There's more to microphones than MEMS

August 22, 2016 // By Bill Schweber
Bill Schweber considers conventional and MEMS microphones and draws parallels with CCD and CMOS image sensors.

The classical historical epitome of an analog transducer – the audio microphone – has largely become a MEMS-based component in recent years. According to a recent IHS report "Apple Products Are Driving Market Growth for MEMS Microphones," billions of these are now being shipped annually due to smartphone demand; the newest phones include multiple such devices for enhanced sound capture.

I generally place low credibility in market-research reports which predict the far-away future with meaningless high precision, such as one which claimed "75.4 Billion Devices Connected to the Internet of Things by 2025" (no, I am not making that up; I just don’t want to embarrass anyone here). However, I do have reasonable level of confidence in reports from credible sources that look at recent shipments or installations – they are usually good enough to allow meaningful discussion. The MEMS microphone report fits into the latter category.

I'm not sure if I should be excited or nostalgic about the MEMS microphone news. After all, the microphone is among the first widely used analog transducers. Microphone technologies and their electronic interfaces have been a major part of the analog world since the earliest days. Going way back, the basic carbon-granule version was one of the two key enablers for Bell’s telephone (the speaker was the other, of course).

That's why I was relieved when I saw a brief but fascinating article in the always-excellent Physics Today about pre-MEMS microphone technology. "The vocal microphone: Technology and practice" is a highly readable overview of how microphone development has influenced singers and their vocal techniques, an aspect of microphones about which I only knew a little (much of it wrong) with numerous misconceptions.

The article explained how different singing styles use and exploit the inherent characteristics of classic implementations such as carbon, ribbon, condenser, and moving-coil microphone designs. Although it didn’t go into interface circuitry, there is a lot of valuable design information available on line for each microphone type as well, much of it from analog component vendors.