Summary
Active Noise Control is a method for reducing noise while listening to other sounds.
Some active control devices are used in enclosed spaces such as ducts, vehicles cabins,
headphones and theaters but these are considered passive control noise control devices. The
active noise canceling is different from the passive canceling techniques because they include a
powered instrument rather than soundproofing techniques which do not require power.
How it works
Active Noise Control works by emitting a sound wave with the same amplitude as
the sound received. This new sound acts like a mirror of the original wave and is called the
antiphase. These waves are combined in what is called an interference and effectively cancel
out each other. Using this technique the unwanted noises are removed from the original sound.
Because the waves of sound that are best cancelled are those that have a constant frequency
and wavelength, this technique is widely used for environments with constant noises such as
plane engines or power generators.The devices used to create these sounds are called black
noise generators.
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In more modern techniques of sound control, a computer is used to match the wave
of the unwanted sound. Using this technique the interference created can target varying
wavelengths and frequencies.
Different types and applications
Applications of active noise canceling can be found in two categories, 1-dimensional
and 3-dimensional noise cancelling. 1-dimensional techniques requires two microphones and
a speakers. The most common use of this type of active noise canceling is on noise canceling
headphones which have receive a great customer attention in the past few years.
The other kind of active noise canceling requires the use of multiple microphones and
speakers. To obtain the best results, a listener has to stay in one position to and computers are
used to find the best canceling frequency. These techniques are less cost-effective than a 1-
dimensional approach so they are only used for professional work. Recently, car manufactures
have started adopting this technique because seats in a car cannot be rearranged making it
easier to target only certain positions of the car’s interior.
References
● http://en.wikipedia.org/wiki/Active_noise_control, 09/23/2010
● http://www.chrisruckman.com/ancfaq3.htm, 09/20/2010
● http://www.themotorreport.com.au/5928/toyota-to-fit-active-noise-cancelling-to-crown-
hybrid, 09/23/2010
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