Active noise control Guide, Meaning , Facts, Information and Description
Active noise control (also known as noise cancellation or antinoise) is a method for preventing unwanted sound. Sound consists of vibrations in the air, which can be represented as a wave. If a speaker emits a sound whose wave has the same amplitude and the exact opposite phase to the original sound, the waves cancel out and the result is no sound at all. A computer analyses the waveform of the background aural or nonaural noise, then generates a similar waveform rotated 180° out of phase to cancel it out by interference. This waveform has identical or directly proportional amplitude than the waveform of the noise, but its phase is the opposite.This method differs from passive noise control methods (sound proofing) in that a powered system is involved, rather than unpowered methods such as insulation, sound-absorbing ceiling tiles or automobile mufflers.
The advantages of active noise control methods compared to passive ones are:
- they are more effective at low frequencies
- they are less bulky, something valuable on aircrafts
- they can be made to be selective, i.e. to block noise (e.g. from an engine) but not useful signals (e.g. voice).
Protection of a 1-dimension zone is easier and requires only a couple of microphones and speakers to be effective. Several commercial applications have been successful: noise-cancelling headphones, active mufflers, control of noise in air conditioning pipes.
Protection of a 3-dimension zone requires many microphones and speakers, making it less cost-effective. Commercial applications include the protection of aircraft cabins and car interiors.
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