2.9. Are all 'active headphones' the same?
Description
This article is from the Active Noise Control FAQ, by Dr. Chris Ruckman
2.9. Are all 'active headphones' the same?
No. Two types are often called "active," but only one actually uses noise cancellation. For the sake of discussion, let's call the two types "active headphones" and "amplified earmuffs".
Active headphones rely primarily on noise cancellation for low- frequency quieting. In some, the earmuffs themselves provide relatively little passive noise reduction. In others, the earmuffs provide as much passive reduction as possible, using noise cancellation to get even better performance at low frequencies. In any case, the unit includes a microphone *inside* each earcup to monitor the "error" -- the part of the signal that has not been cancelled by the speakers. A pilot's headset also includes a microphone boom to transmit the pilots voice, and an input jack to transmit communication signals into the earcups. The noise cancellation works best on tones or periodic noise like that from an aircraft propeller.
Amplified earmuffs are quite different, as they do not use noise cancellation at all. A heavy passive earmuff attenuates as much noise as possible. Microphones on the *outside* of the unit pick up sounds that would ordinarily be heard by the ears. These microphone signals are then filtered before being played by speakers inside the earcups. The most common filtering is to mute loud, impulsive sounds such as gunshots; amplified earmuffs are therefore becoming quite popular at weapons firing ranges. (Example: the popular Peltor Tactical 7-S retails for around US$130.)
Amplified earmuffs have also been suggested for use by sufferers of tinnitus ("ringing of the ears"), a condition that can be aggravated by loud noises. But amplified earmuffs should not be confused with true active noise control headphones.
A new product has recently come to market: the Andrea Anti-Noise Computer Headset. This product includes an earpiece with a boom- mounted microphone, and is used to filter out background noise from voice signals recorded by the microphone. Details on this product will be included in a forthcoming posting; in the mean time, interested readers should contact Andrea directly and mention this FAQ. (Andrea Electronics Corporation, 11-40 45th Road, Long Island City, NY 11101, USA, phone 1.800.442.7787).
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