Acoustics Electives

7/28/2019 Acoustics Electives

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Architectural acoustics is the science of controlling sound

within buildings. The first application of architectural acoustics

was in the design of opera houses and then concert halls. Morewidely, noise suppression is critical in the design of multi-unit

dwellings and business premises that generate significant noise,

including music venues like bars. The more mundane design of

workplaces has implications for noise health effects. Architectural

acoustics includes room acoustics, the design of recording and

broadcast studios, home theaters, and listening rooms for media

playback.

Building skin envelope

This science analyzes noise transmission from building exterior

envelope to interior and vice versa. The main noise paths are

roofs, eaves, walls, windows, door and penetrations. Sufficient

control ensures space functionality and is often required based on

building use and local municipal codes. An example would be

providing a suitable design for a home which is to be constructed

close to a high volume roadway, or under the flight path of amajor airport, or of the airport itself.

Inter-space noise control

The science of limiting and/or controlling noise transmission from

one building space to another to ensure space functionality and

speech privacy. The typical sound paths are room partitions,

acoustic ceiling panels (such as wood dropped ceiling panels),

doors, windows, flanking, ducting and other penetrations. An

example would be providing suitable party wall design in an


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apartment complex to minimise the mutual disturbance due to

noise by residents in adjacent apartments.

Interior space acoustics

This is the science of controlling a room's surfaces based on

sound absorbing and reflecting properties. Excessive

reverberation time, which can be calculated, can lead to poor

speech intelligibility.

Sound reflections create standing waves that produces natural

resonances that can be heard as a pleasant sensation or an

annoying one. [1] Reflective surfaces can be angled and

coordinated to provide good coverage of sound for a listener in a

concert hall or music recital space. To illustrate this concept

consider the difference between a modern large office meeting

room or lecture theater and a traditional classroom with all hard

surfaces.

Interior building surfaces can be constructed of many different

materials and finishes. Ideal acoustical panels are those without a

face or finish material that interferes with the acoustical infill or

substrate. Fabric covered panels are one way to heighten

acoustical absorption. Finish material is used to cover over the

acoustical substrate. Mineral fiber board, or Micore, is a

commonly used acoustical substrate. Finish materials often

consist of fabric, wood or acoustical tile. Fabric can be wrapped

around substrates to create what is referred to as a "pre-

fabricated panel" and often provides the good noise absorption if

laid onto a wall. Prefabricated panels are limited to the size of the


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reverberation time analysis and nearly400 when transmission lossmeasurements have to be acquiredacross a partition.

Usingserialor sequential frequencyfilters in this situation would be extremelytime consuming so real time or parallelfrequency analyzers are almost alwaysused. The benefits of real

time analysis are the speed at which themultiple data sets can be acquired. This

helps to keep the time on site down to aminimum and the interruptions to anyother persons in the area is alsominimized. Warnings should always begiven to other people when high levels of

steadyor impulsive noise are going tobe generated. The measurements areobtained over all the frequency bands inthe instrument giving a complete picture

from 20 Hz to 20 kHz. The CEL-513Pinknoise generatoris an ideal accessoryfor any of the CEL-500 real timeanalyzers fitted with the buildingacoustics option.

pink noise generator to act

as controllable noise source
http://casellausa.com/en/help/help_s.htm#Sequential%20frequency%20analysishttp://casellausa.com/en/cel/glossary.htm#Serial%20frequency%20analysishttp://casellausa.com/en/cel/glossary.htm#Serial%20frequency%20analysishttp://casellausa.com/en/help/help_r.htm#Real%20time%20analysishttp://casellausa.com/en/help/help_s.htm#Steady%20noisehttp://casellausa.com/en/help/help_i.htm#Impulsive%20noisehttp://casellausa.com/en/cel/bacacces.htm#CEL-513%20Pink%20noise%20generatorhttp://casellausa.com/en/help/help_p.htm#Pink%20noisehttp://casellausa.com/en/help/help_p.htm#Pink%20noisehttp://casellausa.com/en/cel/cel500.htmhttp://casellausa.com/en/cel/bacacces.htmhttp://casellausa.com/en/cel/bacacces.htmhttp://casellausa.com/en/help/help_s.htm#Sequential%20frequency%20analysishttp://casellausa.com/en/cel/glossary.htm#Serial%20frequency%20analysishttp://casellausa.com/en/cel/glossary.htm#Serial%20frequency%20analysishttp://casellausa.com/en/help/help_r.htm#Real%20time%20analysishttp://casellausa.com/en/help/help_s.htm#Steady%20noisehttp://casellausa.com/en/help/help_i.htm#Impulsive%20noisehttp://casellausa.com/en/cel/bacacces.htm#CEL-513%20Pink%20noise%20generatorhttp://casellausa.com/en/help/help_p.htm#Pink%20noisehttp://casellausa.com/en/help/help_p.htm#Pink%20noisehttp://casellausa.com/en/cel/cel500.htmhttp://casellausa.com/en/cel/bacacces.htmhttp://casellausa.com/en/cel/bacacces.htm


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Measurements consist of finding thetransmission loss across a part of thebuilding elements such as party walls orfrom a floor through a ceiling. Noise

sources typically used arepink noisegenerators which produce noise energyover the whole audio bandwidth ofinterest. This broadband signal is fed intoa high power amplifier and loudspeakerso that accurately controlled noise levelsmay be produced. The real timeanalyzerturns the noise source on andoff at the right time and uses special

switching signals to gather the correctmeasurements for the analysis of the rawdata. As an alternative, a high noise levelimpulse is often used as the stimulussignal. This type of noise source has theadvantage of being easier to carry aroundand can be generated from a

starting pistol or a helium balloon but thenoise level produced may not containenough energy at all the frequencies ofinterest. Impulses generated like this arealso somewhat variable in output and somay not trigger the data capture reliablyand correctly every time.

measuring the reverberationtime in a room

Spectral noise levels are required on bothsides of a common party wall or from

outside to inside when assessing theimpact of traffic noise on a buildingfacade. Frequencies cover the range from100 Hz up to 4 or 5 kHz typically whencarrying out the measurements tointernational standards. Methodologiesare laid down in manyISO andASTM
http://casellausa.com/en/help/help_t.htm#Transmission%20loss%20(dB)http://casellausa.com/en/help/help_p.htm#Pink%20noisehttp://casellausa.com/en/help/help_p.htm#Pink%20noisehttp://casellausa.com/en/cel/glossary.htm#Broadbandhttp://casellausa.com/en/help/help_r.htm#Real%20time%20analysishttp://casellausa.com/en/help/help_r.htm#Real%20time%20analysishttp://casellausa.com/en/help/help_i.htm#Impulsive%20noisehttp://casellausa.com/en/help/help_f.htm#Frequencyhttp://casellausa.com/en/cel/glossary.htm#Frequencyhttp://casellausa.com/en/help/help_i.htm#ISOhttp://casellausa.com/en/help/help_a.htm#ASTMhttp://casellausa.com/en/help/help_t.htm#Transmission%20loss%20(dB)http://casellausa.com/en/help/help_p.htm#Pink%20noisehttp://casellausa.com/en/help/help_p.htm#Pink%20noisehttp://casellausa.com/en/cel/glossary.htm#Broadbandhttp://casellausa.com/en/help/help_r.htm#Real%20time%20analysishttp://casellausa.com/en/help/help_r.htm#Real%20time%20analysishttp://casellausa.com/en/help/help_i.htm#Impulsive%20noisehttp://casellausa.com/en/help/help_f.htm#Frequencyhttp://casellausa.com/en/cel/glossary.htm#Frequencyhttp://casellausa.com/en/help/help_i.htm#ISOhttp://casellausa.com/en/help/help_a.htm#ASTM


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standard documents. Reference should bemade to these standards to ensure thatthe correct measurement results arecollected before leaving site so that the

calculations can be carried out whenresults have been transferred to a laptopcomputer. Special software is available toperform these calculations according tothe appropriate methods for each task.

Building acoustics

The sound absorption coefficient of a material is = (1 r),where r, the sound energy reflection coefficient, is the ratioof sound energy reflected from the surface of the material to thatincident upon it. Values for a specific material depend uponfrequency and upon the angle of incidence of the sound. When

the sound field is approximately diffuse the correspondingquantity is denoted by s; this may be determined in accordancewith BS 3638:1987. The values in the table overleaf have beentaken from Evans and Bazley (1978) which predates the currentstandard. Absorption depends on mounting and other details ofconstruction and the following values should be regarded only astypical.

Reverberation absorption coefficients

Material Thick

Frequency/Hz


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ness(m

m)

125

250

500

100

0

200

0

400

0

Acoustic plaster . . . . . . . . . . . . 13

0.15

0.20

0.35

0.60

0.60

0.50

Acoustic tiles (perforated fibreboard) . . 18

0.

10

0.

35

0.

70

0.

75

0.

65

0.

50

Asbestos (sprayed). . . . . . . . . . . 25

0.10

0.30

0.65

0.85

0.85

0.80

Brickwork . . . . . . . . . . . . . .

0.02

0.02

0.03

0.04

0.05

0.07

Carpet (Axminster) . . . . . . . . . . 8

0.05

0.15

0.30

0.45

0.55

Carpet on underlay . . . . . . . . . .14

0

.05

0

.20

0

.40

0

.60

0

.65

Curtain (velour, draped) . . . . . . . 0

.0.

0.

0.

0.

0.


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14

35

55

72

70

65

Glass fibre (resin-bonded) . . . . . . 250.10

0.25

0.55

0.70

0.80

0.85

Glass wool (uncompressed) . . . . .25

0.10

0.25

0.45

0.60

0.70

0.70

Mineral wool . . . . . . . . . . . . 25

0.10

0.25

0.50

0.70

0.85

0.85

Polystyrene, expanded (rigid backing) 13

0.05

0.05

0.10

0.15

0.15

0.20

Polystyrene, expanded (on 50 mm battens) 13

0.05

0.15

0.40

0.35

0.20

0.20

Polyurethane foam(flexible)gdsghdsgdgdgsgdgsagdgdgfdhgfhdhHBSHGFHSBABFHGSHBFBHGHSDBFHDSBHFJBDSHBFGD

HSJGBHDSBVGBDSHJNFJBHSGAHFSAHGFHSABHGFHSABFG

50

0.

25

0.

50

0.

85

0.

95

0.

90

0.

90

Snow . . . . . . . . . . . . . . . 25 0.1

0.4

0.6

0.7

0.8

0.8


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5 0 5 5 0 5

Wood panelling (oak, on 25 mm battens) 13

0

.20

0

.10

0

.05

0

.05

0

.05

0

.05

Insulation against airborne noise. The sound reductionindex (R) is the ratio of sound energy incident on a partition tothat which is transmitted through it, expressed in decibels (BS2750: 1980). The values vary with frequency and angle of

incidence; for comparative purposes a single value (Rw) can bederived from the data over the frequency range 1003150 Hzaccording to BS 5821: Part 1: 1984. Although mass is the maindeterminant ofRabove the resonant frequency, the relationshipis not a simple one, due to coincidence effects associated withflexural waves in the partition (Fahy 1985). For single,homogeneous partitions, however, the mean value ofRover therange 1003150 Hz can be estimated to be approximately Ravg=10 + 15 log10(m) dB, where m is the surface mass density in

kgm

2

. For some types of partition Rw Ravg + 3 dB. The tableopposite gives laboratory values ofRand Rw obtained at theBuilding Research Establishment and the Building Test Centre ofBritish Gypsum Ltd (Dr L. C. Fothergill, private communication).

Sound Reduction Indices (dB)

Type ofelement

Mass

1

Octave BandCentreFrequency/Hz

3

RwdB


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kg/

m2

10

0

12

5

16

0

20

0

25

0

31

5

40

0

50

0

63

0

80

0

10

00

12

50

16

00

20

00

25

003150

1Thermaldoubleglazing

2223 1917 21 26 2830 32 33 33 32 30 28 30 33 30

(6-12-

6),timberframe

2

As 1,plus 4mmsecondary pane

3530 3127 32 38 4044 47 49 49 44 41 43 43 45 42

spaced150mm,reveallined

with

absorbent

3 Brick,100 mmthick,no

20033353334343336394244 46 48 49 51 52 53 44


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finish

4

Lightwei

ghtaggregate

26015131515141517171920 22 23 27 28 31 37 22

blockwork 215mmthick,no

finish(permeableblock)

5

As 4withplasterfinish

both

28036313335384247495255 59 61 63 65 66 67 51

sides

6

Twoleaves100 mmblockwork,

39028273133353541424752 55 59 63 66 69 70 46

50 mm


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cavity,

nofinish

7

As 6withplasterfinishboth

41041373738384146495459 63 67 72 76 79 82 52

sides

8

Twoleaves100 mmaerated

13335404444434242414449 53 58 61 64 66 71 50

concreteblockwork, 50

mm

cavity,nofinish

9

As 8

withplasterfinishboth

15337424643383840434751 56 60 66 68 71 76 49

sides


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10

Floor18 mmchipboa

rd

1915 2025 28 29 3437 37 42 43 44 44 42 40 41 38

194 45 mmjoists at450 mm

centres,12.5mmplasterboard

ceiling

11

As 10but 600mmjoist

spacing

1726 3238 35 35 3737 41 45 47 49 51 49 45 40 42

12

12.5mmplasterboardsheet

11.8

21212325252628282931 33 34 35 35 29 26 31

13

12.5

mmplasterboardeachside

17182737342735333737 42 46 48 49 46 38 38


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of 75mm 38 mm

timberstuds

14

As 13with 25mmmineralwool

13152835313237374243 47 50 53 53 46 41 40

incavity

15

As 14with nolayersof

24243342353742444748 51 54 57 58 52 48 46

plasterboard

eachside

1

6

Twoleavesof 12.5mm +19 mm

43475556596467717272 75 80 83 84 86 86 70

plasterboard onmetalstuds,

separat


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ed by250 mmcavity

with100 mmmineralwool

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Acoustics Electives