[Temporary threshold shift from equal energy intermittent noises].
This report deals with temporary threshold shifts (TTSs) induced by intermittent white noise and continuous noise of equal energy. On-times of the six intermittent noises in their same duty cycle, which was fixed at 1 s, were 25, 50, 100, 200, 400 and 800 ms and the corresponding sound pressure levels of the noise were 114, 111, 108, 105, 102 and 99 dB, maintaining the total energy of the noise at an equal level. The sound pressure level of the continuous noise was 98 dB. Seven young students with normal hearing acuity were exposed to these 7 sounds for 40 min. TTSs at 3, 4 and 6 kHz were measured at the time of 10, 20 and 40 min after the onset. The results showed that significant differences were found among the TTSs from the sounds with different on-times and in particular that TTS increased with on-times above 100 ms or 200 ms. This fact suggests that the equal energy assumption may not hold in the prediction of TTS from intermittent noise. It is suggested that both the on-fraction rule and the unit-step-function method might be applicable to the prediction of TTS due to intermittent noise with bursts longer than 200 ms.
D000328:Adult; D001305:Auditory Fatigue; D004781:Environmental Exposure; D006801:Humans; D008297:Male; D009622:Noise / Q000009:adverse effects*