The Effect of Compression on Sound Absorption of Multi-layered Isotropic and Transversely Isotropic Porous Materials at Oblique Incidence

Mohsen Lotfi

Abstract

Porous materials which are effective in sound absorption in automobile and airplane industry areoften used under compression. This compression is associated with a reduction in thickness and theresulting changes in acoustical properties and non-acoustical parameters of the porous materials.Therefore, these acoustics changes should be taken into account when the behavior of these materialsis studied. So far, the studies on the effect of compression on sound absorption characteristics ofporous materials have been limited to the single layered treatment of porous materials. This study ismeant to examine the effect of compression of multi-layered porous materials on the acousticalbehavior of these materials. To this end, the compression received by each layer because of the totalcompression is estimated. Next, the critical compression parameter is introduced as the limitingcompression exerted to the multi-layered. Using the compression ratio of each layer, one candetermine the sound absorption by a multi-layered treatment of isotropic and transversely isotopicporous materials. In addition, the present study examines the effect of compression on the acousticalbehavior of multi-layered of porous materials with and without a layer of air. In this study, thetransfer matrix method is used to study the acoustic behavior of materials. Moreover, the resultsobtained by TMM were confirmed using an impedance tube.

Abstract

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