Temporary threshold shift following 24-hour noise exposure.

Nine men were exposed to 24 hours of continuous noise in a sound field. The noise was an octave band centered at 4 kHz at levels 80 and 85 dB. Hearing thresholds were measured monaurally at 11 test frequencies ranging from 250 to 10000 Hz before, during, and after exposure. Temporary threshold shift (TTS) reached maximum levels at 8 to 12 hours of exposure. Maximum TTS occurred at 4 and 6 kHz. Mean asymptomtic threshold shifts (ATS) resulting from the 80 dB exposure level were 9.3 dB for 4 kHz and 7.2 dB for 6 kHz. For the 85 dB noise level, these threshold shifts were 17.8 dB and 14.6 dB respectively. The increase in ATS with increase of noise level for these two frequencies could be fitted with a straight line having a slope of 1.6.