Phase velocity measurements of sound in granular media: a time-domain approach based on deconvolution

This study presents a novel method for measuring phase velocities of airborne sound in porous materials, focusing on granular media. Using a single-microphone setup within an extended impedance tube, a time-domain method based on spectral division deconvolution was developed to isolate and analyse transmitted sound waves. Granular materials, including various size fractions of recycled silica sand, were used to investigate the frequency-dependent speed of sound and associated phase velocities, addressing the need for efficient, scalable techniques for measuring high-transmission-loss media. Results revealed that phase velocities in granular materials are highly dependent on particle size, with smaller granules exhibiting higher high-frequency tortuosity limits. The measured sound absorption values aligned closely with predictions from the Johnson-Champoux-Allard-Lafarge (JCAL) model for larger granules, though deviations were observed for smaller fractions due to structure-borne resonances. The proposed method proves effective for measuring phase velocities in granular media, offering a streamlined alternative to traditional approaches. Future research could apply this technique to other granular media and refine it for a broader range of environmental conditions. The efficiency and scalability of this method make it a valuable tool for advancing acoustic studies of porous materials.