© 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
© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 15
Transmission coefficient
Normal velocity continuity:
Dynamic equations
© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 16
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
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
© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 21
Attenuation
Consider two identical fluids:
© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 22
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
© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 25
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
© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 35
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