01/01/2025
#5 Specialty mics
Measurement mics are made to measure sound, not to record or amplify sounds for your enjoyment. They’re generally omni-directional condensers, and the makers of these mics often mount the mic element or capsule at the end of the narrowest tube possible, to minimize any acoustic effect of the mic body itself. They’re also made to have a very flat frequency response, both on- and off-axis.
These mics come in really handy to measure the output of loudspeakers and how the room that they’re in, like a studio control room, affects that sound. Of course, they’re used for many other things, like measuring noise levels or in loudspeaker design, but it’s that first one that recording engineers are most interested in. It’s why I’ve got a few of these mics, and I used them when I did the last acoustic remodel of my control room a few years back, both to help me figure out what I needed to do, and to gauge the effectiveness of what I’d done.
There’s nothing saying you can’t use a measurement mic to record a guitar or an oboe, though. And while I’ve never used a measurement mic to record music (yet), some do.
Hydrophones are microphones made for recording sound underwater. I’ve never actually seen one, or had any reason to use one, as it’s just not something I do, but there are people who use them. If you’re recording whale songs, you’re using a hydrophone to do it. Water is much denser than air, so sound travels very well in it. That whale might be a long way away!
I imagine some of the most sensitive hydrophones are used on navy submarines. There aren’t many (or any) windows on a military sub, so listening to your surroundings with a sensitive hydrophone is very important so you might know when someone is sneaking up on you.
Contact microphones. As the name implies, these things are designed to be placed directly on whatever you’re trying to pick up. In a very simple form, they are piezo-electric discs which produce a signal when they are vibrated. Years ago, before digital reverbs, I had a plate reverb, which used contact mics to pick up the “reverbed” signal from the plate. The ones that came with it quit working after a few years so I replaced them with some home-made contact mics I’d put together, which looked pretty much just like the one in the photo. Other than them falling off the plate when the double-sided tape I used to attach them failed, they sounded fine. Commercial contact mics are prettier, of course.
You can get contact mics that are optimized for particular instruments, and just like regular microphones, proper placement is important. Some of these contact mics sound really good, and they can be a real asset when playing live, as they’re much less prone to feedback than a conventional mic.
The last mic I’ll mention is the noise-canceling mic. A noise-canceling mic is really just an extreme uni-directional mic. They’re used by people in noisy environments, like airplane cockpits. They’re engineered so the ambient noise, which is all around the mic, is drastically reduced, while sound coming from just one direction, like from the pilot’s mouth, is picked up. It’s hard to make a mic like this “sound good”, but luckily, that’s not the point. Intelligibility is.
It’s entirely possible I’ve left out some obscure kind of microphone, but the ones I’ve talked about in this series are the main ones people use on a day-to-day basis (except maybe the hydrophones). It can be fun and /or frustrating in the studio to find the right mic for a particular sound source, and then spend the time to place it in just the right position to get the sound that you’re hearing in your head, but when it all comes together, it can be very rewarding.