chapter 18 sound transmission jean-louis...

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 1

Chapter 18Sound transmissionJean-Louis Migeot

1. Sound transmission and insulation: definitions and measurement techniques

2. Low frequency model: rigid panel on elastic support

3. High frequency model: mass law and coincidence

4. General model

5. Double walls

6. Some comments

7. Application to a windshield

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 2

Chapter 18Sound transmissionJean-Louis Migeot

1. Sound transmission and insulation: definitions and measurement techniques

2. Low frequency model: rigid panel on elastic support

3. High frequency model: mass law and coincidence

4. General model

5. Double walls

6. Some comments

7. Application to a windshield

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 3

Some Terminology

Reflection - Absorption Transmission - Insulation Refraction

Radiation Scattering Propagation - Attenuation

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 4

Acoustic Transparency

➢ Acoustic transparency generally defines the ability of a component to isolate a volume from external noise sources

➢ The standard tests of acoustic transparency generally involve 2 rooms acoustically connected by the system to be tested

➢ The typical indicator used for acoustic transparency is the Transmission Loss index (TL)

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 5

Transmission Loss

Reverberant Room

with Diffuse Sound FieldAnechoic Receiving

Room

Measurement of

Radiated Power

Measurement of

Incident Power

Partition

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 6

What is the transmission loss index?

➢ Transmission loss:

Symbols used in the literature: TL, STL or R

expressed in dB

Intrinsic property of system (does not depend on the coupled rooms of the set-up)

with

➢ The transmission loss is the logarithmic representation of the ratio of powers: What part of the incident power is transmitted through the structure ?

dBTL )1(log10 10 =

incidentdtransmitte WW /)( =

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 7

Typical Measurement Set-up (1)

➢ Anechoic and reverberant rooms can be associated: side by side (classic transmission loss measurements) or on top of each other (building impact noise).

➢ Most used set-up: two side-by-side reverberant rooms

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 12

Typical variation of TL with frequency

Resonancescontrolled

St

iffn

ess

con

tro

lled

Mass law

Coincidence

Asymptoticmass law

Low damping

High damping

TL –

Tra

nsm

issi

on

Lo

ss

Frequency (log f)

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 13

Chapter 18Sound transmissionJean-Louis Migeot

1. Sound transmission and insulation: definitions and measurement techniques

2. Low frequency model: rigid panel on elastic support

3. High frequency model: mass law and coincidence

4. General model

5. Double walls

6. Some comments

7. Application to a windshield

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 14

Elastically mounted rigid panel

X

Incident

Reflected

Transmitted

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Transmission coefficient

Normal velocity continuity:

Dynamic equations

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Transmission coefficient (Ctd)

Transmission coefficient:

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 17

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70 80 90 100

k=10.000, m=1

k=20.000, m=1

k=10.000, m=2

k=10.000, m=1, c'.10

k=10.000, m=1, c'/10

Sensitivity to stiffness and mass

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 18

Chapter 18Sound transmissionJean-Louis Migeot

1. Sound transmission and insulation: definitions and measurement techniques

2. Low frequency model: rigid panel on elastic support

3. High frequency model: mass law and coincidence

4. General model

5. Double walls

6. Some comments

7. Application to a windshield

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 19

Infinite flexible plate

qq

X

Y

q2

Normal velocity continuity:

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 20

Dynamic equations of the plate

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Attenuation

Consider two identical fluids:

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Insulation curves

0

20

40

60

80

100

120

140

100 1,000 10,000 100,000

15°

30°

45°

60°

q

q

Coincidence: damping control

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 23

Free bending waves in an infinite plate

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 24

Coincidence

q

Coincidence occurs when

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Coincidence frequency / incidence

Free bending waves:

Coincidence angle:

Coincidence frequency:

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 26

Coincidence

q1

(b)

q2

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 27

Transmission under diffuse incidence

0.0000E+00

2.0000E+01

4.0000E+01

6.0000E+01

8.0000E+01

1.0000E+02

1.2000E+02

100 1000 10000

Champ diffus

Incidence normale

Incidence oblique 45°

6dB/oct.

contrôle par la masse

9dB/oct.

contrôle

par la r

igidité

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 28

Chapter 18Sound transmissionJean-Louis Migeot

1. Sound transmission and insulation: definitions and measurement techniques

2. Low frequency model: rigid panel on elastic support

3. High frequency model: mass law and coincidence

4. General model

5. Double walls

6. Some comments

7. Application to a windshield

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 29

Transmission through finite baffled plates

x

z

y

baffleplaque

1

2

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 30

Finite vs. infinite plate models

Frequency (Hz)

Finite plate model

Infinite plate model

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 31

Typical variation of TL with frequency

Resonancescontrolled

St

iffn

ess

con

tro

lled

Mass law

Coincidence

Asymptoticmass law

Low damping

High damping

TL –

Tra

nsm

issi

on

Lo

ss

Frequency (log f)

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 32

Chapter 18Sound transmissionJean-Louis Migeot

1. Sound transmission and insulation: definitions and measurement techniques

2. Low frequency model: rigid panel on elastic support

3. High frequency model: mass law and coincidence

4. General model

5. Double walls

6. Some comments

7. Application to a windshield

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 33

Double-walls – Mass-air-mass resonance

m1=rvh1

Resonance frequency:

m2=rvh2

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 34

Double-walls

I R

T

M1 M2

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Coincidence 1

Coincidence 2

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 36

Chapter 18Sound transmissionJean-Louis Migeot

1. Sound transmission and insulation: definitions and measurement techniques

2. Low frequency model: rigid panel on elastic support

3. High frequency model: mass law and coincidence

4. General model

5. Double walls

6. Some comments

7. Application to a windshield

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 37

Real vs. ideal structures

Figure 1. Transmission losses of typical single-leaf walls, A: 16 mm plywood, 10 kg/m², STC 21; B: 13 mm wallboard, 10 kg/m², STC 28; C: 1.3 mm steel, 10 kg/m², STC 30; D: 100 mm concrete, 235 kg/m², STC 52. Credit: A.C.C. Warnock.

Figure 2. Effect of air space on ideal double walls with 0.5 mm steel on each face, sound absorbing material in the cavity and no rigid mechanical connections between the faces. A has an airspace of 100 mm, a resonance dip at 135 Hz, and an STC of 29; B has an airspace of 5 mm, a resonance dip at 630 Hz, and an STC of 24. Curve C represents mass law predictions for a single 1 mm steel sheet and has an STC of 28. Credit: A.C.C. Warnock.

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 38

Weak link principle of acoustic insulation

1.5 mx

2.5 m

1mm gap

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 39

Airborne vs. structure-borne transmission in buildings

From Vèr & Sturz in Harris C.M., Handbook of Acoustical Measurements and Noise Control, McGraw Hill, New-York, 1991

Airborne transmission Structure borne transmission

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 40

Chapter 18Sound transmissionJean-Louis Migeot

1. Sound transmission and insulation: definitions and measurement techniques

2. Low frequency model: rigid panel on elastic support

3. High frequency model: mass law and coincidence

4. General model

5. Double walls

6. Some comments

7. Application to a windshield

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 41

Windshield transmission

Glass Glass

CeramicPVB

Car

Exterior

Car

Interior

Absorption

Transmission

Acoustic Transmission Path

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 42

Correlation or simulations with measurements: NSG

➢ Measurement following ISO 140

Reverberant

room

Anechoic Room

Test Piece :

single layer glass

Nippon Sheet Glass

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 43

Correlation or simulations with measurements: Glaberbel (AGC)

T ransparence acoust ique - Comparaison simulat ions ACT R AN/mesures

BMW Sér ie 3

-10

-5

0

5

10

15

20

25

30

35

40

0 20

0

40

0

60

0

80

0

10

00

12

00

Fréquence [Hz]

Tra

nsm

issi

on

Lo

ss (d

B)

ESSAI 1 ESSAI 2 ACT RAN

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 44

20

25

30

35

40

45

50

100 1000 10000

Frequence (Hz)

TL

(d

B)

=

tr

in

W

WTL log10

Critical

frequency

Effect of seals on windshield TL performance

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 45

Structural model

glass run

channel glass

incident

power

transmitted

power

air (I-FEM)

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 46

e

15

20

25

30

35

40

45

50

100 1000 10000

Fréquence (Hz)

TL

(d

B)

Epaisseur de 3.15 mm

Epaisseur de 3.50 mm

Epaisseur de 3.85 mm

Effect of glass thickness

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 47

3 lips

2 lips

15

20

25

30

35

40

45

50

100 1000 10000

Fréquence (Hz)

TL

(d

B)

Design 3 lèvres

Design 2 lèvres

Glass thickness of 3,85 mm

2-lips seal vs. 3-lips seal

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 48

Key Takeaways

➢ TBD

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 49

Chapter 18Sound transmissionJean-Louis Migeot

1. Sound transmission and insulation: definitions and measurement techniques

2. Low frequency model: rigid panel on elastic support

3. High frequency model: mass law and coincidence

4. General model

5. Double walls

6. Some comments

7. Application to a windshield