[Protection for noise-induced hearing loss using active hearing protection systems].

Though noise induced hearing loss is no longer the most frequent occupational disease in the Federal Republic of Germany, the environmental pollution by the product "noise" in our technical and industrialized world has not been reduced. On the contrary, the situation is worsened by the rising influence of leisure noise. To avoid occupational hearing loss, the "Noise Injury Prevention Code" issued by the insurers would demand wearing personal ear protection, e.g. ear plugs, if ambient noise levels are above 85 dB(A). But there are working places in which such equipment would have precisely the adverse effect, because one of the reasons for possible damage to hearing is radio communication. In military aircraft cockpits for example noise exposure measurements showed ambient noise levels above 90 dB(A) during regular flight service nearly all the time. To be able to understand radio traffic in spite of the noisy environment, the headphone volume must be raised above the noise of the engines. The use of ear plugs can only be of limited value. Whereas pilots with normal hearing show only little impairment of speech intelligibility, those with noise-induced hearing losses show substantial impairment that varies in proportion to their hearing loss. Communication abilities may be drastically reduced which may compromise the reliability of radio traffic. To avoid compromising air security one has to demand a noise protection system which allows to reduce ambient noise levels without disturbing speech intelligibility in the inevitable radio communication. Nowadays active noise cancelling (ANC) systems by electronic compensation in different ways provide effective protection against noise induced hearing loss.(ABSTRACT TRUNCATED AT 250 WORDS)