Acoustical characterization of rigid porous materials.

Abstract

In an earlier study [K. M. Li, J. Acoust. Soc. Am. Soc. 123, 1352–1363 (2008)], an analytical expression has been derived to predict the penetration of sound into a rigid porous ground due to a monopole source. In the present study, this analytical formula has been exploited for a numerical method to characterize the acoustical properties of rigid porous materials. They can be obtained from a pair of excess attenuation spectra measured above and below a thick layer of the material. Specifically, its propagation constant and complex density ratio can be determined from the measured data by a downhill simplex method. A series of preliminary indoor measurements was conducted in an anechoic chamber for measuring the propagation of sound above and below a layer of glass beads of different sizes. Based on the measured excess attenuation spectra, the acoustical characteristics of two different sizes of glass beads were determined numerically. These acoustical parameters were compared with the predictions based on the classical impedance model.