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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.
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