tail correction.




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OO COUS CS OO COUS CS OO COUS CS OO

Room Acoustics

Catt Acoustic




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CATT Acoustic CATT ACOUSTIC

www.catt.se

Demo version of program can be downloaded

Full version available on computers in BT-lab

“shoebox” model available




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CATT Acoustic

MJT




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CATT Acoustic

MJT




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CATT Acoustic 3D CATT Acoustic model

MJT




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CATT Acoustic Echogram at 500 Hz

MJT




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CATT Acoustic T -30 at 500 Hz - room average: 1.96 ± 0.08 s.

MJT




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CATT Acoustic G mid - room average: 5.4 ± 1.1 dB.

MJT




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CATT Acoustic 3D CATT Acoustic model of student work places

Kevin vd Weijden




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CATT Acoustic T -30 and STI for different acoustic measures

3,5 [ s ]

Kevin vd Weijden

1

1,5

2

2,5

e r b e r a t i o n T i m e

0

0,5

1 2 5

2 5 0

5 0 0

1 0 0

0

2 0 0

0

4 0 0

0

Frequency [Hz]

R e

60

70

80

90

100

T

I [ % ]

0

10

20

30

40

7

S


Distance to source [m]



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CATT Acoustic [Live demonstation using the shoebox model]




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Room Acoustics




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‐ opdracht Bouwfysica na de verbouwing

‐ gebouw

‐ warmte

&

vocht

‐ akoestiek

‐ licht

Akoestiek

• Weglaten plafonds grote gevolgen

• Vloerbedekking niet afdoende geluidabsorberend

‐ enquête

‐ conclusies

• ersc en e maa rege en ge es

• Meer maatregelen in de planning

(met name

gordijnen)

DR. IR. ARCH. MARTIN TENPIERIK / FACULTY OF ARCHITECTURE / BUILDING PHYSICS / AR2AE045 / 01 February 2012 / 45D. Bankersen & L.M. Schaberg

Building Technology: Climate Design and Research Vrijdag 27‐03‐2009


Akoestiek meter


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‐ inleiding

Akoestiek meter Opstelling

‐ ge ouw

‐ warmte

&

vocht

‐ Akoestiek

‐ theorie

‐ werkwijze

‐ resultaten

‐ bespreking

‐ conclusies

‐ c t

‐ enquête

‐ conclusies

Meetpunten





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‐ inleiding

‐ ge ouw

‐ warmte

&

vocht

‐ Akoestiek

‐ theorie

Zaal S

‐ werkwijze

‐ resultaten

‐ bespreking

‐ conclusies

‐ c t

‐ enquête

‐ conclusies

02oost700





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Assignment Task 1 is to get the ‘shoebox’ model working and toget an understanding of the program!

- Example: shoebox

- y u r ru ur

- Look at the calculation possibilities of Catt Acoustic

- Run a full detailed calculation

- Interpret results

This part is not for the report!!!




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Assignment Acoustic Comfort in BK-City

.-Choose a small lecture room inside

BK-City:

*It should have a simple geometry

*It must be an uncoupled room*Preferably one of the rooms

measured by Bankersen and Schaberg

*rock might be interesting

*We will also measure ‘het Ketelhuis’




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.

-Measure the reverberation time and

background noise (L eq ) at several

positions inside room (125-4k Hz)

*four positions (one at the back of theroom; wo a a s ance equa o m p

from source; one at 1 m from source).

*room and the materials used.

*analyse the acoustics of the room


using the measurements



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.

-Make a model in Catt Acoustic

*Create .geo, src.loc and rec.loc-files

*Use an omni-directional sound source

*Create receivers at the measurementpoints

*Specify absorption coefficients from

*Take default diffusion coefficients

30%




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.-Validate your model with the

measured RT values

*If differences are too big, modify the

input values of the absorption

coefficients until ou find the model

sufficiently accurate.




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.

-Do a hand calculation of T, G and

S/N

*Do this for all receiver positions

-Do a full detailed calculation withCatt Acoustic with the final model

-Compare the results for T and G ofboth calculations




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.-Analyse now the room for speech

*Use the calculated S/N values (byhand -6 dBbad 0 dBfair +6 dBgood; +15 dBexcellent)

*Use the calculated STI values (bycomputer) (0.75excellent)

*Use the calculated and measured T -30 values (T -30 should be near 0.8 s.)




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.-Analyse now the room for speech

*Is it a good lecture room?

- no , ow can e mprove ointo detail here.

- n wr te a report




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That’s it for today!End

You can work on the assignment on Friday’s.

r ep n e morn ng measuremen s

09:00 in room 01.West.060



Fri 8 Okt in the afternoon individual appointments

ar2ae045-ra2 room acoustics 2

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