SOUND FIELD OF A BAFFLED PISTON SOURCE COVERED BY A POROUS-MEDIUM LAYER

Two models for the prediction of sound transmission through a thick la yer of material which lies on a horizontal baffle are presented. These models are a preliminary investigation of a method for the acoustical and physical characterizations of porous materials. The acoustic sour ce is assumed to be a circular, baffled piston source mounted under a layer of porous material. The sound is transmitted through the porous layer to the semi-infinite half-space above the layer. The models are used to calculate the transfer function between the volume velocity of the source and the sound pressure above the porous material. The firs t model is based on the integral method in which appropriate Green's f unctions are used to describe the sound field, and on a collocation pr ocedure. The second model uses a method of decomposition of the sound field into cylindrical waves. The numerical results of the two models are in good agreement. A significant sensitivity of the transmitted so und field to the material's physical characteristics is observed. The models' predictions are in good agreement with those from the literatu re on the limiting case of a circular piston radiating in a semi-infin ite medium. The cylindrical wave decomposition method is found to be m uch faster in terms of computation time, and more general than the int egral method model. (C) 1995 Acoustical Society of America.