Abstract:
Low-cost electret microphones are ubiquitous in telecommunications equipment. They are capable of providing nearly ideal response, while often employed as point receivers. However, uniform response is not always optimal, especially for digital applications or microphone arrays, nor is it easily achievable given mechanical packaging constraints. It is therefore essential for a given design to incorporate frequency-dependent effects of the microphone housing. Frequency shaping is typically done electrically, but acoustical filters can be realized by appropriate selection of series or parallel cavities at the microphone. Damping must be accounted for by estimating thermal-viscous effects of the cavity openings, or by introducing flow-resistive materials for which acoustical parameters are known or can be measured. The frequency effects of microphone housing geometries can be modeled using any one of several techniques, the choice dictated by the desired accuracy, complexity of the physical realization, and available resources. In this paper, two prediction methods will be discussed. First, classical lumped- and distributed-element models will be described along with analyses obtained using MATLAB. Second, some preliminary results of numerical models using boundary or finite element methods will be presented.