Temporary threshold shifts produced by wideband noise.

Groups of human subjects were exposed in a sound field to a wideband noise for 24 or for 8 h on consecutive days. The wideband noise was composed of octave bands centered at 0.5, 1, 2, and 4 kHz. For the 24-h exposure, temporary threshold shift (TSS) increased for about 8 h and then reached a plateau or asymptote. TTS's at asymptote (ATS) increased about 1.7 dB/dB increase in noise level above about 78 dBA. TTS produced by single-octave band exposures were used to predict the TTS produced by the wideband exposures. Predictions were based on the "Intensity Rule" [W. D. Ward, A. Glorig, and D. L. Sklar, "Temporary threshold shift from octave-band noise: Applications to DRC's," J. Acoust. Soc. Am. 31, 522-528 (1959)]. Predictions were acceptably accurate and the validity of the "Intensity Rule" for 24-h exposures or 8-h exposures is supported. There is a remarkable coincidence between the relation which describes ATS and noise level, and the relation which describes noise-induced permanent threshold shift (in industrial workers) and noise level. This coincidence and animal data are used to support the hypothesis that TTS grows to an asymptote rather than a plateau, and that TTS at asymptote (ATS) produced by a given sound is an upper bound on any permanent threshold shift that can be produced by that sound.