ABSTRACT

The noise scale, decibels, confuses the general public because a doubling of the noise level gives an increase of only 3 dB. Noise control at lower levels is primarily to eliminate annoyance; noise control at levels of 90 dBA and up is to protect hearing. Conductive hearing loss occurs in the outer or middle ear from wax, punctured eardrum, or corrosion of the bones, among other causes. Often it can be cured with medical or surgical treatment. Nerve loss in the inner ear is rarely curable; it can be caused by old age, viruses, drugs, and noise. In addition to hearing, the ear provides a sense of balance through the pea-sized vestibular system, which is subdivided into the utricle and the semicircular canals. Hearing loss from noise can be temporary or permanent. Temporary threshold shift (TTS) is measured 2 minutes after the end of exposure. With repeated exposure, TTS becomes permanent threshold shift or noise-induced permanent threshold shift.