Active Noise Cancellation

Active noise cancellation is a technology that reduces background noise in enclosed spaces such as inside vehicles, noisy ducts, or busy offices. The most successful application of this technology is in noise-controlling headphones; pilots use them extensively. Lately, these headphones have dropped in price and have become popular for listening to CDs in noisy environments.

How Active Noise Cancellation Technology Works

It sounds like a made-up invention in a science fiction movie, but it works: headphones create anti-noise to cancel background sound. The headphones have tiny microphones that listen to incoming high-pressure sound waves and a fast amplifier that creates an opposite low-pressure sound wave. The waves cancel each other out and the background noise is reduced greatly.
While automobile and airplane manufacturers are working on incorporating active noise cancellation in the cabins of noisy vehicles, the most practical use has been in headphones. Helicopter pilots find them indispensable--they cut low-frequency propeller noise but still allow the wearer to hear mid- and high-frequency sounds, like voices and alarms. Please note: there is a difference between active and passive noise reduction headphones.

Active noise cancellation headphones work as mentioned: they create an opposite sound wave to negate noise. Passive cancellation doesn't cancel waves at all; instead, it blocks as much sound as possible (think thick earmuffs) and then filters loud sounds. The active noise reduction headphones are ideal for listening to music while traveling, while the passive variety are better for only blocking sounds, such as at a shooting range.