Abstract
Young male subjects were exposed to the following experimental conditions for 40 minutes, to clarify the effect on hearing of combined impact/steady-state noise.
(1) Exposure to a combination of 95dB steady-state noise and an impact noise of 121dB at the peak value and the time constant of 30m sec.: intervals between impacts were approximately 4sec. at a series of exposure and 250m sec. at the other.
(2) Exposure to a combination of 81dB steady-state noise and an impact noise 120dB at the peak value and the time constant of 10m sec.: intervals between peaks were approximately 1sec. at a series of exposure and 4sec. at the other.
Under the condition (1), the steady-state noise had a high sound pressure level (95dB); the test subjects' TTS growth at 4kHz was larger than at the exposure to only steady-state noise, but TTS growth at 1kHz was not so discernible. Under the condition (2), the steady-state noise had a comparatively low sound pressure level; the TTS growth at 4kHz as well as 1kHz was greater than at exposure to only steady-state noise. No noteworthy result was found concerning the relation between the change of “impact to impact” intervals and TTS values. These result indicate that impact noise at the condition of short “impact to impact” interval, and the steady-state noise with high sound pressure level invokes the acoustic reflex.
