Beschreibung:
The application of an approximate equation to describe the propagation of sound from a point source above an impedance plane [e.g., C. F. Chien and W. W. Soroka, J. Sound Vib. 43, 9–20 (1975)] is discussed. In particular, the correct choice of a complex root is specified. This choice is made by ensuring that the sound pressure be a bounded and continuous function of the geometrical parameters and the surface impedance.