Absorption measurement of acoustic materials using a spherical microphone array

Abstract

Standardized methods for the sound absorption measurement are restricted to normal or diffuse incidence. The capture of the sound field over a plane material sample using a spherical microphone array has already been proposed as a solution to measure surface impedance or sound absorption. However, the proposed solutions use either modal beamforming or a direct computation of the pressure on the sphere. In this presentation, a method which uses the spherical harmonics expansion to calculate the absorption using the spherical holography principle is proposed. It allows to measure the characteristics of the material without relying on an accurate definition of the sound scene such as the exact position of the source but only on the distance of the spherical microphone to the material. Simulation and experimental result of surface impedance and sound absorption will be presented as well as comparisons with another approach from the literature based on sparse array processing of spherical antenna.