A simulation of condenser microphones in free field by boundary element approach

Abstract

A boundary element approach to simulate the characteristics of a microphone in free field is presented. To describe the approach, a condenser microphone is considered as a typical model. The usual boundary element technique is applied to the free acoustic field outside the microphone and a new special boundary element is developed to include the effect of a very thin air layer between the diaphragm and the backplate of the microphone. The vibration of the diaphragm is expressed in terms of its normal modes which are combined with the boundary elements to find the frequency response and the directivity. A numerical example is given for the condenser microphone used as the standard microphone in acoustical measurement, in which the diffraction from the preamplifier house and the nose cone is included. The computed results are in good comparison with the measured data in the operating frequency range.