There’s been some interesting discussion here about Micro-ElectroMechanical 
Systems (MEMS) microphones for ambisonic mic arrays. These devices seem to 
offer some compelling qualities (particularly small size and low cost) but 
their signal-to-noise spec is 65 dBA. Some folks posting here have seemed to 
suggest that this level of noise might possibly be acceptable.

IMHO, based on decades of experience, a microphone with a signal-to-noise ratio 
of 65 dBA is useless for professional recording. That's in the SNR range 
typical of consumer cassette tape machines or analog AM radio. 

For comparison, consider that professional large-diaphragm condenser mics 
achieve 120-130 dB SNR. The Sennheiser Ambeo has an SNR of about 110 dB. 
Portable digital audio recorders and popular audio interfaces make about 100 
dB, and Red Book CDs 98 dB. Even vinyl records are about 6 dB quieter than MEMS 
mic elements. 

Put a MEMS mic at the input of a digital recorder and you’re wasting 35 dB of 
dynamic range (not to mention the case of using several of them in an ambisonic 
array). That’s huge. A symphony orchestra playing at mezzoforte or louder may 
mask the noise if the mic is reasonably close to the stage, but forget trying 
to record softer passages. Recordists trying to capture natural ambiences will 
be sorely disappointed; a lot of what they’re trying to record will simply 
disappear into the noise floor. You might get away with using it for 
non-critical functions like background crowd noise for telecasts of sporting 
events, but that’s about it.

MEMS mics appear to me to have been developed for applications that require 
very small size, physical ruggedness, reasonable frequency response and low 
cost, but can tolerate a high noise floor. There are lots of such use cases, 
but professional audio is not one of them. If we wish to advance the art of 
ambisonic recording and reproduction, we cannot compromise basic performance 
specifications for the sake of a trendy idea.

Ralph Jones
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