Eight males (aged 22-27) with normal ears were exposured to (1) steady state noise (broad band noise, 90dB). (2) impact noise with the frequency of one time per two seconds (peak value 105dB with about 25msec B-duration and peak value 120dB with 25msec and about 100msec B-duration), and (3) a combination of steady state noise and impact noise.
(1) Impact noise alone with a peak value of 105dB produced no significant TTS growth for steady state noise or combined noise above both.
(2) TTS growth of combined noise with impact noise (peak value 120dB, B-duration about 25msec) and steady state noise were larger than that of steady state noise alone, and the difference was statistically significant.
(3) In the case of third impact noise (peak value 120dB, B-duration 100msec), the effect to hearing loss was showed in following order, impact noise alone, combined both, steady state noise.
