ACOUSTIC CHARACTERIZATION OF RIGID-FRAME AIR-FILLED POROUS-MEDIA USING BOTH REFLECTION AND TRANSMISSION MEASUREMENTS

Acoustic measurements in and above porous materials (500-mu m-diam gla ss beads) have been used to determine rigid-frame porous medium parame ters. The propagation constant for the acoustic signal propagating thr ough the air in the pores was calculated from probe microphone measure ments made inside the porous medium. Reflection measurements have been used to calculate the characteristic impedance of a thick porous medi um. A model relating porous medium properties to the propagation const ant and impedance was used to analyze the data from both the reflectio n and transmission measurements. Both reflection and transmission meas urements are needed to determine the rigid-frame porous medium paramet ers. Porous medium parameters can be calculated using the model and th e data. The calculated porous medium parameters from the transmission and reflection measurements are compared. Some possible explanations f or the discrepancy and suggestions for further work are presented. (C) 1996 Acoustical Society of America.