Three-to-one rule

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The 3: 1 rule (three-to-one rule) for microphone placement to minimize audible comb filter effects is as follows: If an instrument is a certain distance from a microphone , the next microphone that this instrument also picks up should be at least three times as long this distance from the first microphone.

The rule

The "three-to-one rule" for polymicrophone use

This is just a rough rule of thumb for the correct microphone placement, ignoring the fact that the instruments are played at different levels and that the microphones are directional microphones. Depending on the circumstances, this rule must therefore be flexibly adapted. The practical 3: 1 rule for the minimum distance from neighboring microphones for polymicrophones should always be followed when setting up the microphone. The smallest distance ratio of 3: 1 is assumed here, although the 4: 1 ratio and more is of course even more effective. It is idle to want to incorporate the directional characteristics of the microphones into this simple rule of thumb. This rule does not apply to classic recordings with main microphones and support microphones . The distance law applies to the calculations , in which the sound pressure at the microphone decreases with a distance of 1 / r from the sound source ; see the web link "Decrease in sound pressure - but correct".

particularities

Partial cancellation of certain frequency ranges (comb filter effect) can be heard when a sound source generates signal voltages of almost the same size for two microphones that are close together and these recorded signals are electrically interconnected, for example via the panpots . The reason is the phase delay difference that arises from the microphone distance to the sound source, with certain frequency ranges being raised by a maximum of (+) 6 dB in the overall level depending on the phase relationship , while others are in turn greatly reduced.

literature

  • Thomas Görne: Microphones in theory and practice. 8th edition, Elektor-Verlag, Aachen 2007, ISBN 978-3-89576-189-8
  • Norbert Pawera: Microphone Practice . 4th edition, Franzis Verlag GmbH, Munich 1993, ISBN 3-932275-54-3
  • Andreas Ederhof: The microphone book. 2nd edition, GC Carstensen Verlag, Munich 2006, ISBN 978-3-910098-35-0

Web links