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Acoustics lesson 3

8-10-2012 1Herhaling titel van presentatie

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Course overview

Physics of sound Hearing

Measurement of sound

Acoustics in enclosed spaces Transmission of sound sound insulation

Practical noise control principles

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Transmission of sound

Sound reduction index

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The mass-frequency law

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The mass-frequency law

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The mass-frequency law

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The mass-frequency law

Generalization: with wall stiffness

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The mass-frequency law

with

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The mass-frequency law

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The mass-frequency law

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The concidence effect

Concidencecon ition:

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The concidence effect

Concidence frequency?

B EI 3 /12I d l

42sB

c fm

4 2

v vB m

x t

Critical frequency

2crit

c mf

B

64000critf

d c

2(1 )LE

c

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Density E modulus cL f critical (1 cm)

Aluminum 2,7 70 5367,1766 1192,433287

critfd c

, , ,

Concrete 2,5 48 4618,8022 1385,640646

CFRP 1,5 1,5 1054,0926 6071,573108

Coarc 0,18 0,032 444,44444 14400

Glass 2,5 65 5374,8385 1190,733452

Steel 7,8 210 5469,4177 1170,142848

PU 1,2 0,025 152,14515 42065,09242

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The mass-frequency law

Extesion to complex walls:

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The mass-frequency law

SRI:

Thus:

since

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The mass-frequency law

Open surface

Original SRI

n

index

nd

redu

cti

So

Open surface, in m2

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The mass-frequency law

1. Extra transmission loss due to airgap

2. Extra resonance frequencies :1.Wall on air-s rin

2.Acoustic resonance in gap

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Sound transmission loss measurement

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

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Sound transmission loss measurement

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

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Sound transmission loss measurement

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

1 2 1010 log ( )nT

D L L 0 0.5T

S o

nd

1 2 10

A

erschil

Lp,acht

erg

rrectie

Correction of background noise:

V

Lp,bron C

3dB 3

4 tot 5 dB 2

6 tot 9 dB 1

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Sound transmission loss measurement

Rating of airborne sound insulation (ISO 717-1: 1982)

Frequency Ref. va lue

100 33

125 36

160 39

200 42

250 45

315 48

500 52

630 53

800 54

1250 56

1600 56

2000 562500 56

3150 56

In report:

Ref value at 500Hz after correction

Anomalies of more than 8dB

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Sound transmission loss measurement

Contact noise in lab (ISO-6 140: 1978)

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

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Course overview

Course content:

Ph sics of sound Hearing

Acoustics in enclosed spaces

General noise control principles

uropean eg s a on

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Noise control principles

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Noise control principles

Machine noise control procedure:

1. Determine active and passive components2. Airborne, liquid-borne or structural borne

sources?

3. Identify transmission path4. Identif radiatin surfaces

5. Identify primary contributions (of 2. to 4.)

.

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Noise control principles

Source localization

1. Using an intensity

2. Using an acoustic

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Noise control principles

Source localization techniques:

1. Using an intensity meter

2. Usin an acoustic camera micro honearray)

3. Usin lead-foil

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Noise control principles

Airborne sound control:

1. Reduce pressure drop or

outlet flow rate2. Avoid obstacles in the flow

bends, constrictions)

at panels

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Noise control principles

Airborne sound control:

1. Reduce pressure drop or

outlet flow rate2. Avoid obstacles in the flow

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Noise control principles

Airborne sound control:

.flow rate

2. Avoid obstacles in the flow3. Improve geometry (nozzle,

bends, constrictions)

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Noise control principles

Liquid-borne sound control:

1. See airborne sound control2. Prevent cavitation

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Noise control principles

-1. Increase impact time

.

3. Minimize impact mass, increasemass of impacted body

4. Use appropriate gears andbearings

. a ance ro ors an or m n m zerotating mass

.of friction

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Noise control principles

Transmission reduction:. cous c enc osure

2. Use flexible connections

.

4. Use an absorption or reflectionmuffler

5. Use discontinuities in thevibration transmission

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l l

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Noise control principles

Transmission reduction:.

2. Use flexible connections

.

N i l i i l

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Noise control principles

Reflection mufflerTransmission reduction:. cous c enc osure

2. Use flexible connections

.

4. Use an absorption or reflection

Absorption muffler

N i t l i i l

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Noise control principles

Transmission reduction:. cous c enc osure

2. Use flexible connections

.

4. Use an absorption orreflection muffler

5. Use discontinuities in thevibration transmission

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Noise cont ol p inciples

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Noise control principles

Radiation reduction:. se n per ora e p a es w

damping material

Example exam questions

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Example exam questions

Sketch the sound insulation of a wall in function

of the frequency and explain the different parts inthe curve.

Describe how you can measure the transmissionoss etween two rooms.

Give an overview of practical noise controlpr nc p es.