noise control acoustic units presentation

8/8/2019 Noise Control Acoustic Units Presentation

1/19

BASIC NOISE TERMINOLOGYBASIC NOISE TERMINOLOGY

NZIEH CONFERENCENZIEH CONFERENCECHRISTCHURCH 2009CHRISTCHURCH 2009

ViaStrada LimitedViaStrada Limited


2/19

serves little or no purpose for the exposedserves little or no purpose for the exposed

unwanted soundunwanted sound -- (NZS 6802:2008)(NZS 6802:2008)


3/19

Frequency is expressed in Hertz (Hz) i.e. cycles per secondFrequency is expressed in Hertz (Hz) i.e. cycles per second(number of wavelengths passing a point in one second)(number of wavelengths passing a point in one second)e. . 1 Hz = 1 c cle/second 500 Hz = 500 c cles/seconde. . 1 Hz = 1 c cle/second 500 Hz = 500 c cles/second


4/19

Sound frequenciesSound frequencies from approximately 20 Hz tofrom approximately 20 Hz to20,000 Hz20,000 HzSpeech is about 400 to 5000 HzSpeech is about 400 to 5000 Hz

,,

Birds chirping, cicadas are above 5000HzBirds chirping, cicadas are above 5000Hz

over 100 pascals (100 million micropascals)over 100 pascals (100 million micropascals)


5/19

Using decibels allows us to handle the huge range of soundUsing decibels allows us to handle the huge range of soundpressure values more easilypressure values more easily

A decibel is a logarithmic unit of measurement used to expressA decibel is a logarithmic unit of measurement used to expresssound pressure levels, with 20 micropascals as the referencesound pressure levels, with 20 micropascals as the reference

For the mathematically inclined:For the mathematically inclined:

A decibel is ten times the logarithm to the base 10 of the ratio of theA decibel is ten times the logarithm to the base 10 of the ratio of thesquare of the sound pressure to the square of the reference value.square of the sound pressure to the square of the reference value.

10 lg(p10 lg(p22/p/p0022) dB (NZS 6801:2008)) dB (NZS 6801:2008)

(reference value p(reference value p00= 20 micropascals)= 20 micropascals)


6/19


7/19

1 plus 1 = 3!1 plus 1 = 3!(Adding two equal sound sources raises the level by 3 dB)(Adding two equal sound sources raises the level by 3 dB)

e.g. 50 dB + 50 dB = 53 dBe.g. 50 dB + 50 dB = 53 dB

If the difference between the two sound sources is 10 dBIf the difference between the two sound sources is 10 dBor more, there is no increase:or more, there is no increase:50 dB + 48 dB = 52 dB50 dB + 48 dB = 52 dB

50 dB + 44 dB = 51 dB50 dB + 44 dB = 51 dB

50 dB + 40 dB = 50 dB50 dB + 40 dB = 50 dB


8/19

pressure levelpressure level

22 or 3 dB chan e is ust erce tibleor 3 dB chan e is ust erce tible 5 dB is noticeable5 dB is noticeable

20 dB change sounds 4x as loud20 dB change sounds 4x as loud 40 dB change40 dB change soundssounds 8x as loud etc8x as loud etc


9/19

Noises at different frequencies are perceived differentlyNoises at different frequencies are perceived differently uman ear ng a usts or we g ts ower requenc esuman ear ng a usts or we g ts ower requenc esso that they dont sound as loud as higher onesso that they dont sound as loud as higher ones

n soun eve me ers, requenc es are we g en soun eve me ers, requenc es are we g e(attenuated) in a similar way to our own hearing(attenuated) in a similar way to our own hearing

,,and is used in most noise standards in District Plansand is used in most noise standards in District Plans

instantaneous loud noises such as blastinginstantaneous loud noises such as blasting


10/19

Picture source: Bruel and KjaerPicture source: Bruel and Kjaer


11/19

distance from the sourcedistance from the source

Point source e. . enerator :Point source e. . enerator : 6 dB er doublin of distance6 dB er doublin of distance Line source (e.g. road):Line source (e.g. road): 3 dB per doubling of distance3 dB per doubling of distance

air absorptionair absorption

buildings and other barriersbuildings and other barriersmeteorological conditionsmeteorological conditions

But ground or water surface reflection and wind canBut ground or water surface reflection and wind can

High frequencies are easier to shield by buildings andHigh frequencies are easier to shield by buildings andbarriers than low fre uencies i.e. bassbarriers than low fre uencies i.e. bass


12/19

TermTerm NZS6801:2008NZS6801:2008

symbolsymbol

Previous NZSPrevious NZS

version symbolsversion symbols

Decibel (dB)

A or C weighting

Maximum noise level

dB LAFMAX

dBA Lmax10 Percentile level dB LA10 dBA L10

Background noise level dB LA90/dB LA95 dBA L90/dBA L95

Equivalent sound level dB LAeq(t) dBA Leq

oun exposure eve AE

Peak sound level dB LCpeak LPeak


13/19

Noise arameters:Noise arameters:LeqLeq

Aeq(t)Aeq(t) The timeThe time--average Aaverage A--weighted sound pressure levelweighted sound pressure level

e eve o s ea y no se w c wou con a n ee eve o s ea y no se w c wou con a n e

same sound energy as all the noise variations over thesame sound energy as all the noise variations over the

Can be used for a variety of noise types (steady,Can be used for a variety of noise types (steady,fluctuatin etcfluctuatin etc

Good correlation with annoyance studiesGood correlation with annoyance studies Acce ted and a lied universallAcce ted and a lied universall


14/19

dBLdBLA10(t)A10(t) -- the L10the L10

The level met or exceeded for 10% of the measurement intervalThe level met or exceeded for 10% of the measurement interval Widely used in District Plans to control a variety of noise situations, butWidely used in District Plans to control a variety of noise situations, but

more appropriate for steady noisemore appropriate for steady noise

Will be replaced by LWill be replaced by L

AeqAeqas District Plans are gradually updated to includeas District Plans are gradually updated to include

2008 versions of NZS6801 and 68022008 versions of NZS6801 and 6802

A90(t)A90(t) -- the L90the L90

The background noise levelThe background noise level the level met or exceeded for 90% of thethe level met or exceeded for 90% of the

measurement ntervameasurement nterva

L95 used in earlier versions of NZ Acoustic StandardsL95 used in earlier versions of NZ Acoustic Standards


15/19


16/19

,100

90

70

80

Lmax

60

dBA

L10

L90Leq

50

30

40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Measurement periods


17/19

dB SELdB SEL or dBLor dBL

,,second, would convey the same sound energy as asecond, would convey the same sound energy as a

iven noise eventiven noise event

i.e. the energy of the event is normalised to 1 secondi.e. the energy of the event is normalised to 1 secondAllows the Le from a number of similar discreteAllows the Le from a number of similar discrete

noise events (e.g. car or aircraft movements) to benoise events (e.g. car or aircraft movements) to be

calculated for any assessment periodcalculated for any assessment periodAllows the sound energy from different events to beAllows the sound energy from different events to be

comparedcompared


18/19

LdnLdn

= Leq= Leq (24 hours)(24 hours) with 10 decibels added during thewith 10 decibels added during then g t per o ecause n g tn g t per o ecause n g t--t me no se events aret me no se events aremore annoyingmore annoying

== --

Ln = Leq (9 hrs) + 10dB between 2200 and 0700 hrsLn = Leq (9 hrs) + 10dB between 2200 and 0700 hrs

Adding 10dB over the night period penalises any noiseAdding 10dB over the night period penalises any noise

event during that periodevent during that period e.g. one night flight = 10 day flightse.g. one night flight = 10 day flights


19/19

Russell MalthusRussell MalthusSenior Environmental Health ConsultantSenior Environmental Health Consultant

ViaStrada LimitedViaStrada [email protected]@viastrada.co.nzwww.viastrada.co.nzwww.viastrada.co.nz

noise control acoustic units presentation

Documents