Estimation of locally reacting surface impedance at modal frequencies using an eigenvalue approximation technique.

Albert G Prinn,Emanuël A P Habets,Andreas Walther

doi:10.1121/10.0006742

Abstract

The accuracy of computational models for acoustics is often limited by a lack of reliable information concerning the frequency-dependent impedance of surface materials. This lack of information stems from the unavailability of reliable measurement methods for low frequencies. In this work, an approach is proposed, using eigenvalue analysis, for estimating the locally reacting, frequency-dependent impedance of a sound-absorbing sample. In particular, an eigenvalue approximation method is proposed and used in tandem with an optimization routine to obtain surface impedance estimates of an installed sample at modal frequencies. It is shown, using finite element simulations of an impedance tube and a small reverberation room, that the proposed method can provide reasonable estimates of the surface impedance of a sample placed on a boundary surface.

Highlights

Computational acoustic models often require reliable surface impedance information as input data
An eigenvalue approximation method is proposed and used in tandem with an optimization routine to obtain surface impedance estimates of an installed sample at modal frequencies. It is shown, using finite element simulations of an impedance tube and a small reverberation room, that the proposed method can provide reasonable estimates of the surface impedance of a sample placed on a boundary surface
This paper presents a method for estimating a sound-absorbing sample’s locally reacting, normal surface impedance at low frequencies

Summary

Introduction

Computational acoustic models often require reliable surface impedance information as input data. Using inaccurate data can lead to erroneous numerical solutions, as demonstrated in the work by Aretz and Vorl€ander.. Using inaccurate data can lead to erroneous numerical solutions, as demonstrated in the work by Aretz and Vorl€ander.1 This information can be difficult to obtain (see, for example, Aretz and Vorl€ander2), especially at low frequencies. An impedance tube can be used to measure the frequency-dependent, normal impedance of a small sample, whereas a reverberation chamber can be used to measure the frequency-dependent random incidence absorption coefficients of a large sample. These methods can be problematic at low frequencies and require dedicated measurement setups.

Methods

Discussion

Conclusion