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Reactions to low numbers of helicopter noise events (less than 50 per day) have been studied in a community setting utilizing a new type of study design. Community residents were repeatedly interviewed about daily noise annoyance reactions on days when helicopter noise exposures had, without the residents's knowledge, been controlled for study design purposes. The effects of maximum noise level and number of noise events on helicopter noise annoyance were found to be consistent with the principles contained in Leq-based noise indices. Although the best estimate of the effect of number of noise events is very nearly the same as that represented by the energy summation principle contained in Leq-based indices, the possibility that the number of noise events has only a small effect on annoyance cannot be rejected at the conventional p < 0.05 level. The effect of the duration of noise events was also found to be consistent with Leq-based indices. After removing the effect of differences in duration and noise levels, there is not an important difference between reactions to impulsive and nonimpulsive types of helicopters.

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