Sidebar to the review of the TC30K. Reprinted by permission from the December 1996 issue of EQ
Every microphone has a characteristic "impulse response"--the manner in which it behaves after the sound source has stopped. Ideally, the diaphragm would cease moving as soon as the sound ended, but then there's that physics thing about bodies in motion wanting to stay in motion. Also, the diaphragm itself resonates, as do any cavities around the mic element, all of which contribute to the coloration and smear the arrival time of various frequencies. By using a very small, lightweight diaphragm housed in a body that has a minimum of resonance and reflective surfaces, coloration is reduced.
Earthworks microphone designer David Blackmer comments, "The human ear responds both to frequency and time relationships. Of the two--if you could say one is more important than the other--I think that time relationships are the most critical in determining what we hear and what qualities we assign to the sound. Every microphone sounds different, and even if you equalize them, they still won't sound the same. What I find is that the impulse response of the microphone and the quality you assign to it track each other very closely. Human hearing is capable of resolving time differences in the five to ten microsecond region, and so are our mics. You'll notice that the TC30K has a very simple shape and is not surrounded by any kind of cage because every cage has a complex acoustic signature. Since microseconds matter, every aspect of the shape is important. If we don't put the label on the mic, there is a 5/1000 inch groove and we can see an error near 1 kHz in the impulse response. It is very small, but it is there. We even had a customer say, 'Gee, the mic is a little funny around 1 kHz.' We told him to move the mic clip and the frequency response changed! So every detail--no matter how small--is important."
--Steve La Cerra