After writing What is Phase? last week, one of my readers emailed me, asking me to address the 3:1 rule of microphone placement. (Thanks Mike!)

What is the 3:1 Rule? According to the handy Sweetwater glossary,

…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!