Estimation of surface impedance at oblique incidence based on sparse array processing

Abstract

A method is proposed to estimate the surface impedance of a large absorptive panel from free-field measurements with a spherical microphone array. The method relies on the reconstruction of the pressure and the particle velocity on the studied surface using an equivalent source method based on spherical array measurements. The sound field measured by the array is mainly composed of an incident and a reflected wave, so it can be represented as a spatially sparse problem. This makes it possible to use compressive sensing in order to enhance the resolution and the quality of the estimation. The results indicate an accurate reconstruction for angles of incidence between 0° and 60°, and between approximately 200 and 4000 Hz. Additionally, experimental challenges are discussed, such as the sample's finiteness at low frequencies and the estimation of the background noise.

Time domain room acoustic simulations using the spectral element method

“…(1), and in room acoustics it is natural to define the boundary conditions in terms of the complex, frequency dependent surface impedance Z(ω), which can be estimated from material models or from measurements. 45,46 The pressure and the particle velocity at the boundary are related through the surface impedance in the frequency domain viâ…”

The difficulties of simulating the acoustics of an empty rectangular room with an absorbing ceiling

“…The angle-dependent impedance is rarely available, because it can be prob-lematic to measure, especially for high angles of incidence and small samples [27,28]. It can therefore be necessary to use models for the estimation of it.…”

Additional Sound Absorption Within a Poroelastic Lamella Network Under Oblique Incidence

“…Temporal separation and acoustic field approaches can mainly be distinguished (see a review paper in [31]), the latter mostly having been applied following the transfer function method using two microphones, a sound source and different field assumptions (plane or spherical waves, with fixed [32] or rotating samples [22] in anechoic rooms). The first alternative approach of which mention can be made is the increasingly common use of spherical microphone arrays [33]. Another interesting method is that used by Tamura [34] who proposed a measurement procedure using the spatial Fourier transform for the decomposition of sound pressures measured in two planes above a sample into the incident and reflected sound pressures (with a fixed sound source).…”