In SOUNDSCAPE studies, a sound perceived or understood as not belonging or inappropriate to a given sound environment, and thereby a contributor to SOUND POLLUTION.


Although sounds that have been newly introduced to an area are often noticed and actively disliked (see SOUND PHOBIA), with time most intrusive sounds gradually become accepted by the majority of the populace. Such sounds alter the ACOUSTIC HORIZON of the area, and in some cases disrupt daily activity. The so-called JET PAUSE in homes and schools near airports when noisy aircraft fly over is an extreme result of such intrusions.

Once accepted, intrusive sounds often gradually increase in intensity, such as has been the case with traffic noise in this century. If the growth is slow enough, public habituation and toleration seem to prevent any effective counteraction. However, a rapid growth in noise has been shown to result in a predictable level of public protest; see COMMUNITY NOISE EQUIVALENT LEVEL, NOISE AND NUMBER INDEX.

The degree of toleration of intrusions depends on many factors. Previous noise exposure tends to increase toleration, as do attitudes that rationalize the necessity of the sound. The particular time of day or year when the sound occurs is important as well; a few intrusions late at night, at mealtimes or during times of relaxation and leisure may produce more annoyance than a constant flow of intrusive sound when people are fully occupied with other activities. This phenomenon is partially recognized in noise rating schemes that weight nighttime flights heavier than daytime ones (COMMUNITY NOISE EQUIVALENT LEVEL, COMPOSITE NOISE RATING, NOISE EXPOSURE FORECAST).

Other factors affecting the degree of toleration involve the relationship between the noise producer and the community, such as when employer/employee relations are involved (see NOISE CRITERION), when the noise producer occupies an important economic place in the community, or when the majority of the population are individually involved, as with traffic noise. The degree to which the public believes that reasonable abatement efforts are being made by those responsible or in authority will tend to increase their degree of toleration. Finally, the level of community organization and self-awareness, as well as the available means for lodging protest, affects the probability that individual or collective action will be taken.

Sound Example: Formula One racing cars recorded at the Molson Indy car race in downtown Vancouver with peak levels at 105 dB. Many residents of the city regard this sound as an intrusion.