Sound propagation above a layer with a large refraction index

This study treats the solution of the wave field produced by a point source in the presence of a layered medium on an acoustically hard backing. It is shown that if the refraction index of the layer is sufficiently large, the solution may be brought back to the problem of propagation above a boundary of local reaction. The point impedance of the surface is expressed in terms of known functions by assuming that the layer is porous, which also makes it possible to obtain an approximate solution of high accuracy. Comparisons are made to similar approximate solutions by Ingard and Lawhead‐Rudnick. A new method of measuring the ground impedance as a function of frequency by estimating four constants is suggested. Finally, experiments are added, supporting the theory that the acoustical properties of ground could be physically described by some kind of porous layer and acoustically described by a point impedance. ’’Surface waves’’ are experimentally verified in terms of the suggested theory.