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2:1 Rule of Ambience
To capture an equal amount of room ambience, a cardioid microphone must be placed twice as far from a source as an omnidirectional pattern microphone. Keep this in mind the next time you are trying to capture some of a room's natural sound when recording!

3:1 Rule of Microphone Placement
Yesterday we discussed the 2:1 Rule of Ambience. Today let's go one better with the 3:1 Rule of Mic Placement. When using two microphones to record a source, normally you will get the best results by placing the second mic three times the distance from the first mic that the first mic is from the source. Confusing? An example: If the first mic is 1 foot from a source, the second mic should be placed 3 feet from the second mic. Using the 3:1 Rule will minimize phase problems created by the time delay between mics.This rule originated when engineers were micing multiple sources in the same vicinity. The same principle applies. If you are recording two different sources of sound, their respective microphones should be at least three times further apart than they are close to their respective sources. Keep in mind that rules are meant to be broken; you may prefer the sound created by ignoring the 3:1 Rule - experiment and let your ears be your guide!

Blumlein Microphone (or Blumlein Pair)
Named for Alan Blumlein (chief engineer at EMI in London during the 1930's, and a pioneer in stereo audio), a Blumlein pair uses two coincident bi-directional (or figure 8) pattern microphones set up at 90 degrees to each other. This stereo miking technique provides a strong center image, and good room ambience. When using this technique, absolute polarity in the entire audio system is essential, mic distance from the source is critical in balancing ambience with direct sound, and since so much ambience is captured, a good sounding room is critical.

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