Omnidirectional polar pattern: mic captures sound equally from all directions — ideal for room tone and ambience recording.
Technical Details
Omnidirectional microphones typically operate with a pressure transducer, where only one side of the diaphragm is exposed to sound pressure. The frequency response remains omnidirectionally stable up to approximately 10 kHz, beyond which the characteristic becomes increasingly directional. Condenser microphones achieve a frequency range of 20 Hz to 20 kHz with a sensitivity of -37 dBV/Pa. Dynamic omnidirectional microphones often exhibit a more limited frequency response from 50 Hz to 15 kHz, but higher robustness at a maximum sound pressure level of 134 dB SPL.
History & Development
The first practical omnidirectional microphone was developed by Western Electric in 1916 as a carbon microphone for telephony. Georg Neumann introduced the first tube condenser microphone, the CMV3, in 1928. The breakthrough came in 1962 with Neumann's U67, which offered switchable polar patterns for the first time. Modern digital signal processing has enabled omnidirectional condenser microphones with extremely linear frequency response and low self-noise of 7 dB-A since the 2000s.
Practical Use in Film
Omnidirectional microphones are used as ambient microphones for ambience recordings and as fill microphones in multi-track setups. In "Apocalypse Now" (1979), Walter Murch used omnidirectional microphones for the complex jungle atmospheres. In dialogue scenes, they are placed as hidden microphones in props, as their non-directional nature compensates for positioning errors. Disadvantages: higher susceptibility to feedback and poorer separation in multi-microphone setups compared to directional microphones.
Comparison & Alternatives
Unlike the cardioid with its heart-shaped polar pattern or the shotgun with its extreme directionality, the omnidirectional microphone captures sound equally from 360°. Modern alternatives include adaptive microphone arrays that simulate various polar patterns via DSP. In stereophony, the omnidirectional microphone is used for AB stereo, while XY technique requires cardioid microphones. Lavalier microphones mostly use an omnidirectional polar pattern due to the unpredictable body movements of the speakers.