"One-point stereo microphones" with coincident cardioids were introduced around 1970 and were originally designed for use with cassette recorders. Most had response peaks to emphasize spoken consonants and a very wide arc of pickup (e.g. 180 degrees with each cardioid's axis aimed 45 degrees away from center).
The improvement over mono recording is huge when you're trying to transcribe conferences or meetings, as people interrupt each other and have side conversations. With stereo headphones, a little patience and maybe something to filter out the low frequency room rumble, you can recover an amazing amount of whatever was said even if the microphone position was less than ideal.
That application established this type of microphone in the marketplace. And when portable consumer video cameras were introduced some years later, and stereo sound was added as a high-end feature, one-point stereo microphones were the obvious choice there, too. But they really only worked in small rooms. If you tried to record little Jimmy's school play from the middle of the auditorium, the result would be swamped with room sound because the distance was too great and the pickup arc far too wide.
Unfortunately that problem applies to like us as well. In stereo music recording from an audience position, your usual microphone location is often as far from the sound sources as the farthest left and farthest right sound sources are from each other--like an equilateral triangle or an even narrower wedge. And coincident cardioids can't differentiate that finely because a cardioid pattern is a rather blunt instrument. So to use cardioids for distant or semi-distant stereo music pickup, some degree of spacing is really necessary. Otherwise you tend to get recordings with too much correlation between channels--too much like mono, especially at low frequencies.
Topic: placing stereo card mics too close together? (Read 1855 times)