DETAILED ANALYSIS OF THE ACOUSTIC PROPERTIES OF A PERMEABLE MEMBRANE

A detailed analysis is carried out to clarify the mechanisms governing the acoustic performance of a permeable membrane and the effects of v arious material parameters. For this purpose, the theoretical solution s for the reflected and transmitted sound fields by an infinite permea ble membrane which have been derived in a previous paper(1) are approx imated to obtain simple expressions for normal incidence absorption an d transmission coefficients. An electrical circuit analogy is employed for a detailed analysis in which the particle velocity is separated i nto two components, i.e. the mass and the permeability, which is helpf ul in understanding their contributions to the acoustic properties of the permeable membrane. These considerations are aimed at demonstratin g the effects of the parameters on the acoustic properties as well as explaining the following particular phenomena which are observed in th e acoustic properties of a permeable membrane: the decrease of the sou nd energy absorbed in the structure al low frequencies and the increas e of transmission loss at low frequencies due to the permeability. The optimal value of flow resistance for the most effective absorption is also obtained from those solutions. (C) 1998 Elsevier Science Ltd. Al l rights reserved.