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I'm working on a project including usage of several smartphone built-in microphones. However, I have no idea what sensitivity (e.g. mV/Pa) should I expect. I haven't came across any manufacturer's specification that would reveal that info. And smartphones manuals never tell anything about microphones. Is there any way to find it apart from experiments?

chluchad
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3 Answers3

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Most phone mics have automatic gain control, active noise cancellation, and other processing which makes having a sensitivity spec somewhat useless.

Additionally you don't care about a mV/Pa spec since you do not have access to the analog signal anyway. You might want something like dbFS/Pa.

And to make matters worse, there is likely a wide variation from phone to phone. Even with phones of the same make and model. Phones are not known for having high quality microphones. It wouldn't surprise me to see a 6 dB variation between the same model of phone.

You'll have to do some experiments and measure the sensitivity. Even then, don't expect things to be good or consistent.

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    There's also the question of whether the phone is in speaker phone mode, or camera mode, or phone mode, which all can do different things to the input signal, even on the same phone. Between different brands and models... no standard. Frequency response (transfer function) also varies wildly. – Jon Watte Apr 27 '13 at 04:37
  • Can you expand a bit on the experiments one can do to measure the sensitivity? I guess comparing to a reference microphone in a quiet room/anechoic chamber? – gozzilli Sep 25 '15 at 16:02
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If you are tied to actual smartphone mics, David Kessner's answer is sadly accurate.

But if you have some freedom of choice you may simply be looking in the wrong place. A brief search for "microphone" on Farnell gave a dozen suggestions in the "semiconductor/special function" category (for MEMS mics) and making an arbitrary choice (OK a biased choice : I picked a Scottish company :-) gave me this datasheet.

Which shows 2 grades of mics : the standard

WM7120A - SNR 57dB, Sensitivity +/-3dB

fully justifies Dave's assertion of a 6dB spread in sensitivity but the premium

WM7120AE - SNR 57dB, Sensitivity +/-1dB

is picked for tighter tolerances (but probably costs more than £1.89 each!)

Sensitivity is specified as -42dBv at 94dB SPL (1 Pa) at 1 kHz, which gives you the information you were looking for. I'm sure it's not the only mic on that search with a datasheet.

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Knowles is a supplier microphones to several smartphones, hearing aids, headsets etc. Find their website here: http://www.knowles.com/search/

You can easily find the information your are looking for in the many datasheets on that site.

Be aware that some of the microphones used in smartphones today have digital output, so there is no "mV" to measure :-)

Rolf Ostergaard
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