Laboratory measurement of the acoustic absorption coefficient based on the modal dispersion

Abstract

This work presents a novel method of measurement of the absorption coefficient of large material samples in an acoustic waveguide in a broad frequency range. The material sample is deployed at one end of an acoustic waveguide the other end of which is excited with a point source. The sound pressure data are obtained using a long horizontal microphone array deployed in this waveguide. The optimization analysis is then applied to the sound pressure data to calculate the modal reflection coefficients, which are then combined to determine the overall absorption coefficient of the material sample placed at the end of this waveguide. It believed that this method will be able to extend significantly the frequency range attained with the current ISO 10543-2 impedance tube method and be applied to those materials which have a corrugated surface or complex surface morphology such as acoustic diffusers or living plants. It is also believed that this method will provide the means to estimate efficiently the diffusivity of materials with complex surface morphology with a relatively simple laboratory setup.