Damage‐Risk Criteria for Line Spectra

A series of experiments designed to elucidate the differences between pure tones and octave bands of noise in terms of their ability to arouse temporary threshold shift (TTS) is described. It is shown that the critical‐band concept is not relevant at high intensities, and that therefore the 10 dB correction factor currently employed, being based on the critical‐band concept, must usually be incorrect. Instead, it is demonstrated that the differences in TTS producing ability of tones and noises can be attributed mainly to their differences in ability to arouse the acoustic reflex; since noises cause more sustained contraction of the middle ear muscles than do pure tones, less TTS will usually be produced by noise. Because this difference in contraction, and hence in effective attenuation, is a variable function of frequency, intensity, and time, no one single decibel correction factor is appropriate. It is suggested that damage‐risk criteria for pure tones should be developed empirically by measuring TTS d...