On Determining Smartphone Microphone Directivity with Application to Beamforming

Abstract

An equiangular sampling scheme and accessory measurement set-up for determining the directivity gain pattern of a commercially available smartphone is presented. Determining this directivity gain pattern based on these measuremenents was not possible, because next to the impulse response of the microphone also the impulse response of the acoustic system. Different smartphone set-ups are tested and the directivity of a smartphone on a surface differs from a smartphone in mid-air. The determined directivity gain pattern is suitable for use by a beamforming algorithm, but it resulted in no improvement of the performance of the algorithm. Interpolation of the measured results was not considered, as the system for which the measurements are intended cannot measure accurate smartphone orientations. Other work has shown that the orientation of a modern smartphone is not yet known within 10 degrees margins, therefore interpolation of the measured results is not considered. This could be included in future work, along with to the determination of indoor position of a smartphone, a sampling scheme with fewer samples and a means to reverse the contribution of the acoustic system to the measurements.