Microphones: An abundance of options for capturing tones

Having just covered the topic of speaker construction (specifically as it relates to in-ear headphones), both in one of last month’s blog posts and one of the prior month’s teardowns, I thought now would as good a time as any to tackle the other end of the audio reproduction chain: the microphone(s) employed for initial sound capture. As some of you may have already noticed, I sometimes generically refer to both speakers and microphones as transducers, since they convert between sound wave energy and electrical energy. You can alternatively use a passive speaker as a dynamic microphone after all, although it wouldn’t be very sensitive or frequency range-encompassing. And I suppose you could also use a dynamic microphone as a speaker, for that matter, although it’d be awful easy to overdrive and destroy it!

In this writeup, I’ll be discussing microphones in terms of options for you to consider using in your next virtual work meetings and/or off-hours jam sessions; a follow-on post will discuss integrating them on-PCB in your next design (including the pros and cons of each architecture option). Although I’ve long dabbled in mics, recent personal relevance has led to knowledge advance. Long-time readers may recall that I’ve often hung out in the “taper” section at live concerts, using my set of Oktava MC-102 (aka, MK-012) small diaphragm condenser mics with interchangeable cardioid, hypercardioid and omnidirectional capsules (evaluating a mic’s pickup pattern option(s) against your usage requirements is a key selection criterion, by the way):

(The large diaphragm cardioid capsule shown here is not part of my personal collection.)

and my Audio-Technica AT825 stereo large diaphragm condenser microphone:

I’ve also long had a pair of odd-looking (IMHO) but functional Blue (now owned by Logitech) Snowball USB-interface condenser mics in inventory:

Also in long-term inventory is a set of three Nady SP-5 dynamic mics that I acquired on the cheap nearly two decades ago, when a friend expressed interest in having me record her and bandmates performing in my makeshift home studio. The recording session didn’t end up happening but the mics, stands and cables I purchased in preparation remain in my possession:

More recently, in response to the COVID lockdown and subsequent evaporated availability of affordable virtual-meeting equipment, I admittedly went on a bit of a binge, outfitting both myself and my fellow work-from-home wife in preparation for the pandemic’s then-unknown duration. I began with several then-still-inexpensive Chinese-brand condenser mics with varying interfaces (XLR and USB), as sets complete with pop filters and either arms or stands. Here’s one example, and here’s another; the others have since vanished from Amazon’s inventory:

As the pandemic began to lift and brand-name gear once again became available at sane prices, I upgraded us to Blue Yeti condenser mics, one blue and the other grey, with USB interfaces:

and then two Mackie EM-USB condenser mics, more compact than the Yetis, one black and the other limited-edition white (I’ll let you guess which one was intended for my wife):

More recently, taking advantage of an Amazon Warehouse discount promotion, I snagged a notable sonic upgrade, a Rode NT1000 condenser mic with XLR interface, which normally sells for ~$350. My precious prize cost me half that price:

One thing you may have already noticed is that, except for the long-ago acquired Nadys, all the mics I’ve gotten to date are condensers, an architecture disproportion that’s representative of the preponderance of gear currently being marketed to live streamers and work-from-home virtual meeting participants, not to mention studio singers. Here’s how one good summary-of-types article I found describes condenser microphones, specifically of the electret variety:

Electret condenser microphones (ECMs) operate on the principle that the diaphragm and backplate interact with each other when sound enters the microphone. Either the diaphragm or backplate is electrically charged/polarized to create a magnetic field, [and] the interaction within the field causes a change in capacitance, corresponding to the change in distance between the diaphragm and backplate. A JFET [editor note: or vacuum tube] within the microphone capsule acts as a pre-amplifier and changes the varying capacitance to varying voltage for use with another preamplifier or amplifier to boost the signal to a usable output.

Another thing you may have already noted is that, with the exception of the small diaphragm (and also long-ago acquired) Oktavas and AT825, all of the other condenser mics I’ve mentioned have been side-address large diaphragm arrangements. While side designs make some sense, specifically in conjunction with multi-capsule architectures that allow for bi-directional pickup (when an interviewer and interviewee are sitting side-by-side with the mic in-between them, for example), speaking into the side of a microphone has always felt a bit weird to me. Apparently, I’m not alone, judging from the graphics I often see in instruction manuals:

Also, while the comparatively high sensitivity of a condenser microphone is great for capturing a singer’s sibilance and other nuances, it’s overkill for someone like me droning away monotone in Zoom. In fact, that same sensitivity can be counterproductive in that it also leads to an increasing likelihood that any background noise will also get picked up and passed along to listeners. Not to mention the fact that condenser mics require a dedicated power source, either an integrated battery (as is optionally the case with the aforementioned Audio-Technica AT825) or DC phantom power coming from whatever gear is on the other end of the XLR cable.

So when I had the chance thanks to an even more recent Amazon Warehouse discount promotion to pick up a like-new normally-$99 Audio-Technica AT2040 XLR-interface dynamic microphone (which the manufacturer appropriately promotes for use specifically in podcasting and other similar settings) for just over $70, I jumped at the opportunity:

Here’s how the article I mentioned earlier describes dynamic mics which, like speakers, operate under the principle of electromagnetic induction:

A dynamic microphone operates on the same basic electrical principles as a speaker, but in reverse. Sound waves strike the diaphragm, causing the attached voice coil to move through a magnetic gap creating current flow as the magnetic lines are broken.

When I plugged the AT2040 into my audio interface and spoke into it for the first time, however, I realized I hadn’t read the article’s description thoroughly enough:

While more robust than condenser microphones [editor note: thereby explaining why they’re commonly used in live concert settings], dynamic microphones are often much less sensitive (producing less signal, or voltage with a given sound input) than condenser microphones.

While someone with a more booming voice than mine might be able to sustainably drive a dynamic mic to adequate output levels, my soft speech wasn’t up for the task, even if I cranked the audio interface’s preamp boost setting to the max (which would degrade SNR, of course)…that is, unless I shouted, which definitely wasn’t natural, not to mention unsustainable. That’s when I discovered I needed a “pre-pre-amplifier” (my wording), a widget which is also a requirement for similarly low output ribbon microphones:

A type of microphone that uses a thin aluminum, duraluminum or nanofilm of electrically conductive ribbon placed between the poles of a magnet to produce a voltage by electromagnetic induction.

Such devices sit in-between a dynamic or ribbon microphone’s output and the audio interface or other connected device’s microphone input, boosting the levels to condenser microphone equivalents. They’re therefore commonly referred to as in-line preamps; you’ll also sometimes see them called “activators”. The nifty thing about them is that they’re “fueled” by the same phantom power that would normally drive a condenser mic but won’t pass that DC on to the dynamic or ribbon mic, which doesn’t need it and could in fact be damaged by it. Popular activators can cost well over a hundred dollars; mine set me back less than $40 and works fine:

All this talk about output levels reminds me of the final topic I planned to discuss in this particular post: interfaces. Perhaps obviously, if you go with a USB-interface mic such as the aforementioned Blue Snowballs and Yetis or Mackie EM-USBs, the entirety of the necessary preamplification is handled by circuitry within the microphone itself, ahead of the A/D stage. And since the USB mic’s output is digital, it’s not possible to “overdrive” the device the mic is connected to, although you certainly can still drive it to full-digital levels, and for that matter, overdrive the precursor analog stages; such mics therefore often integrate boost level controls to comprehend loud voices, etc. But re. “the device the mic is connected to”, such mics are useful only in combination with close-proximity PCs; you won’t find them in recording studios.

“Beefy” mics with analog audio outputs typically employ XLR interfaces; 3-pin for mono mics and five-pin for stereo mics like my AT825. Theoretically, they could also use ¼” TS (tip-side) plugs, but the phantom power necessary for condenser mic use wouldn’t be supported, and audio interfaces also generally assume that anything plugged into them via TS connectors is a guitar or other music instrument that delivers line levels (which no mic output can achieve).

And what about the simpler lavalier, shotgun and other external mics used directly (without a preamp or mixer intermediary) with video cameras and smartphones? Here a TS or TRS plug is commonly employed, since it’s all that’s available (larger connectors are incompatible with the devices’ more diminutive form factors). The key issue to watch out for here is two-fold:

Does the microphone assume that the connected device is also supplying it with phantom power? Or does the mic have its own power source (an integrated “coin” or other dry cell battery, for example) and ignore any phantom power supplied by the connected device? Or more egregiously, could any phantom power supplied by the connected device potentially damage the microphone?
And does the microphone’s need-or-not for phantom power correlate to what the connected device is supplying (or not)?

I’d originally also planned to discuss microphone technology and architecture options for on-PCB design…but having crossed through 1,500 words already, I think it’s wise that I wrap up at this point and (as mentioned at the updated-before-submitting introduction to this piece) save “the rest of the story” for another time. What are some of your favorite microphones, and how many are in your inventory? “Sound off” in the comments!

Brian Dipert is the Editor-in-Chief of the Edge AI and Vision Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company’s online newsletter.

Related articles:

Earbud implementation options: Taking a test drive(r)
Apple’s Beats Powerbeats Pro: No repair…a teardown, though!
Noise-suppressing headsets and earbuds: Differences, but all telephony duds
Audio experts on microphone levels and pressure zone mics
How do noise-cancelling microphones work?
Basic principles of MEMS microphones
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