Indirect acoustical characterization of sound absorbing materials

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1 Indirect acoustical characterization of sound absorbing materials
Intro by Raymond Panneton Yacoubou Salissou Les présentateurs doivent souvent transmettre des informations techniques à des auditeurs qui connaissent moins bien le sujet et le vocabulaire spécifique. Les informations peuvent être multiples ou complexes. Pour présenter des informations techniques efficacement, utilisez les conseils suivants de Dale Carnegie Training®. Tenez compte du temps dont vous disposez et préparez la classification de vos informations. Délimitez votre sujet et découpez votre présentation en séquences claires. Suivez une progression logique et ne vous dispersez pas. Terminez la présentation par un résumé, un rappel des étapes clés ou une conclusion logique. Montrez l’intérêt que vous portez à votre assistance. Par exemple, utilisez toujours des données claires et pertinentes. Choisissez un niveau de détail et un vocabulaire adaptés à l'assistance. Utilisez des aides visuelles pour étayer vos points et étapes clés. Les auditeurs seront plus réceptifs si vous êtes à l'écoute de leurs besoins.

2 Sound absorbers Intro µ-Structure Types Granular, fiber, foam
Material Types Polymer, metal, textile, … Frame Types Elastic Acoustically rigid or limp Intro Modeling theories Biot theory (if frame is elastic) Equivalent fluid theory (else)

3 Equivalent fluid modeling
Rigid frame Helmholtz equation with equivalent density and bulk modulus Intro Limp frame Helmholtz equation with equivalent density and bulk modulus Total apparent mass of the bulk volume

4 Equivalent fluid modeling
Equivalent dynamic density Takes into account viscous and inertial effects Some recent models: Johnson et al. (1987) - , , ,  Pride et al. (1993) - , , , , 0 JL model JCA model Intro Equivalent dynamic bulk modulus Takes into account thermal effects Some recent models: Champoux and Allard (1991) - ,  Lafarge I (1993,1997) - , , k0 Lafarge II (1993) - , , k0, 0 Macroscopic parameters  - Open porosity  - Tortuosity  - Static airflow resistivity - Viscous characteristic length 0 - Static viscous tortuosity k0 - Static thermal permeability  - Thermal characteristic length 0 - Static thermal tortuosity

5 Equivalent fluid modeling
Equivalent dynamic density Intro Equivalent dynamic bulk modulus

6 Macroscopic parameters
Characterization Methods Direct Inversion Time Frequency Ultrasound Audio (impedance tube) Iterative Intro T.C.L. Tortuosity Resistivity Porosity Tortuosity Resistivity Porosity V.C.L. T.C.L. Tortuosity V.C.L. T.C.L. Tortuosity Resistivity Porosity V.C.L. T.C.L. Tortuosity Resistivity Porosity V.C.L. T.C.L. Ther. Perm. Number of searched parameters Number of searched parameters Accuracy Accuracy

7 Macroscopic parameters
Characterization Methods Direct Inversion Time Frequency Ultrasound Audio (impedance tube) Iterative Intro Porosity Tortuosity Resistivity V.C.L. T.C.L. Ther. Perm. Direct inversion

8 Direct inversion method
Main assumptions to verify Linear acoustics Sample is saturated by air at rest The open porosity of the sample is assumed known Sample is homogeneous (~symmetric) The frame of the sample is acoustically rigid or limp Sample has an Equivalent Fluid behavior which can be modeled accurately by the JCA model or the JL model Dynamic properties (eq, Keq) can be measured accurately Method

9 Direct inversion method
Analytical expressions for VISCOUS parameters From the Johnson et al. viscous model Method  f , Expected behaviors if sample follows model 9

10 Direct inversion method
Analytical expressions for THERMAL parameters From the Champoux-Allard thermal model From the Lafarge thermal model Method ’, ko’ f Expected behaviors if sample follows model 10

11 Measurements of eq and Keq
Some commonly used impedance tube methods Two-microphone/Two-cavity method by Utsono et al. Method Three-microphone method by Iwase et al. Four-microphone Transfer matrix by Song and Bolton. Modified three-microphone method Compared to 2-mic method: Not only surface meas. Compared to 3-mic Iwase method: no probe and standard Compared to 4-mic method: Uses less mics and transfer functions

12 Measurements of eq and Keq
L d Method ISO or ASTM E1050 for R and Zs

13 44.5 mm diameter impedance or transmission tube
Comparisons Melamine foam 44.5 mm diameter impedance or transmission tube Method

14 Description of sample Results Main properties Optional properties
Material: Polyurethane foam Diameter: mm (=tube diameter) Thickness: 50-mm Bulk density: 60 kg/m³ Open porosity:  0.005 Results Optional properties Static airflow resistivity:  250 Young’s modulus: ~ Pa

15 What we actually measure
Test 1 ok Frame Acoustical Excitability (FAE) What is done What we want to measure What we actually measure Acoustical measurements in the Standing Wave Tube (SWT) or Results or or Should reduce thickness! [see JASA 114(4) and JASA 116(1)]

16 Test 2 ok Through thickness symmetry (indication on homogeneity) Results 16 [see JASA 124(2)]

17 If limp then convert to rigid
Test 3 Rigid Observe eq and decide ! Rigid or limp? Rigid Results If limp then convert to rigid 17 [see JASA 122(6)]

18 Observe constancy of parameters !
Test 4 ok Equivalent fluid behavior following models Observe constancy of parameters !  f () Results 18

19 Results Results      =hf k0 =lf/8 lf Direct Inversion
Iterative Inversion Direct  - 0.960  0.005  2 609  387 2 400  125 2 300  250  1.28  0.01 1.29  0.01  202  14 211  20  =hf 376  28 360  36 k0 =lf/8 167  39 lf 373  38 Results 19

20 Results Results 20

21 Results Results 21

22 Concluding Remarks Conclusion

23 Thank you! Questions?