Capsules vary not only in sensitivity (= output level for a given sound pressure level); they also vary in frequency response, particularly at both ends of the spectrum. You might not hear a 1 or 2 dB response deviation at 10 kHz in a mono recording--but if that same deviation occurs in just one microphone (and not the other one) of a pair that you're using for stereo, you're far more likely to hear and feel that something isn't right; our ears are much more sensitive in that situation, because our brains differentiate left vs. right amplitude and phase in an almost uncannily sensitive manner.
For people who record with X/Y or ORTF or Blumlein or other similar techniques, the more similar the two microphones are in all parameters, the better. So matched pairs are advantageous for that particular type of recording--which happens to be the kind that I think most people here do most of the time.
You can take a hint from the manufacturers of stereo microphones. The capsules are selected as matched pairs when the microphones are made, and if you damage a capsule on (say) a Neumann USM 69 and send it in for repair, the company will replace both capsules at the same time with a new, matched pair (a 15% additional fee is charged for the pair matching). If you buy a Schoeps MSTC 64 or CMXY 4V stereo microphone, you're getting a matched pair of capsules whether you like it or not; there's no option NOT to do so. AKG similarly used to pair-match the capsules in both their large-diaphragm and small-diaphragm stereo mikes. This is not just done for reasons of pride or looking good on paper; it directly affects the audible effectiveness of the microphone when used for precisely the purpose it was designed to be used for.
Most single microphones, however, are NOT sold to people who use them in coincident or closely-spaced pairs for stereo recording. Thus pair matching is unimportant to most customers. It's even considered a bad thing by some people, who feel that it reduces the chance of finding one really great (in their opinion) U 47 or C 12 that might occur in a batch. That's why most manufacturers haven't offered pair selection (which is a bit troublesome for them in a number of respects) to the general public until relatively recently--although well-connected customers have been offered it privately for at least as long as I've been in the business, or on an "if you know enough to ask for it, you can get it" basis, all of which I say from direct experience.
--A person could argue that pair selection is more important when the manufacturer is less strict about consistency to begin with; I wouldn't disagree. But then again, I wouldn't use any microphones for coincident or closely-spaced stereo setups unless they were very consistent to begin with. And it's very hard to make capsules be that consistent, even for the world's leading manufacturers. It's one of the major reasons why their microphones are expensive.
--best regards
Topic: Are match pairs really that critical (Read 5929 times)