Characterization of MEMS microphone sensitivity and phase distributions with applications in array processing

An array with MEMS microphones can distinguish individual noise sources in an environment through spatial filtering. Its effectiveness depends on the variations in microphone sensitivity and phase. Quantification of these variations is valuable, because it enables assessment and optimization of array performance. This is particularly important if the measurements are to be used for enforcement of noise regulations.Nominal microphone sensitivity and phase are manufacturer-specified, but the distribution (histogram) around these values is not. Hence, this work demonstrates a free-field comparison method for measuring these variations in a batch of arrays. We also provide the histograms at 1 kHz for a sample population of 8384 Knowles SPH0641LM4H-1 MEMS microphones (131 arrays of 64 microphones). The histograms follow t-distributions, resulting in 95% confidence intervals of ±0.39dB for sensitivity and ±0.82◦ for phase. Finally, we illustrate that delay-and-sum beamforming with these microphones results in a Gumbel-distributed gain with −0.13/+0.10dB 95% confidence interval.