Listening Comparison
I recorded a symphonic band simultaneously with a spaced-omni technique and a near-coincident technique. For spaced omnis I used two ACO Pacific MK224PH measurement mics at 12 feet from the ensemble and 30 inches apart.

These phantom-powered units have extremely low noise, flat response from 20 Hz to 20 kHz, and an XLR output.

For near-coincident mics I used two Neumann KM-140 cardioid condensers in the N.O.S. configuration at 20 feet from the ensemble. I boosted 100 Hz by 6 dB on the KM-140s to make their low end match the omni pair.

To me at least, the spaced omni’s have a wider stereo stage and more envelopment. The equalized cardioids don’t sound quite as natural to me as the spaced omni’s, but they have sharper imaging. Feel free to draw your own conclusions.

Comparing The Four Techniques
Coincident pair:
• Uses two directional mics angled apart with grilles touching.
• Level differences between channels produce the stereo effect.
• Images are sharp.
• Stereo spread ranges from narrow to accurate. 
• Signals are mono compatible.

Figure 7: Crown SASS-P MKII stereo PZM microphone, top view. (click to enlarge)

Spaced pair:
• Uses two mics spaced a few feet apart, aiming straight ahead.
• Time differences between channels produce the stereo effect.
• Off-center images are diffuse. 
• Stereo spread tends to be exaggerated unless a third center mic is used, or unless spacing is under 2 to 3 feet.
• Provides a warm sense of ambience.
• Provides excellent low-frequency response if you use omni condensers.
• Tends not to be mono compatible, but this may not be audible.

Near-coincident pair:
• Uses two directional mics angled apart and spaced a few inches apart horizontally.
• Level and time differences between channels produce the stereo effect.
• Images are sharp.
• Stereo spread tends to be accurate.
• The hall sounds more spacious than with coincident methods.
• Tends not to be mono compatible.

Figure 8. Miking setup for listening comparisons. (click to enlarge)

Baffled omni pair:
• Uses two omni mics, usually ear-spaced, with a baffle between them.
• Level, time, and spectral differences produce the stereo effect.
• Images are sharp.
• Stereo spread tends to be accurate.
• Excellent low-frequency response.
• Good imaging with headphones.
• The hall sounds more spacious than with coincident methods.
• Stereo spread is not adjustable except by panning the two channels toward the center.
• More conspicuous than other methods.
• Tends not to be mono compatible, but this might not be audible.

AES and Syn Aud Con member Bruce Bartlett is a recording engineer, microphone engineer and audio journalist. His latest books are Practical Recording Techniques (5th Ed.) and Recording Music On Location.

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