"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 levels
Typically, 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.
Typical noise levels
Grand Canyon at night (birds, wind, no roads)
Typical living room
Bathroom exhaust fan
Inside car, windows closed, 30 mph
Heavy truck (at 50 feet)
Maximum output of stereo
Jet takeoff (at 200 feet)
28 - 33
40 - 43
54 - 55
55 - 65
56 - 58
63 - 66
68 - 73
80 - 95
84 - 89
88 - 94
100 - 110
Adapted from Noise Pollution Clearinghouse
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 noise
There 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
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