Noise exposure and auditory physiology

Abstract

The ear is an extremely sensitive detector of acoustic energy. Its dynamic range at 1 kHz is at least 120 dB, although some harmonic distortion occurs at 70 to 80 dB SPL. The range of sensitivity is from about 20 to 20 000 Hz, although sensitivity decreases on both sides of an 800–7000 Hz band. There is an absolute limit above which the ear is likely to suffer direct physical damage: rupture of the eardrum occurs at about 140–160 dB SPL and, more importantly, destruction of the sensory elements of the inner ear at about 140–150 dB SPL. Much below these levels, i.e., starting at about 80–90 dB SPL, the sensory elements are gradually worn out, where there is some reciprocal relationship between exposure level and duration. There are some built-in protective mechanisms, but their effectiveness at industrial noise levels is rather low. After a brief outline of the ear's anatomy, some examples of noise-damaged ear tissues obtained in experimental animals and/or accidentally found in man will be demonstrated. [Supported by several NIH grants.]