SOURCES AND EFFECTS OF LOW-FREQUENCY NOISE

The sources of human exposure to low-frequency noise and its effects a re reviewed. Low-frequency noise is common as background noise in urba n environments, and as an emission from many artificial sources: road vehicles, aircraft, industrial machinery, artillery and mining explosi ons, and air movement machinery including wind turbines, compressors, and ventilation or air-conditioning units. The effects of low-frequenc y noise are of particular concern because of its pervasiveness due to numerous sources, efficient propagation, and reduced efficacy of many structures (dwellings, walls, and hearing protection) in attenuating l ow-frequency noise compared with other noise. Intense low-frequency no ise appears to produce clear symptoms including respiratory impairment and aural pain. Although the effects of lower intensities of low-freq uency noise are difficult to establish for methodological reasons, evi dence suggests that a number of adverse effects of noise in general ar ise from exposure to low-frequency noise: Loudness judgments and annoy ance reactions are sometimes reported to be greater for low-frequency noise than other noises for equal sound-pressure level; annoyance is e xacerbated by rattle or vibration induced by low-frequency noise; spee ch intelligibility may be reduced more by low-frequency noise than oth er noises except those in the frequency range of speech itself, becaus e of the upward spread of masking. On the other hand, it is also possi ble that low-frequency noise provides some protection against the effe cts of simultaneous higher frequency noise on hearing. Research needs and policy decisions, based on what is currently known, are considered . (C) 1996 Acoustical Society of America.