Beamforming for a circular microphone array mounted on spherically shaped objects

This paper will discuss the concept of phase modes to generate a desired beam pattern for a circular microphone array mounted around a rigid sphere. The method will be described for arrays consisting of omnidirectional and dipole sensors. The sound diffraction caused by the sphere is taken into account. It will be seen that the method allows, with some restrictions, the design of a wide variety of broadband beam patterns for a given elevation which usually will be the plane of the array. The directivity index is used to characterize the three-dimensional behavior of the array. Simulations show the realization of different beam patterns, based on a 16-element circular array located at the equator of a sphere with radius 0.085 m. The frequency range of this array is from 300 Hz to 5 kHz. Especially at low frequencies, a very good combination of the directivity index and the white noise gain is achieved which cannot be realized with “conventional” beamforming for an array of similar dimensions. The simulations are verified by means of a measurement.