Design of a wideband, constant beamwidth, array microphone for use in the near-field

Directional microphones have long been proposed for the removal of room reverberation. An array microphone would seem ideal for this purpose since theoretically it can be aimed anywhere within the room. However, microphone pattern beamwidth is related to wavelength and aperture size. For a fixed size aperture, as wavelength goes down so does beamwidth. The change in beamwidth over a decade change in wavelength would seem to be unacceptable for this application. We discuss the design of a constant beamwidth array microphone for the frequency range 300 Hz to 3000 Hz. Because the microphone to talker distance is assumed to be about 3 ft. while the array has a 9 ft. aperture, the microphone is optimized for near field. We also discuss the use of a nonlinear optimization program for choosing the array parameters.