Joan Kalso (MI) suggests the following extracts are particularly pertinent. Joan reports: "Parts of this document explore the unique problems caused by low frequency noise, which is one of the types made by wind turbine generators; Here are relevant excerpts from this study."
In industrial areas, the noise usually stems from a wide variety of sources, many of which are of complex nature. Various types of machinery are involved and they represent artificial noises which are of concern because they may contain predominantly low or high frequencies as well as tonal components, they may be impulsive and also present unpleasant and disruptive temporal sound patterns.
Machinery that moves air are of special interest because it usually creates noise with a large component of low frequencies. Unlike noise containing mainly higher frequencies, low-frequency noise is less attenuated by walls or other structures and it can cross great distances with little energy loss due to atmospheric and ground attenuation.
In residential areas, noise may stem from mechanical devices (e.g., heat pumps and ventilation systems, traffic) as well as voices, music and other kinds of noises generated by neighbors (e.g., lawn movers, vivid parties, and other social activities). Due to low-frequency characteristics, noise from ventilation systems in residential buildings may cause considerable concern even at low and moderate sound pressure levels.
Planners need to know the likely effects on the noise pollution in a community of introducing a new noise source as well as increasing the level of an existing source (Diamond & Rice, 1987). There are a number of models to predict annoyance due to a combination of noise sources, such as models of energy summation, of source addition, of source difference, of response summation and response inhibition, and of the (subjectively) dominant source (e.g., Vos, 1992a). Policy makers, when considering applications for new developments, must take into account maximum levels, equivalent levels, frequency of occurrence, and operating time of the major noise sources.
In order to avoid negative effects on REM-sleep, the equivalent continuous sound pressure level during the sleeping period should not exceed 30-35 dB LAeq for continuous noise indoors. In the case of fluctuating noise, the maximum level is best correlated to sleep disturbances. For isolated exposures as low as 45 dB LAmax, awakenings, changes of sleep depth, etc., have been shown. An increasing number of exposures results in greater risk of adverse effects on sleep.
Special attention should be given to noise sources in an environment with a low background level, to environments where a combination of noise and vibrations are produced and to sources with low frequency components where disturbances may occur even though the sound pressure level is below 45 dB LAmax.
Measures to reduce sleep disturbances during the first part of the night are most effective. As a first attempt efforts should be made to reduce the maximum sound pressure level of noise events and the number of noise events before focusing on reducing the equivalent continuous sound level.
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18.104.22.168 Low frequency noise and vibration
Low frequency noise is common as background noise in urban environments and as an emission from many artificial sources: road vehicles, aircraft, industrial machinery, artillery and mining explosions, and air movement machinery including wind turbines, compressors, and indoor ventilation and air conditioning units (Tempest, 1976; Leventhall, 1988). The effects of low-frequency 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 low frequency noise compared with other noise (B. Berglund, Hassmén, & Job,1994).
Intense low frequency noise may produce clear symptoms including respiratory impairment and aural pain (von Gierke & C.W. Nixon, 1976; see also von Békèsy, 1960). Although the effects of lower intensities of low frequency noise are difficult to establish for methodological reasons, evidence suggests that a number of adverse effects of noise in general may be greater for low frequency noise than for the same noise energy in higher frequencies: loudness judgments and annoyance reactions are greater for low frequency noise than other noises for equal sound pressure level regardless of which weighting scheme is employed (Goldstein, 1994); annoyance is exacerbated by rattle or vibration induced by low frequency noise; speech intelligibility may be reduced more by low frequency noise than other noises (except those in the frequency range of speech itself because of the upward spread of masking) (Pickett, 1959; Loeb, 1986).