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1. Don Romano (alt) (thor@noagendasocial.com)'s status on Tuesday, 16-Apr-2019 06:48:49 EDT Don Romano (alt)

   Interesting diagram from ST Microelectronics' tutorial for MEMS microphones. You get some pretty good MEMS microphones with a ~70 dB SNR (compare with ~80 dB for a Neumann U87) and a near-flat frequency response. Their problem is the Helmholtz resonance. It varies considerably from capsule to capsule, so if you wanted to flatten that with a filter, you'd need to calibrate each capsule. Why don't they reduce the cavity volume to move that resonance into the ultrasonic range?

   1. Don Romano (alt) (thor@noagendasocial.com)'s status on Tuesday, 16-Apr-2019 07:40:51 EDT Don Romano (alt)

      in reply to

      Upon further investigation, it seems that the Helmholtz resonance of MEMS microphones is affected by the diameter, length and material of the opening to that chamber.

      1. Don Romano (alt) (thor@noagendasocial.com)'s status on Tuesday, 16-Apr-2019 08:17:16 EDT Don Romano (alt)

         in reply to

         Paper on acoustical design for MEMS microphones:

         https://www.edn.com/Pdf/ViewPdf?contentItemId=4429422

         It looks to me like almost no matter what you do to the opening to the front chamber, you get a resonance somewhere in the 10-20 kHz area.