Analytical Modeling of Wave Interference Directional Microphones

Analytical models of a wave interference directional microphone were developed for use on a digital computer. Wave interference directional microphones consist of cylindrical tubes with sound pressure receiving ports spaced along their length. Electro-acoustical transducers are placed near one end. Both ends are terminated by acoustical impedance elements. The microphone is classified as an end-fire receiving array for air use. Variations of this type of microphone have existed for many years; however, a detailed analytical model was never developed and verified. The microphone was modeled using acoustical transmission line theory. The most important effects on performance, tests proved, are caused by internal sound wave propagation, and these effects can alter performance drastically from that predicted by geometric line array theory. The models were verified by comparison of measured and predicted frequency response and directivity of actual microphones.