Acoustics lesson 3

Steve VanlanduitSteve Vanlanduit

8-10-2012 1Herhaling titel van presentatie

Course overview

Course content: Course content:– Physics of sound– Hearing– Measurement of sound– Acoustics in enclosed spaces– Transmission of sound, sound insulation,– Practical noise control principles– European legislationEuropean legislation

Transmission of sound

Transmission lossTransmission lossSound reduction index

The mass-frequency law

The mass-frequency law

Exentions:Exentions:1. Oblique incidence:

2. Diffuse incidence:

The mass-frequency law

The mass-frequency law

The mass-frequency lawGeneralization: with wall stiffness

ω

The mass-frequency law

with

The mass-frequency law

The mass-frequency law

The coïncidence effect

Coïncidencedi icondition:

The coïncidence effectCoïncidence frequency?

2/(1 )B EI4 2 2/(1 )B EI 3 /12I d l

42sBc fm

4 2

4 2

v vB mx t

2

Critical frequency2

2critc mf

B

64000crit

L

fd c

2(1 )L

Ec

L

64000Density E modulus cL f critical (1 cm)

Aluminum 2,7 70 5367,1766 1192,433287Lead 11 1 16 1265 544 5057 113801 64000

critL

fd c

Lead 11,1 16 1265,544 5057,113801Concrete 2,5 48 4618,8022 1385,640646CFRP 1,5 1,5 1054,0926 6071,573108Coarc 0,18 0,032 444,44444 14400 L, , ,Glass 2,5 65 5374,8385 1190,733452Steel 7,8 210 5469,4177 1170,142848PU 1,2 0,025 152,14515 42065,09242

The mass-frequency lawExtesion to complex walls:

The mass-frequency law

SRI:

Thus:

since

The mass-frequency lawOpen surfaceOriginal SRI

onin

dex

und

redu

ctio

Sou

Open surface, in m2

The mass-frequency law

Double walls:Double walls:

1. Extra transmission loss due to air gap

2. Extra resonance frequencies : 1.Wall on air-spring1.Wall on air spring2.Acoustic resonance in gap3.Coïncidence frequencies3.Coïncidence frequencies

Sound transmission loss measurement

ISO 140 (1-10): ‘Measurement of sound insulation’ ISO 140-1:1990: lab requirements ISO 140-2:1991: repeatability ISO 140 3 1995 i b d i l ti i l b ISO 140-3:1995: airborne sound insulation in a lab ISO 140-4:1978: airborne sound insulation in-situ ISO 140 6:1978: contact noise of floors (lab) ISO 140-6:1978: contact noise of floors (lab) ISO 140-7:1978: contact noise of floors (in-situ)

ISO 717 : ‘Rating of sound insulation’ ISO 717-1:1982: airborne sound insulation ISO 717 1:1982: airborne sound insulation ISO 717-2:1982: contact noise

Sound transmission loss measurement

Airborne sound insulation in a lab (ISO-3 140: 1995)

Sound transmission loss measurement

Airborne sound insulation in a lab (ISO-3 140: 1995)

Sound transmission loss measurement

Airborne sound insulation in-situ (ISO-4 140: 1978)

1 2 100

10 log ( )nTD L LT

0 0.5T 0T

10log ( )SR L L rond

1 2 1010 log ( )R L LA

ersc

hil

–Lp,

acht

ergr

orre

ctie

Correction of background noise:

VeL p

,bro

n – Co

3dB 34 tot 5 dB 2 6 tot 9 dB 1

Sound transmission loss measurement

Rating of airborne sound insulation (ISO 717-1: 1982)Frequency Ref. value

100 33125 36160 39200 42250 45315 48400 51400 51500 52630 53800 541000 551000 551250 561600 562000 562500 563150 56

In report:• Ref value at 500Hz after correction• Anomalies of more than 8dB• Measurements (corrected and not corrected)• Measurements (corrected and not corrected)

Sound transmission loss measurement

Contact noise in lab (ISO-6 140: 1978)Impact apparatus:Impact apparatus:• 5 hammers of 0.5kg in-line (0.4m)• Free fall of 40mm• Steel cylinder 3cm dia, 50cm radius

Test procedure:• 100ms hammer impacts, hammer impact at 4 locations• SPL in receiving room• Measurement of A• Normalized impact SPL:• Normalized impact SPL:

Course overview

Course content:– Physics of soundy– Hearing– Measurement of soundMeasurement of sound– Acoustics in enclosed spaces– Transmission of sound– Transmission of sound– General noise control principles

E l i l ti– European legislation

Noise control principles

Noise control principles

Machine noise control procedure:1. Determine active and passive components2. Airborne, liquid-borne or structural borne

sources?3. Identify transmission path4. Identify radiating surfacesy g5. Identify primary contributions (of 2. to 4.)6 Use design rules6. Use design rules

Noise control principlesSource localizationtechniques:techniques:1. Using an intensity

metermeter2. Using an acoustic

cameracamera

Noise control principlesSource localization techniques:1. Using an intensity meter2. Using an acoustic camera (microphoneg ( p

array)3. Using lead-foilg

Noise control principles

Airborne sound control:1. Reduce pressure drop or

outlet flow rate2. Avoid obstacles in the flow3. Improve geometry (nozzle, 3. Improve geometry (nozzle,

bends, constrictions)4. Do not point the flow outlet4. Do not point the flow outlet

at panels

Noise control principles

Airborne sound control:1. Reduce pressure drop or

outlet flow rate2. Avoid obstacles in the flow

Noise control principlesAirborne sound control:1 Reduce pressure drop or outlet1. Reduce pressure drop or outlet

flow rate2. Avoid obstacles in the flow3. Improve geometry (nozzle,

bends, constrictions)

Noise control principles

Liquid-borne sound control:1. See airborne sound control2. Prevent ‘cavitation’

Noise control principles

Structure-borne noise control:Structure borne noise control:1. Increase impact time2 Decrease impact speed2. Decrease impact speed3. Minimize impact mass, increase

mass of impacted body4. Use appropriate gears and

bearings5 B l t d/ i i i5. Balance rotors and/or minimize

rotating mass6 Use suitable lubrication in case 6. Use suitable lubrication in case

of friction

Noise control principles

Transmission reduction:1 A ti l1. Acoustic enclosure2. Use flexible connections3 Acoustic screen3. Acoustic screen4. Use an absorption or reflection

muffleru5. Use discontinuities in the

vibration transmission

Noise control principlesTransmission reduction:1 A ti l1. Acoustic enclosure2. Use flexible connections

Noise control principlesTransmission reduction:1 Acoustic enclosure1. Acoustic enclosure2. Use flexible connections3. Acoustic screen3. Acoustic screen

Noise control principlesReflection mufflerTransmission reduction:

1 A ti l1. Acoustic enclosure2. Use flexible connections3 Acoustic screen3. Acoustic screen4. Use an absorption or reflection

muffler

Absorption muffler

muffler

Noise control principlesTransmission reduction:1 A ti l1. Acoustic enclosure2. Use flexible connections3 Acoustic screen3. Acoustic screen4. Use an absorption or

reflection mufflero u5. Use discontinuities in the

vibration transmission

Noise control principles

Radiation reduction:1 R d th di ti f1. Reduce the radiation surface

Noise control principles

Radiation reduction:2 U thi f t d l t ith2. Use thin perforated plates with

damping material

Example exam questions

• Sketch the sound insulation of a wall in functionof the frequency and explain the different parts in the curve.

• Describe how you can measure the transmissionl bloss between two rooms.

• Give an overview of practical noise controli i lprinciples.