Computation of radiation impedance of stepped piston radiator

A computer program was devised for applying the Helmholz integral formulation to determine the pressure distribution on the surface of a stepped piston radiator, which consists essentially of a series of frustrums of cones and sectors of plane circles. The same program can also be used for various axially symmetrical modes of vibration of the sphere and of the plane piston by suitably specifying the values of the input parameters that determine the shape of the surface and the angle between the normal to each surface element and its direction of vibration. Good agreement is obtained (usually < 1% error) with the known analytic solutions for these latter radiators for ka⩽ 2, using only ten node from pole to equator. The complex radiation impedance as a function of ka was computed for Lubell Laboratories model 98 underwater loudspeaker that vibrates by separating along its flexible equator. The results are compared with those of a sphere that vibrates likewise. [This work was supported by Lubell Laboratorie...