The effects of intermittent (trapezoidal) noise on man

Eight healthy students were exposed to intermittent noise to evaluate the effects of traffic noise on man. The experimental noise exposure conditions were as follows: Exp. 1: Control. Exp. 2: Peak level, 80 dB(A); rise-decay time, 1 sec; duration, 3 sec; and duty cycle 8 sec (on fraction 25%). Exp. 3: Peak level, 75 dB (A); rise-decay time, 500 msec; duration, 4.5 sec; and duty cycle, 8 sec (on fraction 50%). In all experiments, the exposure time was 14 hr. Temporary threshold shift (TTS) growth was followed for 14 hr while saliva cortisol levels were measured for a 24-hr period. Although the coefficient of the regression line of TTS growth recorded in Exp. 1 or Exp. 3 was not statistically significant, the value in Exp. 2 was statistically significant. The circadian rhythm pattern of the saliva cortisol level (during a 24-hr period, mean of 8 examinees) was observed in the three experiments. Essentially, the early morning level of saliva cortisol was high, while the daytime level was relatively low.