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1. Don Romano (alt) (thor@noagendasocial.com)'s status on Friday, 19-Apr-2019 17:26:37 EDT Don Romano (alt)

   Example frequency response of a MEMS microphonen — from the ST Microelectronics Tutorial for MEMS Microphones.

   The Helmholtz resonance of a MEMS microphone looks inconvenient at first glance, but in the microphone array design I'm working on, I'm using two MEMS capsules to create a cardioid pattern, and if you space them apart just right, and induce a phase delay equal to the wave propagation time between them, the first notch in the resulting comb filter will flatten the peak.

   1. Don Romano (alt) (thor@noagendasocial.com)'s status on Friday, 19-Apr-2019 18:04:45 EDT Don Romano (alt)

      in reply to

      You can't actually see the center frequency of the Helmholtz resonator in most MEMS microphone datasheets, but if you look at the datasheet for an ultrasonic one, you can see it. The approximate parameters look to be:

      f = 25kHz
      g = 15dB
      Q = f / 8 kHz = 3.125

      It seems to vary a lot, but it wouldn't surprise me If 25 kHz is what they generally aim at as a compromise. Bigger diaphragm and displacement means better sensitivity and max SPL but also larger cavity and thus lower Helmholtz resonance.