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Analog Angle Blog

More to Microphones than MEMS

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 even 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 which 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.

Building an interface circuit for a microphone is a nice entry point into the broader world of analog circuitry, and a great starter project for an aspiring student. It’s a topic brewing with issues of circuitry, of course, as well as preamplifiers, providing DC (phantom) power through the audio cable, impedance issues, ground loops, isolation, and many other real-world considerations. For those students who are more interested in mechanical engineering rather than electronics, there are online features and videos on how to build various microphones. They are nice, non-trivial hands-on projects which can be tangibly demonstrated at a school science fair or maker-type event.

Will MEMS microphones supplant the classics? The article notes that the Shure 55 Unidyne has been in production since 1939. In some ways, the MEMS devices already have. I did some research and couldn't find any numbers on the number of non-MEMS microphones sold annually, but it is undoubtedly many orders of magnitude less than that of the MEMS devices used in smartphones. I'd like to think that the audio characteristics and unique attributes of the MEMS units will never come close to the best of the traditional designs.

The Shure 55 Unidyne microphone is more than just a well-known, widely recognized classic icon and image, it is still being manufactured and in widespread use, over 75 years after its introduction. (Photo: Shure Incorporated)

The Shure 55 Unidyne microphone is more than just a well-known, widely recognized classic icon and image, it is still being manufactured and in widespread use, over 75 years after its introduction. (Photo: Shure Incorporated)

But it's probably prudent to “never say never” when it comes to technology advances. It wasn't very long ago when we were assured that CCD-based imaging devices would not be replaced by CMOS imagers for a very, very long time, because the performance of the former was so much better (resolution, color rendition, low-light capability, streaking and blooming issues, and speed). Fast-forward just a few years to the present, and CMOS imagers have improved amazingly across all these parameters, leaving CCD units primarily for highly specialized applications; the image-capture quality of some of the latest smartphones is tangible proof of CMOS performance.

What's your experience with microphones and their electronics? Have you ever built interfaces, either as a personal or school project, or for commercial use? Have you switched from non-MEMS to MEMS-based microphones due to cost, size, or other considerations?

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8 comments on “More to Microphones than MEMS

  1. juiceworld
    August 15, 2016

    Thank for sharing this info with us.

  2. k7jeb
    August 17, 2016

    The article asks that question, and a quick look at the specs for MEMS devices makes a strong argument for a YES answer.  Frequency response and overload characteristics both seem far superior to both dynamic and condenser types.  All that is needed is a huge housing to fake-out the talent.

  3. r@exida
    August 26, 2016

    The current problem with MEMS mikes is at the other end of the loudness range: noise. The noise of a microphone is ultimately due to random air molecules striking the diaphragm (Brownian motion). In order to get a respectable signal/noise ratio for a studio microphone, you need a diaphragm of at least a square centimeter. We need a MEMS technology with a high enough yield to build an array with this kind of area to break into the recording microphone market.

  4. Thomas7
    October 20, 2016

    Super! Interesting thought, I really enjoyed reading.

  5. ted90
    October 21, 2016

    was looking for this information, add your site to your favorites!

  6. Thomas7
    October 24, 2016

    Great and informative post!

  7. 98210005
    November 10, 2016

    A very useful article. Thank you for your share

  8. 98210005
    November 10, 2016

    A very useful article. Thank you for your share

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