Comparison of Position Estimation Methods for the Rotating Equatorial Microphone

We present a prototype of a microphone that moves rapidly along the equator of a rigid spherical scatterer. Our prototype allows for up to 100 rotations per second. It will enable processing methods like beamforming or sound field decomposition that are conventionally performed using microphone arrays. Solutions that assume one or more moving microphones have already been proposed in the literature but have not been verified in practise. Most of these methods require precise knowledge of the instantaneous microphone position, for which no convenient practical solution exists. Recent advancements in microphone array processing enable employing simple microphone trajectories, and recent advancements in 3D printing, microcontrollers, and high-speed electric motors allow for the required control of the movement. This paper presents the design of our prototype and evaluates its performance. Of particular interest is the accuracy of the estimation of the microphone’s instantaneous position. This paper demonstrates that monitoring the passing time instants of a photodiode that is integrated into the rotating sphere provides the highest precision and robustness.