Low Frequency Noise. What we know, what we do not know, and what we would like to know

Abstract

The paper reviews perception of low frequency noise (LFN) and the responses of people to LFN. Sometimes, when there are complaints of LFN and its effects, a specific noise cannot be measured. The possibilities are considered for development of enhanced sensitivity, for alternative (non-aural) receptors at very low frequencies and for false perceptions. The way in which we measure LFN may contribute to the problems. INTRODUCTIONThere is considerable misunderstanding about low frequency noise and infrasound Some of this is due to misleading presentations by scientists 30 or 40 years ago (Gavreau, 1968;Gavreau et al., 1966), which were interpreted selectively by the media in order to give eye-catching news stories. A succession of "reinterpretations" over a period of five or six years led infrasound and low frequency noise to be described in popular texts as a cause of death, whilst also possessing the ability to knock down buildings. (Watson, 1974). This aura of mystery and danger still persists today, deep in the minds of many people, where it waits for a trigger to bring it to the surface. The most recent trigger has been wind turbines.Although we know a great deal about low frequency noise, there are aspects which we cannot yet explain. We know about how people hear low frequency noise and that some have a low tolerance to it. We believe that low frequency noise may, in general, be more annoying than higher frequency noise, but do not know why this is so. We do not know why some people complain of a low frequency noise which cannot be measured separately from the background noise.It is also possible that there are subtle effects of low frequency noise on the body, which we do not yet understand.

‘Wind turbine syndrome’: fact or fiction?

“…12 This is for two reasons: firstly, the widespread use of A-weighting in sound measurement; and secondly, technical issues in the actual measurement process.…”

“…12 Regulations regarding noise In contrast to ultrasound, there are no clear protection standards established for infrasound. 5 Infrasound and low frequency noise are not currently recognised as disease agents, and therefore there is no legislation regarding permissible exposure levels and dose-response relationships.…”

“…18 A number of other countries have agreed upper limits of 80 dBA at 20 Hz frequencies and 20-40 dBA at 100 Hz. 12 Wind turbines are a new source of community noise to which relatively few people have been exposed. As the number of wind turbines increases, with a corresponding increase in the number of people exposed, guidelines will be needed to indicate the maximum safe exposure to infrasound and low frequency noise.…”

“…Studies have shown a hearing threshold as low as 4 Hz can be measured in an acoustic chamber, and 1.5 Hz for earphone listening. 12 Infrasound, if presented at a high enough level, may indeed be audible. 8,13 To become audible, the sound pressure level for a 20 Hz sound needs to be approximately 75 dB, compared with 4 dB for a 1000 Hz sound.…”

“…8,13 Historically, infrasound and low frequency noise have attracted much adverse publicity mainly based on misunderstanding and media hype, with stories such as the worker who 'fell dead on the spot' and the ability of infrasound to 'knock down buildings'. 12,13 Wind turbine syndrome has reinvigorated these anxieties about possible adverse health effects of infrasound.…”