tonedeaf, you wrote:
> I have a dumb question...when people run split omni's, do you run the capsules pointing forward or upward? I may have been messed up by seeing some Schoeps capsules, but I thought I saw someone once running some omni's with the capsules pointed towards the cieling??
John Willett's reply has the essential information in it, but jerryfreak also has a point: Sometimes it only looks as if a microphone is pointed upward (away from the main sound source).
The summary is that omnidirectional condenser microphones are generally pressure transducers, and if you want one with "flat frequency response" there are four basic design alternatives, which differ mainly in their behavior at high frequencies (say, 2 kHz and above):
(a) those which give flat response on axis, with reduced high-frequency response off axis;
(b) those which give flat response off axis, with elevated high-frequency response on axis;
(c) those which give flat response if you integrate all angles of sound incidence; and
(d) those which give flat response for all directions of sound incidence--literally the same frequency response on axis as off axis unlike (a), (b), or (c)--but are noisy.
Most people, given a choice, prefer some version of (c) for general music recording, except in special circumstances which call for (a) or (b). Few people prefer (d), but there are some such people, and there are also special circumstances in which their approach could make more sense than usual.
If you had (b)-type microphones, such as John Willett's KM 183Ds, then to use them at medium or close miking distances you would need to point them away from the main sound source to avoid the elevated high-frequency pickup which is characteristic of their type. The newer omni capsules which John mentioned are of type (a) and are very suitable for close, direct pickup without emphasizing the highs and without having to aim them away. In fact, if he aimed those mikes up at the ceiling, he'd get a sound that was deficient in the high frequencies.
On the other hand for distant pickup in a highly reverberant sound field, you really need something like a (b)-type microphone or else you'll notice the lack of highs right away. It's not exactly brightness or dullness since it's occurring mainly an octave or so higher than the range that determines ordinary brightness or dullness, but it's very noticeable when that range is out of balance with the rest of your sound pickup. An excess is more disturbing to most people (they hear it as "metallic" or "artificial" sounding) than a corresponding lack would be, but the lack is no fun, either.
For most music recording with omni mikes at moderate distances in moderately reverberant environments, an in-between response is usually preferred--but that type of microphone can't have flat frequency response on axis, unless it's so small that it would be unacceptably noisy. Instead it will have some moderate elevation (say 2 - 4 dB) at high frequencies on axis, rather than the 6 - 8 dB elevation of a (b)-type microphone.
--best regards
P.S.: For those desiring extra credit, acousticians would call (a) a "free-field" type of microphone and (b) a "diffuse-field" type. For recording in an anechoic chamber (a) is ideal, while for recording in a dreamspace where the echoes go on forever and there's no localizable direct sound, (b) is ideal.
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