Microphone Placement 3 to 1 Rule

What is the 3 to 1 rule in microphone placement? Before I answer that, let me say a few things about what you should be trying to achieve as a sound engineer.  When making an audio recording, you want to make it sound good on multiple devices. Keep in mind that your recording could be played in the car, on an iphone, in a home movie theater, on a clock radio, and more. All of these are going to have a wide range of fidelity. Phase cancellation can really destroy a recording and make the playback sound poor on certain devices. We want to fix the problem at the source, and to do this we need good microphone placement.The 3 to 1 rule in microphone placement only applies when using multiple microphones and its simple rule to remember. To prevent phase cancellation, you should have 3 time the distance between microphones as what they are from their source. If have two mics, and the first mic is 1ft away from an acoustic guitar; the second mic should be at least 3ft away from the first mic. But if the second mic is 2ft away from its source, you should have 6ft distance separating the mics. Keeping this rule when setting up microphones will greatly reduce phase cancellation.

You will not always be able to keep 3 times the distance between microphones. Some mics are meant to be placed close together like stereo pairs. In the 3 to 1 rule, stereo pair mics should be counted as 1 mics. Stereo pairs a  set up with phase cancellation in mind. Its that phase cancellation and sound delay that help a persons brain determined what direction a sound is coming from.