A design of array-microphone system using pressure-gradient microphones and two-dimensional finite impulse response filters

Abstract

Delay-and-sum array microphones consisting of a linear array of microphones can achieve sharp directivity at high frequencies. A disadvantage is that the directivity is frequencydependent. An array microphone using a fan filter is proposed to resolve that problem. However, it is necessary to increase the filter order to form a sharp beam at a low frequency. This paper is reported improvement of the array microphone directivity, realizing a narrow beam with a low order of the filter using a two-dimensional frequency domain design. Using four microphones, a second-order pressure-gradient microphone is formed. The spacing of the microphones is set for high sensitivity and broad bandwidth in the operating frequency range. These microphone units are placed along a line and are cascaded to a two-dimensional fan filter so that the load is distributed. In the proposed configuration, the second-order pressure-gradient microphone is cascaded with an axially symmetric fan filter. The configuration thereby forms a single broadside beam. Consequently, the directional characteristics of the pressure-gradient microphone are reflected in the array microphone and a sharp directivity, which is frequencyindependent, is obtained over a wide frequency range.