Appendix C

Human Reactions to Low Levels of Intruding Noise

A Study by Dr. Lex Brown
Associate professor, School of Australian Environmental Studies, Griffith University, Queensland

I have been asked to comment on human response to noise of the type that may be generated by swimming pool filters in residential environments.

Most detailed studies of human responses to noise involve stimuli of greater intensity than those of concern here but while experimental data is lacking, various observations from studies or response to higher noise levels (road traffic noise, aircraft noise, etc.) provide information which will be relevant at lower exposures.

Noise is a stressor. At levels lower than those which cause direct physiological effects like damage to hearing, noise contributes to stress by interference with specific human activities of communication, sleeping and mental tasks and simply by being unwanted and annoying component of the environment. At the lower levels generated by swimming pool filters, direct interference with communication will not occur and behavioral awakenings are unlikely, but it is the unwanted and annoying nature of the sound which can result in stress.

A note in the Harvard Medical School Health Letter (Vol 11(8), 1986) provides a clear summary of the potential for such low levels of noise to affect humans:

...Unwanted, uncontrollable, and unpredictable noise well below 85 decibels may have physiological effects. Your neighbor's stereo does not have to be loud to prevent you from falling asleep. The fact that you have no control over it and cannot turn it off may be sufficiently upsetting... When the source of the noise is particularly disliked, then the sound may be even more irritating than it would otherwise be.

A typical response to this sort of intrusive lower level noise is the complex of physiological responses known as stress or arousal. These reactions may take the form of a change in heart rate or rhythm, an increase in blood pressure, a temporary rise in the level of blood cholesterol, or excessive secretion of certain hormones. Stress reactions are more common, and usually more severe, when the unpleasant stimulus is combined with a sense that there is no getting away from it and nothing can be done about it.

The latter is particularly pertinent with respect to unwanted, long-term experience of a neighbor's swimming pool filter noise in one’s own home for considerable periods of a day.

At what levels of noise might one expect to find this type of annoyance reaction? There is no simple answer. Human response to all sensory stimuli is highly variable and response to noise is no exception. Experimental data on people’s response to noise in their own homes always show a wide spread of responses at any particular level of the stimulus. Studies show that at high levels of noise some individuals still report no annoyance; at low levels of noise some individuals still report high annoyance.

However, what is observed is a shift in the median annoyance responses of a group of exposed people (half are more annoyed than the median response and the other half are less annoyed) from lower annoyance towards higher annoyance as noise levels increase. Thus response of a group is scientifically related to noise level but the response of any particular individual remains unpredictable. Various reasons have been proposed to account for this inter-personal variation - personality factors, history of exposure, adaptation, overall satisfaction with the neighborhood, attitude to noise source, different internal noise levels in the dwelling etc; but there is as yet no universal acceptance of any particular factor, or combination of factors. What is important is that all these responses are “normal” and as Bryan and Tempest (1973) point out with respect to responses to noise

....the concept of the “average” person is relatively meaningless.... There seems to be at least two types of person, one who “learns to live” with the noise, and gradually adapts to it, and another type who becomes progressively more disturbed by it, or it could be said is “sensitive to noise”.


....sensitivity to noise is a quite normal behavior pattern. There is a disturbing tendency to dismiss complaints by the noise-sensitive on the grounds that they not only complain about noise, but about other factors of their environment and are, therefore, “cranks” whose opinions can be justifiably ignored.

A useful conceptual model is that an inaudible noise for a particular receptor population will generate no annoyance (awareness of the existence of an unwanted noise source, even if inaudible, could conceivably generate stress in some). If that noise is audible then there is potential for some in a receptor population to be highly annoyed and as that noise becomes more and more prominent against other ambient sounds heard then one could expect a higher proportion of the receptor population to become annoyed. At levels which completely intrude, a majority would be annoyed.

The application of this model means that some annoyance reactions can be expected to an intruding noise as long as it remains audible. Audibility of a sound depends on its level and on its tonal components relative to the ambient sounds (more correctly, a sound is inaudible when it is masked by other sounds) but, in general, a sound is quite likely to be audible unless its levels are some 5 to 10 dB below the background level. This means that a noise from a swimming pool filter, even at levels below “5 dB above background”, can certainly be audible and have potential to generate annoyance reactions as described above.

In summary, there is nothing extraordinary or whimsical about a person becoming highly stressed by the presence, in their own home, of low level noise which is audible particularly where that noise is unwanted, uncontrollable, and for which their own home does not provide a refuge.

Bryan M.E. and Tempest W. (1973) Are our Noise laws adequate?
Applied Acoustics 6, 219-232
Dr. Lex Brown

Australian Environmental Studies, Griffith University, Nathan 4111, Queensland, Australia

Return to Swimming-pool Filter-motor Noise Pollution: Domestic Noise Pollution--An Australian Experience

Top of Appendix C
Appendix A: Case Histories
Appendix B: Memorandum of Advice
Appendix D: The “Solutions” Approach Versus the “Standards” Approach

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