A Robust Null-Steering Beamformer for Acoustic Feedback Cancellation for a Multi-Microphone Earpiece

Abstract:
To reduce acoustic feedback in hearing aids, adaptive filters are commonly used to estimate the feedback contribution in the microphone(s). While theoretically allowing for perfect feedback cancellation, in practice the solution is typically biased due to the closed-loop acoustical system. For an earpiece with multiple integrated microphones and loudspeakers, we propose to use a fixed beamformer to cancel the acoustic feedback. By steering a spatial null in the direction of the hearing aid loudspeaker we show that theoretically perfect feedback cancellation can be achieved. To increase the robustness, the null-steering beamformer is computed based on multiple measured acoustic feedback paths. Experimental results using an earpiece with two microphones in the vent and a third microphone in the concha show that the proposed robust null-steering beamformer substantially and robustly increases the added stable gain while maintaining a high perceptual quality.