Temporary threshold shifts produced by wideband noise

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Abstract
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 (TTS) 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.

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