THE SOUND FIELD WITHIN A RIGID POROUS LAYER

The sound field within a layered porous granular medium may be explore d by means of suitably protected probe microphones. The field within a system consisting of a granular surface layer above a thick porous su bstrate with considerably higher flow resistivity is modelled by assum ing the granular media to be characterized by uniform slit-pores withi n a rigid solid matrix and by applying boundary conditions at each int erface. The predicted relative amplitude spectrum within the surface l ayer is influenced by interferences between the first few wave compone nts of the internally reflected field. Predictions are in qualitative agreement with data obtained in washed sand and gravel.