Microphone Directionality Considerations
Microphones pick up sound using different polar response patterns.
Important considerations when choosing a microphone’s polar response pattern include:
- Unidirectional microphones are less sensitive to off axis sound than omni directional types, hence pick up less ambient room sound.
- Unidirectional microphones are best used when a cleaner less reverberant sound is needed.
- Unidirectional microphones can be used at a greater distance than omni types and still achieve a high level of direct sound.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.