An event-related analysis of awakening reactions due to nocturnal church bell noise.

The sleep disturbing effects of nocturnal ambient non-traffic related noises such as bell strokes emitted from church bell towers on nearby residents are presently unknown. Nonetheless, this specific noise source is suspected to cause sleep disturbances in a small but qualified minority of people living in the vicinity of the bell towers that throughout the night indicate the time with bell ringings. A field study was carried out to elucidate whether acoustic properties of such bell strokes relate to awakening and to provide event-related exposure-effect functions between acoustical predictors and awakening probability. Awakening reactions were determined in 27 voluntary subjects, measured in their home setting for four consecutive nights with ambulatory polysomnography (PSG) and concurrent acoustic recordings in- and outside the dwelling. Results indicate that the bell ringing events increase awakenings in a similar fashion as has previously been reported with transportation noise events and that awakening probability first and foremost depends on maximum sound pressure level of an event. The number of bell strokes and the personal variables gender, age, and noise sensitivity did not influence awakening probability significantly. Awakening probability by tendency increased with elapsed time after sleep onset, and was decreased during slow wave sleep and REM sleep compared to S2 sleep. The results suggest that a reduction of the maximum sound pressure level or an interruption of ringings during nighttime might reduce awakenings. The determined exposure-effect relationships are compared with similar functions for impulsive noise and transportation noise, more specifically, aircraft noise. The paper concludes with a few considerations regarding nighttime noise regulation.