THE 
PRINCIPLE
One of the greatest stress factors nowadays is environmental noise. Investigations have revealed that noise affects the nervous system, causing e.g. weariness, lack of concentration, nervousness, and irritability. In addition, continuous noise exposure is potentially ear- damaging.
This problem concerns pilots in particular. Cockpit noise amounts to about 80 dB (A) in jets and to 90 up to 97 dB (A) in turboprops. During takeoff and landing, the noise level is even higher. To be able to understand radio traffic in spite of the noisy environment, the ATC signal level must be set to at least 95 dB (A). Permanent hearing loss caused by the continuous noise in aircrafts is the reason why many pilots became prematurely disabled and pilots lost their pilot´s license.
Circumaural communication headsets provide noise attenuating properties and are commonly used to address this problem. However, the noise attenuation of these headsets is uneven. High frequencies are reduced considerably, but low frequency wind and engine noise, the most prominent noise in many of today's aircrafts, is attenuated very little.
In response to these problems, Sennheiser electronic has developed an active noise compensation system which, combined with a
Active noise compensation is achieved by generating a signal identical in sound pressure level but exactly reversed in phase to the noise signal, the effect being that the
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