Measurements of the Total Acoustic Radiation Impedance of Rigid Pistons in an Array

Abstract

MEASUREMENTS have recently been made of the radiation impedance of sound projectors working in arrays. The projectors used each consist of a 45° Z-cut ammonium dihydrogen phosphate crystal cemented to a flint-glass piston. The projectors resonate near 18 kc./s. and have a square face of side a = 0.55 in., so that ka = 1.050 = 27πa/λ, where k is the propagation constant of the fluid load, water, and λ is the sound wave-length in water. The equivalent circuit of this simple sound projector is known so that from a measurement of the electrical admittance of any projector near resonance it is possible to deduce both the radiation resistance and reactance at the piston diaphragm. For these measurements the projectors were driven in parallel at 3 volts, and the resonant frequencies of the projectors in air differed by less than 0.2 per cent.