What are the main Acoustic parameters of a MEMS microphones? How are they defined?

[nmagniez]

Posted on January 14, 2014 at 16:34

What are the main Acoustic parameters of a MEMS microphones? How are they defined?

[Alessandro MORCELLI]

Posted on January 20, 2014 at 19:15

The basic acoustic parameters of a MEMS microphone are the Sensitivity, SNR, Frequency response and the Acoustic overload point. They are respectively defined as follow:

• The sensitivity is the electrical signal at the microphone output to a given acoustic pressure as input. The reference of acoustic pressure is 1 Pa or 94 dBSPL@1kHz. The sound pressure level, expressed in decibel, dBSPL=20*Log(P/Po) where Po = 20μPa is the threshold of hearing. 20*Log(1Pa/20μPa) = 94 dBSPL

• The signal-to-noise ratio specifies the ratio between a given reference signal to the amount of residual noise at the microphone output. The reference signal is the standard signal at the microphone output when the sound pressure is 1Pa @ 1 kHz (microphone sensitivity). The noise signal (residual noise) is the microphone electrical output at silence

• The Acoustic overload point is the maximum audio signal is that which the microphone can generate without distortion. Actually, the specification allows up to 10% in terms of distortion at the acoustic overload point

• The frequency response of a microphone in terms of magnitude indicates the sensitivity variation across the audio band. This parameter also describes the deviation of the output signal from the reference 0 dB. Typically, the reference for this measurement is exactly the sensitivity of the microphone @ 0 dB = 94 dBSPL @ 1 kHz.

Alessandro