Noise Suppression, also known as Active noise control (ANC), noise cancellation, active noise reduction (ANR) or antinoise, is the common term of the methodology for reducing unwanted sound. A noise suppression device, usually a set of strategically placed feedback microphones and noise-cancelation speakers, emits a sound wave with the same amplitude but with inverted phase to the targeted noise. The results of combined sound waves will have greatly reduced amplitude.
The noise suppression device may be co-located with the sound source to be attenuated. Alternatively, it may be placed at the location where sound attenuation is wanted, such as the worker’s compartment or simply in the form of a headphone. The second arrangement requires a much lower power level for cancellation but is effective only for a limited area or a single user. The price of noise-cancelling headphones has greatly reduced recently and become a popular choice among frequent flyers and people work in noisy areas.
The advantages of active noise control methods compared to passive ones are that they are generally:
- More effective at low frequencies.
- Less bulky.
- Able to block noise selectively.