Noise is said to be perceived unwanted, annoying sound. It has become an increasing problem and in 1974 was said to be increasing within communities at a rate of one decibel a year.

This section deals only with environmental noise, not that of the workplace or home. In the outdoor environment the noise of a rushing trout stream is hardly perceived, much less perceived as bad or annoying. There is talk of "voice pollution", accumulated, unwanted, annoying sounds. Noise (yelling) that saves a person from an accident is good, otherwise bad. Herein, a concept of management and control is attempted to be presented, one over sounds and their perception. Frequency, intensity, pitch, and duration all influence the concept of noise.

Background

Forest and area noises like that of a stream are background. Children noises, vehicles, and other things contribute to background sound levels. The louder background sound levels, the closer a noise source can be to a receiver and still remain indistinguishable (Dailey and Redman 1975). For a noise source to be completely muffled, its level should be reduced to 15 dB below the background. (In the forest, this background level is about 35 dB; in residential areas it is about 62 dB; in industrial areas about 80 dB.)

Managing annoying sounds is needed to improve the quality of life. Extreme sound levels can be harmful to hearing. Noise levels cause an increase in blood pressure (Peterson et al. 1981). They are a health hazard (Berland 1970). There is high public anxiety about it. They interfere with schooling, speech, sleep, relaxation and privacy. They influence property value. Noise has been associated with decreased egg laying in poultry and decreased reproduction in mink. Harassment of wildlife by snowmobiles may be noise related, but bald eagles continued to nest when logging was conducted within 500 yards of their nest (Mathisen 1968). Sudden noises (e.g., sonic boom (Shurcliff no date)) can cause swallows to take flight destroying nests.

Management can and has reduced sound levels and this plan presents ways by which further control may be gained. There are technical and real physical limits that will be pressed but economic and social limits need to be addressed first.

Regulations may reduce sound levels but the sound path is likely to stay the same. The width of the path, thus the total area affected by sound sources, will decrease.

To this point within this section we have, perhaps, been too general in using noise and sound. A distinction, if retained hereinafter, can probably be very helpful. Sound is an oscillation in pressure of the air medium or the superposition of such propagated oscillations. Thus it is a physical phenomenon. Noise is any undesired auditory sensation (Harrison 1974). Noise is sound with a human value attached. Sound must be perceived for it to be noise.

Factors Affecting Sounds

The following is a list of factors that affect sound (thus whether it may ever be perceived as noise). Precise values are attempted but many factors are related. Later we shall present information on annoyance. The factors presented here are of general interest, somewhat useful in local situations, but especially useful in a computer program when inputs descriptive of a proposed action are made. The computer program, CAP66, is available for such computations.

Distance - Doubling the distance from a sound source will reduce the sound pressure on a receiver by a factor of four. This is called spherical divergence. Losses are about 2 dB per mile of distance.

Atmospheric Conditions - A sound wave loses energy in heat radiation and conduction, air viscosity, and diffusion. The higher the humidity and the higher the temperature, the less will be the noise removal. On days of fog, drizzle, or falling light snow, sound is normally observed to carry farther than on a clear day.

Vegetation - Contrary to popular conception, forest trees with natural ground cover are not effective sound barriers (Harrison 1974). Perhaps 2 dB per 100 feet may be used to estimate sound attenuation in the forest (with maximums of 10 dB at low frequencies and 15 dB at high frequency sound sources).

Planting trees in a 50 feet band (Reethof et al. 1976) may attenuate much sound.

Connotations

Harrison (1974) said that the amount of annoyance that a forest visitor experiences from the intrusion of any sound is largely based on the connotation of that sound, and not on its level. Woods can effectively reduce only low-intensity auditory impacts between campsites. To reduce such annoyance, they must, therefore, be reduced to below 15 dB background.

The personality of the observer, audial ability, culture and experience, location (city or forest), and expectations are all part of the perception, not just the sound level or duration.

Mulligan et al. (1982) confirmed this in studies. Vegetation may be a good acoustic barrier but its greater significance may be that it alters human response to sound (Anderson et al. 1981; Mulligan et al. 1981).

Harrison (1975) suggested 20 dB may be "silence" and 45 dB assumed a maximum level for the forest, with more stringent requirements for wilderness than for picnic areas and vehicle camping.

The effects of the above need to be added to get a new result.

Rigid Barriers

Barriers such as rocks, outcrops, or hills can be used to reduce auditory impacts between campsites (Dailey and Redman 1975).

Still Water - lake water surface between campsites is a liability in reducing auditory impacts.

Wind - wind "blows" noise to receivers, attenuates it most for those up-wind.

Plans

Producer	Receiver

Analyses and management need to move along two paths. One is to evaluate and study the producers, studying the GIS cells in a map between the source and sensor and the places where noise is most likely to be heard if and when a listener is present. GIS can be used to analyze where the most noise blockages occur over the longrun from all sources.The other pathway is to study and work with receivers looking at any point from an area from which noise may be heard if it is present. (If at A will I hear a noise from B?)

Progress in noise management is planned in an assortment of areas among the following:

1. Influencing aircraft flight conditions (timing, take-off, paths, aircraft)
2. Requiring quiet auto engines
3. Restricting conventional power saw (1995) use
4. Using improved pick-up and delivery procedures (e.g., reducing stops, improving containers)
5. Establishing "quiet zones" (both time and area)
6. Shielding a noise source
7. Closing roads during select periods
8. Excluding certain "loud" vehicles
9. Reducing auto speed
10. Altering road surfaces
11. Altering tire design
12. Altering road and trail location
13. Modifying roadside cuts to deflect noise into the highway
14. Using structural sound barriers
15. Reshaping buildings
16. Requiring noise insulation in buildings
17. Using natural sound barriers
18. Require disclosure of noise problems in real estate transactions
19. Educating people to reduce sounds produced that annoy others
20. Regulating time and place of ORV use (See section on off-road vehicles)
21. Enforcing laws. There are laws to assist:
    • The Federal Aviation Act (49 U.S. Code 1301)
    • The Noise Control Act of 1972 (2/2 U.S. Code 4908)
    • The Quiet Communities Act of 1978 (42 U.S. Code 4913)
    • and many state and local laws
22. Monitoring noise levels, reporting change (improvement)
23. Projecting and reporting on likely future noise levels and actions needed to manage them (contact EPA's National Information Center for Quiet)
24. Erecting solid sound barriers, then planting vegetation to reduce further noises (Cook and Van Haverbeke 1976)
25. Planting trees and shrubs close to the noise source, rather than close to the protected area, for best results
26. Using taller varieties of trees which have dense foliage and relatively uniform vertical foliage distribution (or combinations of shorter shrubs and taller trees to give this effect). Where the use of tall trees is not possible, use combinations of shorter shrubs and tall grass or similar soft ground cover, as opposed to paving, crushed rock, or gravel surfaces.
27. Planting trees and shrubs as close together as practical, to form a continuous, dense barrier. The spacing should conform to established local practices for each species.
28. Using evergreens or deciduous varieties which retain their leaves throughout most of the year.
29. Placing vegetation belts for maximum noise reduction, the belt of trees and shrubs approximately twice as long as the distance from the noise source. For example, if the noise is 100 feet away, the belt of trees should be 200 feed long. The noise screen should extend equal distances on both sides of the noise source.
30. Reducing noise from high-speed car and truck traffic in rural areas by planting 65- to 100-foot-wide belts of trees and shrubs with the edge of the belt within 50 to 80 feet of the traffic. Center row trees should be at least 45 feet tall.
31. Reducing noise from moderate-speed car traffic in urban areas by planting 20- to 50-foot-wide belts of trees and shrubs, with the edge of the belt 20 to 50 feet from the center of the nearest traffic lane. Use shrubs 6 to 8 feet tall next to the traffic lane, with backup rows of trees 50 to 30 feet tall.
32. Seeking contracts with low costs and low noise (a "buy quiet contract".)
33. Planting 2 rows of vegetation (when structure is 25 yards from the roadway center), one of shrubs at road edge, another of dense trees behind the shrubs. One or both are to be evergreen (Cook and Van Haverbeke, 1976). a 10 dB reduction can be expected, usually to 62-67 dB (Van Haverbeke and Cook, 1974).
34. Building an earthen dike, masonry wall, or solid wooden fence (one that also screens noise source from view). Add landscaping. (When structure is less than 20 yards from the roadway center, use both structures and vegetation.)

No single approach will work. A changing mix of the above efforts in a cost-effective strategy is likely to cause great improvements. The proportionate change in the dB level (between present level and the desired level) per dollar is a useful criterion. The "desired level" is specific to the people of the station. It may be a default value such as 35 dB as forest background (Dailey and Redman, 1975) or a lower value may be selected as a target.

The following is a newsprint letter to then-new President Bush (2001)

Air Tour Overflight Restrictions

A key and important area on which the Park Service has focused a major effort is "soundscape management" and the restoration of "natural quiet" to the park system. The NPS defines natural quiet as "the natural ambient sound conditions found in the park." The NPS has also defined "natural quiet" as a resource rather than a value. The Park Service has used "natural quiet" as the basis for severely limiting public access to a number of national parks such as Isle Royale in Michigan, Biscayne in Florida, and all the units currently allowing snowmobiles or personal water craft.

Air tours of the national parks, most notably Grand Canyon, is another form of access being severely restricted by the NPS. In 1995, Special Federal Aviation Regulation 50-2 (SFAR 50-2) was issued, establishing minimum altitudes and flight-free zones of portions of the Grand Canyon. SFAR 50-2 was highly successful in reducing visitor complaints about noise from tour aircraft. Even though natural quiet was restored, President Clinton again directed the agencies to "restore" natural quiet in the Grand Canyon by 2008. Thus, on March 28, 2000, the FAA issued a new set of rules concerning overflights. These rules included the modification of the air tour routes, and expansion of Flight Free Zones, and a limitation of the total number of commercial air tours in the Flight Area. However, by implementing these regulations the air tour industry will be severely restricted and may not be able to provide this form of access to over 800,000 park visitors.

from James V. Hansen, committee chair, Member of Congress

Additional information is available on general aviation airport related noise.

see work on recreation effects on wildlife at www.montanatws.org

References

Anderson, L. M., B. E. Mulligan, and L. S. Goodman. 1981. Esthetics of sound in outdoor settings. P. 109-121 in Proc. Southeastern Rec. Research Conf.

Berland, T. 1970. The fight for quiet. New Jersey. pp 88-89.

Bragson, C. R. 1985? Noise pollution. The unquiet crisis. Univ. Pennsylvania Press, Philadelphia, PA 305pp.

Cook, D. I., and D. F. Van Haverbeke. 1976. Residential traffic noise control using tree-shrub-barrier combinations. P. 112-116 in Proc. Symp. Shelterbelts on the Great Plains, Great Plains Agric. Council, Denver, CO 218 pp.

Dailey, T., and D. Redman. 1975. Guidelines for roadless area campsite spacing to minimize impact of human-related noises. U.S.D.A. For. Serv. Gen. Tech. Rpt. PNW-35. Pacific Northwest Forest and Range Exp. Sta., Portland, OR.

Harrison, R. T. 1974. Sound propagation and annoyance under forest conditions, U.S.D.A. Forest Service. Equip. Devel. Center, Equip. Devel. and Test Rpt. 7120-6, San Dimas, CA.

Mulligan, B. E., L. S. Goodman, M. Faupel, S. Lewis, and L. M. Anderson. 1981. Interactive effects of outdoor noise and visible aspects of vegetation on behavior. P. 265-297 in Proc. Southwestern Rec. Research Conf. (1980-1981).

Peterson, E. A., J. S. Augenstein, D. C. Tanis, and D. G. Augenstein. 1981. Noise raises blood pressure without impairing auditory sensitivity. Science 211:1450-1452.

Reethof, G., C. D. Frank, and A. H. McDanial. 1976. Absorption of sound by tree bark. U.S.D.A. For. Serv. Exp. Sta., Upper Darby, PA 6pp.

Shurcliff, W. A. 1970. S/S/T and sonic boom handbook. Ballantine Books, New York. 154 pp.

Van Haverbeck, D. F., and D. I. Cook. 1974. Studies in noise pollution reduction. Amer. Nurseryman Part I and II. June 1 and June 15.

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Last revision July 13, 2001.