Laboratory of Acoustics and Laboratory of Building PhysicsKatholieke Universiteit Leuven

Celestijnenlaan 200DB-3001 Leuven, BELGIUMhttp://fys.kuleuven.be/atf

A comparison between the structure-borne sound generated by a low-frequency

vibrating plate mounted on a light-weight structure and on a heavy-weight structure

Pieter Schevenels, Lieven De Geetere, Nathalie Geebelen, Gerrit Vermeir, Bart Ingelaere

Inter-noise 2007, Istanbul29th of August 2007

A comparison between the structure-borne sound ...Pieter Schevenels et al.

2/13

Outline

1. Introduction2. Experimental setup3. Mobilities4. Predicted and measured sound pressure

levels5. Conclusions

Inter-noise 2007, Istanbul29th of August 2007

A comparison between the structure-borne sound ...Pieter Schevenels et al.

3/13

1. Introduction ...

• Background- Flow of power

• Injection from source into structure• Distribution over structure• Radiation from structure into room

- EN 12354-5 •

Installed power ...

Introduction – Experimental setup – Mobilities – Predicted and measured SPLs – Conclusions

, ,, ,, , 1010lg lg4refi

ij ij refref

Ws inst s ip as i

SD

AL L

SR , , ,, ,, 10l 1g 0lg

4i

iWs insn t i sar

j refre

ief

fis j

SL

AS

DL R

Inter-noise 2007, Istanbul29th of August 2007

A comparison between the structure-borne sound ...Pieter Schevenels et al.

4/13

... Introduction ...

• Background- Installed power (1D, single contact point)

•

– Measuring F ...– Only in situ ...

•

– Source and receiver ...– Measuring vsf ...

• Reception plate method

– (force source assumption)

–

*12

W F v Source or receiver

Equivalent velocity source

Equivalent force source

2, ,2s rec rec rec rec x tW fm S v

2 2

2

1 12 2

isfi sb

s

YW v Y F

Y

21 12 sf

i

W vY

2

2

12

isf

s i

YW v

Y Y

Introduction – Experimental setup – Mobilities – Predicted and measured SPLs – Conclusions

, ,

Re

Rei

inst i s recrec

YW W

Y

Inter-noise 2007, Istanbul29th of August 2007

A comparison between the structure-borne sound ...Pieter Schevenels et al.

5/13

... Introduction

• Background- Installed power (1D, three contact points)

• Point mobilities Ykk and transfer mobilities Ykl

– Matrix formulation → lots of variables to measure

• Concept of effective mobilities– Incorporate all mobilities into one effective mobility YΣ

– Assumptions about forces in different contact points» Equal» Random phase

→

Introduction – Experimental setup – Mobilities – Predicted and measured SPLs – Conclusions

3

, ,1

1Re Re

3i k i kkk

Y Y

Inter-noise 2007, Istanbul29th of August 2007

A comparison between the structure-borne sound ...Pieter Schevenels et al.

6/13

2. Experimental setup ...

• Vibrating plate- 24, 40 and 60 Hz- Amplitude: 3 mm

• Reception plate- 2.0 x 2.8 m²- Thickness: 10 cm- Resiliently mounted

Introduction – Experimental setup – Mobilities – Predicted and measured SPLs – Conclusions

Inter-noise 2007, Istanbul29th of August 2007

A comparison between the structure-borne sound ...Pieter Schevenels et al.

7/13

... Experimental setup ...

• Floor plates (resiliently mounted)- Wooden floor (3.0 x 3.0 m²)

• Thickness: 25 cm– Fibreboard– 7 wooden joists with glass wool– 2 gypsum board plates

- Concrete floor (2.0 x 2.0 m²)• Thickness: 10 cm

- Floating floor (1.5 x 1.5 m²)• Thickness: 10 + 3 + 5 cm

– Mineral wool layer– Light-density concrete plate

Introduction – Experimental setup – Mobilities – Predicted and measured SPLs – Conclusions

Inter-noise 2007, Istanbul29th of August 2007

A comparison between the structure-borne sound ...Pieter Schevenels et al.

8/13

... Experimental setup

• Necessary data to predict SPL in lower room- Source characteristics

• Airborne sound power level LWa

• Structure-borne sound power level LWsn into reception plate

- Plate characteristics• Mobility Y• Internal loss factor η• Airborne sound insulation R

- Room characteristics• Reverberation time T• Volume V

Introduction – Experimental setup – Mobilities – Predicted and measured SPLs – Conclusions

Inter-noise 2007, Istanbul29th of August 2007

A comparison between the structure-borne sound ...Pieter Schevenels et al.

9/13

3. MobilitiesIntroduction – Experimental setup – Mobilities – Predicted and measured SPLs – Conclusions

63 125 250 500 1000 200010

-7

10-6

10-5

10-4

10-3

Frequency [Hz]Ave

rage

rea

l par

t of

eff

ectiv

e re

ceiv

er m

obili

ty [

m/N

s]

Wooden floorConcrete floorFloating floorReception plate

3

, ,1

1Re Re

3i k i kkk

Y Y

Inter-noise 2007, Istanbul29th of August 2007

A comparison between the structure-borne sound ...Pieter Schevenels et al.

10/13

63 125 250 500 1000 20000

20

40

60

80

100

Frequency [Hz]

Lp [

dB

(L)]

(re

2 1

0-5

Pa

)

Predicted SPLMeasured SPL

4. Predicted and measured SPLs ...

• Wooden floor

Introduction – Experimental setup – Mobilities – Predicted and measured SPLs – Conclusions

→ Force source assumption invalid at high mobility

Operating frequency: 40 Hz

,Re i kY

Inter-noise 2007, Istanbul29th of August 2007

A comparison between the structure-borne sound ...Pieter Schevenels et al.

11/13

63 125 250 500 1000 20000

20

40

60

80

100

Frequency [Hz]

Lp [

dB

(L)]

(re

2 1

0-5

Pa

)

Predicted SPLMeasured SPL

... Predicted and measured SPLs ...

• Floating floor

→ Force source assumption valid at low mobility

Introduction – Experimental setup – Mobilities – Predicted and measured SPLs – Conclusions

Operating frequency: 40 Hz

,Re i kY

Inter-noise 2007, Istanbul29th of August 2007

A comparison between the structure-borne sound ...Pieter Schevenels et al.

12/13

63 125 250 500 1000 20000

20

40

60

80

100

Frequency [Hz]

Lp [

dB

(L)]

(re

2 1

0-5

Pa

)

Predicted SPLMeasured SPL

63 125 250 500 1000 20000

20

40

60

80

100

Frequency [Hz]

Lp [

dB

(L)]

(re

2 1

0-5

Pa

)

Predicted SPLMeasured SPL

63 125 250 500 1000 20000

20

40

60

80

100

Frequency [Hz]

Lp [

dB

(L)]

(re

2 1

0-5

Pa

)

Predicted SPLMeasured SPL

Operating frequency: 60 HzOperating frequency: 40 Hz

... Predicted and measured SPLs

• Concrete floor

→ FSA must be valid for all frequencies→ FSA seems to be dependent on operation frequency

Introduction – Experimental setup – Mobilities – Predicted and measured SPLs – Conclusions

Operating frequency: 24 Hz

,Re i kY

Inter-noise 2007, Istanbul29th of August 2007

A comparison between the structure-borne sound ...Pieter Schevenels et al.

13/13

5. Conclusions

• Reception plate method- Easy method- Fewer measurements- Relatively accurate predictions

• Force source assumption- Possibly still good predictions when Ys is low

- But bad predictions at all frequencies when operating frequency lies in a frequency band where Ys ≈ Yi

→ Black-box model of source invalid→ Reaction forces do influence source behaviour

Introduction – Experimental setup – Mobilities – Predicted and measured SPLs – Conclusions