Microphone Directionality Considerations

Microphones pick up sound using different polar response patterns.

Important considerations when choosing a microphone’s polar response pattern include:

  1. Unidirectional microphones are less sensitive to off axis sound than omni directional types, hence pick up less ambient room sound.
  2. Unidirectional microphones are best used when a cleaner less reverberant sound is needed.
  3. Unidirectional microphones can be used at a greater distance than omni types and still achieve a high level of direct sound.
  4. It is important to appreciate that direct sound becomes weaker as it travels away from the sound source at a rate controlled by the inverse square law.
  5. Omni directional microphones pick up more room ambience than unidirectional types and should be placed closer to the sound source if intending to record direct sound.
  6. Unidirectional microphones are subjected to an increase in bass response the closer they are to a sound source. This phenomenon is known as the proximity effect.
  7. Ambient sound in a room is at nearly the same level throughout. This is because the sound has been reflected many times within the room until it is essentially non-directional. Reverberation is an example of non-directional sound.
  8. The ambient sound in a room becomes increasingly apparent as a microphone is placed further away from the direct sound source. If the microphone is placed beyond a certain distance from the sound source the ambient sound will begin to dominate the recording. The point which this happens is known as the critical distance.
  9. Unidirectional microphones are less prone to feedback than omnidirectional types. Feedback is the undesirable leakage of audio from loudspeakers back into a microphone, resulting in a loud squeal or howling sound.