NOISE AND ITS CONTROL. No rigid definition of noise is possible. By analogy with "dirt," it has been called "sound out of place," and it is usually a medley of individual sounds. For measuring noise the instrument most widely used, especially in America, is the audiometer devised by the Bell Telephone Labora tories, in which the noise is matched in the observer's ear against a standard noise produced by the instrument. In England meas urements have been made with an electric audiometer invented by Mr. A. M. Low. "Noise units" have been used to express such measurements but most of these are of comparative value only. For scientific purposes the units should be purely physical; for example, to dynes per square centimeter.
A comprehensive survey of the intensity and sources of city noise was made in 1925 and 1926 in New York city. Partial surveys have been made in London, Chicago, Boston, Washington and other cities. The noisiest normal street corner so far dis covered anywhere in the world is the corner of Sixth avenue and Thirty-Fourth street in New York city; an intersection of three main highways, three surface car lines and a double-track line of the elevated railway. At this corner the noise intensity is suffi cient to make the normal individual about two-thirds deaf. Noise intensity in exceptional places, like railway subways or noisy factories, may be twice or three times greater than this. On the average busy street of an American city the day-time noise is sufficient to render the normal individual one-fourth to one-third deaf. The ebb and flow of noise from hour to hour during the 24-hour day parallels precisely the increase and decrease of vehicular traffic on the streets. In physical units the New York city street noise was found to vary between o•oo r dynes per square centimeter and 20 dynes, averaging about 5 dynes.
Approximately 40% of the noise could be traced to the auto mobile trucks used for commercial deliveries; 25% to the elevated railway, and 20% to the surface cars. The remaining 15% was supplied by private automobiles, taxicabs, automobile horns, horse drawn vehicles, riveting and excavating machines, alarm signals of the fire and police departments and other occasional noise producers. At no place on city streets do human speech and human feet make measurable contributions to the noise. At windows street noise decreases with height, but much less so than would be expected from the physical law of attenuation of sounds in the open air, the discrepancy being due to reflection of the noise between the buildings on the two sides of the street.
The usual assumption that noise is harmful to man is by no means proved. Noise is known to affect the human heart beat as well as the rate at which heat energy is set free in the human body, buL the details of these effects have not been studied. Most individuals accustom themselves to living or working in noisy surroundings and only nervous individuals who fail to make this adjustment suffer harmful effects. It has been urged that the greater use of bodily energy in noisy surroundings may cause bodily ills. Searching investigations of these problems are now (1929) under way in several American laboratories of psychology. Contrary to the usual opinion, there is no dependable evidence that life or work in noisy places decreases the acuteness of hear ing, except during the first few minutes after the noise ceases.
Much noise could be prevented by denying use of the streets to vehicles improperly cared for, and which rattle or squeak, espe cially automobile trucks; also by preventing loose, rattling parts on surface cars and by removing loose or wide crossings in the rails of street railways and by restricting the blowing of horns. It is possible that the average street noise of a city could be reduced at least one half by adequate enforcement of such regula tions. The construction of noise-proof rooms or noise-proof houses is possible on well-known principles of architectural acous tics but is too expensive for general use. (E. E. F.) Law.—In law noise may be defined as an excessive, offensive, persistent or startling sound. By the common law of England freedom from noise is essential to the full enjoyment of a dwell ing house, and acts which affect that enjoyment may be actionable as nuisances. But it has been laid down that a nuisance by noise, supposing malice to be out of the question, is emphatically a question of degree (Gaunt v. Finney, 1872, 8 Ch. Ap. 8). The noise must be exceptional and unreasonable. The ringing of bells, building operations, vibration of machinery, fireworks, bands, a circus, merry-go-rounds, collecting disorderly crowds, dancing, singing, etc., have been held under certain circumstances to con stitute nuisances so as to interfere with quiet and comfort, and have been restrained by injunction. Noise occasioned by the frequent repetition of street cries is frequently the subject of local by-laws, which impose penalties for infringement.