Direction Pressure-Gradient Microphones for Low Frequencies

Abstract

Pressure-gradient microphones of first and higher orders formed by the differential output of pressure sensors can provide directivity at low frequencies in a small package. These directivity patterns are given by the relationship F(θ)=cosn θ, where n represents the order of the gradient. By the inclusion of time delays in the formation of the pressure gradient, uniaxial response and improved directional efficiency can be obtained. For the case of colinear sensors, an analysis is given for the determination of the time delays that give the maximum noise suppression under a uniformly distributed random-noise field. The effect of nonuniform response in the individual sensors has been studied and found to be critical for the lowest frequencies.