"Noise" is generally defined as unwanted sound and is perceived as a pollutant and an environmental stressor. As opposed to sound, noise involves a significant psychological component in addition to the physical component of sound perceived by the ear and transmitted by the auditory nerve to the temporal lobe in the brain.
Noise characteristics and levelsTypically, sound is described in terms of its intensity or sound pressure level, its frequency, periodicity, and duration. Sound pressure level is measured in decibels (dB). Since the human ear responds differently to different frequency ranges, filter meters that work more like the human ear are often used to measure sound pressure levels; in such cases, the unit is described as dBA, which means that a weighted filter was used.
Sound is also described in terms of equivalent sound levels (Leq), measurements that address average noise levels of fluctuating noises. Other characteristics, such as the predictability of the noise, its meaning, and the degree of personal control over noise, may influinfluence people's responses. The Table lists common noises and their sound levels.
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Table Typical noise levels |
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| Source | Decibels | ||||
Grand Canyon at night (birds, wind, no roads) Quiet room Typical living room Refrigerator Bathroom exhaust fan Normal conversation Clothes dryer Dishwasher Inside car, windows closed, 30 mph Urban street Hair dryer Vacuum cleaner Lawn mower Heavy truck (at 50 feet) Maximum output of stereo Construction site Jet takeoff (at 200 feet) |
10 28 - 33 40 40 - 43 54 - 55 55 - 65 56 - 58 63 - 66 68 - 73 80 80 - 95 84 - 89 88 - 94 90 100 - 110 110 120 |
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Adapted from Noise Pollution Clearinghouse |
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Exposure to environmental noise, including transport, construction, and industry noise, is increasing. While the intensity of noise from aircraft and cars may have diminished, the frequency of noise events seems to have increased in recent years, and the amount of the day without noise has lessened.1
General effects of noiseThere are several ways in which people's everyday functioning is disturbed by exposure to noise. The most widespread response to noise is annoyance; this includes elements of fear, mild anger, and a belief of being avoidably harmed.2 Reactions of annoyance are often associated with the degree of interference that noise causes in everyday activities. Dose-response relationships between the intensity of noise and annoyance from air, road, and rail transport have been found in a number of studies.3 Severe annoyance typically begins above 50 dBA to 55 dBA Leq.4
Exposure to noise during sleep has been related to difficulties in getting to sleep, changes in sleep stages, and awakenings.5 While effects of noise exposure on sleep are evident in laboratory studies, these effects are more difficult to demonstrate in community studies, where residents may habituate to prolonged noise exposure.6 There is no evidence that noise exposure, through insomnia, triggers depressive illness, although this pathway seems plausible.
There is also limited evidence of noise affecting pathophysiology, apart from the issue of noise-induced hearing loss. In occupational settings, for instance, there is evidence of raised levels of catecholamines and cortisol in persons exposed to very high levels of noise, typically above 80 dBA.7 Although the evidence is less convincing, there are some data that show hormonal responses in relation to environmental noise. There is also some evidence that aircraft and road traffic noise, typically at levels greater than 65 dBA to 70 dBA Leq, is related to a small increased risk of hypertension and coronary heart disease.8
