Earthworks TC40K Omni Mic

Originally published in the April 1997 issue of Recording Magazine, and

by Kevin Becka

The latest tiny diaphragm omnidirectional condenser mic is flat all the way up to 40 kHz–and it’s surprisingly good in lots of applications.

Earthworks Audio TC40KEarthworks Audio TC40K is the third model this young company has produced, following the discontinued OM-1 and the current TC30K. There are internal differences, but all three mics share the same unusual yet pleasing appearance: a brushed stainless steel body that tapers off to a less-than-pencil-thin business end. The TC30K goes for $500, the TC40K for $800.

The OM-1 boasted a nearly flat frequency response from 9 Hz to 30 kHz, but it worked only with electronically balanced inputs (Mackie, Tascam, Soundcraft etc.). The TC30K is the same mic (hence the 30K name), but it also works with mic preamps that use a transformer-coupled input. The TC40K, which also works with both types of preamps, is flat all the way up to 40 kHz (as its name implies). The mics can be bought as singles or as a matched pair for just double the price. The pairs are shipped in a beautiful cherry wood box and are matched very closely.

Why be supersonic?

"Why buy a mic that claims to be flat up to 40K if my hearing only covers a fraction of that range?" you ask, knowing that the textbook range of human hearing is 20 Hz to 20 kHz. For one, there’s research to indicate that we respond to those frequencies, even if we can’t hear them per se.

But Earthworks engineered their mic for the fastest impulse response which is the time it takes the diaphragm to come back to rest after encountering a wave; the extended frequency response is a byproduct of the fast impulse response. For perspective, the impulse settling time of a (large diaphragm) AKG 414 is about 350 microseconds (µsec), a B&K 4007 about 150 µsec, a TC30K 80 µsec, and the TC40K just 40 µsec. When the diaphragm returns to the rest position this quickly, it eliminates the inaccuracies and coloration that the mic itself introduces. With the quick return, the mic is ready to see another wave, so it can hear more of what’s really going on. This lets it capture more time domain information, which gives you more detail. Earthworks also used a smaller diaphragm. This in itself helps a lot, but it doesn’t come without a price: increased noise. While I like the TC30K enough to have bought a pair (favorite applications: drum overheads and acoustic guitar), my biggest complaint about them– as Earthworks readily admits–is their inevitable self-noise. But the TC40K is supposed to be quieter and flatter.

Studio tests

To check for lower noise, I ran a 30K and a 40K into two identical class A Calrec mic preamps, then on to two faders on the console (Neotek). The mic gain pot is detented on these preamps, making it easy to set both mics at the same level. Big surprise: the apparent noise level was pretty much identical. I ran the mics into two electronically balanced mic preamps on the console, with the same result: virtually no apparent difference in the noise level. Just to make sure I wasn’t hallucinating, I brought up a large diaphragm Audio-Technica 4050 mic on another channel to make sure it was quieter. It was (not to infer anything else–these are two very different mics).

Acoustic and electric guitars

I put up the two pairs of Earthworks mics in a spaced pair in front of a newly stringed acoustic guitar. One pair was pointing just above the sound hole where the neck meets the body, the other where the pick hits the strings (coming in from the tailpiece). You could hear clearly that the 40Ks were brighter and missing a lower mid boost that the 30Ks had. The 40K overtones were brighter, and overall the sound was more "in your face." The 40Ks outshone the 30Ks in this situation. Both mics exhibited an excellent stereo picture. We then brought out my Groove Tube Solo amp and put up a 30K, 40K, and a Shure SM57 in front of the cabinet. This is an odd choice, but the ’57 is a great mic in this situation so it makes sense to hear the difference. I tend to mix both a dynamic and condenser when miking a guitar cabinet.

In both clean and overdrive settings, the 40K again had more desirable qualities than the 30K. The ’57 showed more bite because it has that famous midrange presence boost, but it and the 40K made a nice combination.

Drum overheads

Side by side, with diaphragms a mic width away from each other, I put up two spaced pairs of 30Ks and 40Ks over a drum kit. I switched between sets in the control room as the drummer played cymbals and then the rest of the kit. The consensus was that the difference was too close to call. The 40Ks at times sounded like they had a little more top, but it was harder to pinpoint in this situation than on the guitar. The stereo image was equally good on both mics.

Again, I own a pair of 30Ks and really like them as drum overheads. They offer a great stereo image and require very little, if any, eq. The sound is like you’ve got your head right over the drummer. Live sound engineer Robert Scovill, a teaching colleague and email chum of mine, just got off the road mixing front of house for the Rush tour. He and drummer Neil Peart did a shootout of a number of mics and chose the TC30Ks as drum overheads for the tour. Enough said!

Lead vocals

Earthworks doesn’t recommend the TC40K for vocals. But we wanted to check it out anyway, so we set up a 30K, 40K, and an AT4050 behind a pop filter and in front of a vocalist. We compared the two Earthworks mics first, and surprisingly the 30K was the overall favorite. The same low mid bump that we didn’t like in the acoustic guitar test was beneficial here, the vocal sounded warmer. However, between lines, when the vocalist was taking a breath or the phrase ended, the noise factor was very apparent. This was especially audible when we brought up the AT4050 and compared it to both Earthworks mics. The noise would be a problem for me if I had to choose between these mics.


One might think that fixed omnis would be an esoteric and unusable choice for general applications. But their lack of proximity effect (so you can get very close to the source) and natural, uncolored sound makes them a real contender for any situation. I’ve always liked the Earthworks mics and use the TC30Ks every chance I get. The only surprise was that we were expecting the TC40K to be noticeably quieter than the TC30K. Still, weighing the price and sound, either of the Earthworks mics is a true bargain and I would highly recommend them for any mic locker, home or pro.

Kevin would like to thank Alicia Knox, Yuzuru Koyanagi and Larry Kuglin for the assistance and talent, and the Conservatory of Recording Arts & Sciences for the mics and facilities.

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