The Dipole Microphone

Abstract

A dipole microphone is defined as a microphone whose response is a function of the pressure difference between two distinct acoustic terminals. One application takes the form of a wearable, close-talking microphone in which only the acoustic dipole element need be located near the mouth of the wearer. The sound is conducted through small tubes and is applied to opposite sides of a diaphragm housed with the remainder of the microphone elements in a case attached to the head or body of the wearer. Such a microphone exhibits strong discrimination against ambient noise. Tube resonances are avoided by correct termination of the tubes at the dipole ends, and without intermediate damping. Expressions are developed for the acoustic pick-up characteristics of a dipole close to a small source; for the over-all frequency response of the microphone; and for the random energy efficiency of a dipole as compared with that of one of its poles. Measured and computed characteristics of an experimental microphone are given.