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`sound
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`sound, any disturbance that travels through an elastic medium such as air, ground, or water to be heard by
`the human ear. When a body vibrates, or moves back and forth (see vibration), the oscillation causes a
`periodic disturbance of the surrounding air or other medium that radiates outward in straight lines in the form
`of a pressure wave. The effect these waves produce upon the ear is perceived as sound. From the point of
`view of physics, sound is considered to be the waves of vibratory motion themselves, whether or not they
`are heard by the human ear.
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`Generation of Sound Waves
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`Sound waves are generated by any vibrating body. For example, when a violin string vibrates upon being
`bowed or plucked, its movement in one direction pushes the molecules of the air before it, crowding them
`together in its path. When it moves back again past its original position and on to the other side, it leaves
`behind it a nearly empty space, i.e., a space with relatively few molecules in it. In the meantime, however,
`the molecules which were at first crowded together have transmitted some of their energy of motion to other
`molecules still farther on and are returning to fill again the space originally occupied and now left empty by
`the retreating violin string. In other words, the vibratory motion set up by the violin string causes alternately
`in a given space a crowding together of the molecules of air (a condensation) and a thinning out of the
`molecules (a rarefaction). Taken together a condensation and a rarefaction make up a sound wave; such a
`wave is called longitudinal, or compressional, because the vibratory motion is forward and backward along
`the direction that the wave is following. Because such a wave travels by disturbing the particles of a material
`medium, sound waves cannot travel through a vacuum.
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`Characteristics of Sound Waves
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`Sounds are generally audible to the human ear if their frequency (number of vibrations per second) lies
`between 20 and 20,000 vibrations per second, but the range varies considerably with the individual. Sound
`waves with frequencies less than those of audible waves are called subsonic; those with frequencies above
`the audible range are called ultrasonic (see ultrasonics).
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`A sound wave is usually represented graphically by a wavy, horizontal line; the upper part of the wave (the
`crest) indicates a condensation and the lower part (the trough) indicates a rarefaction. This graph, however,
`is merely a representation and is not an actual picture of a wave. The length of a sound wave, or the
`wavelength, is measured as the distance from one point of greatest condensation to the next following it or
`from any point on one wave to the corresponding point on the next in a train of waves. The wavelength
`depends upon the velocity of sound in a given medium at a given temperature and upon the frequency of
`vibration. The wavelength of a sound can be determined by dividing the numerical value for the velocity of
`sound in the given medium at the given temperature by the frequency of vibration. For example, if the
`velocity of sound in air is 1,130 ft per second and the frequency of vibration is 256, then the wave length is
`approximately 4.4 ft.
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`The velocity of sound is not constant, however, for it varies in different media and in the same medium at
`different temperatures. For example, in air at 0°C. it is approximately 1,089 ft per second, but at 20°C. it is
`increased to about 1,130 ft per second, or an increase of about 2 ft per second for every centigrade degree
`rise in temperature. Sound travels more slowly in gases than in liquids, and more slowly in liquids than in
`solids. Since the ability to conduct sound is dependent on the density of the medium, solids are better
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`conductors than liquids, liquids are better conductors than gases.
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`Sound waves can be reflected, refracted (or bent), and absorbed as light waves can be. The reflection of
`sound waves can result in an echo—an important factor in the acoustics of theaters and auditoriums. A
`sound wave can be reinforced with waves from a body having the same frequency of vibration, but the
`combination of waves of different frequencies of vibration may produce "beats" or pulsations or may result in
`other forms of interference.
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`Characteristics of Musical Sounds
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`Musical sounds are distinguished from noises in that they are composed of regular, uniform vibrations, while
`noises are irregular and disordered vibrations. Composers, however, frequently use noises as well as
`musical sounds. One musical tone is distinguished from another on the basis of pitch, intensity, or loudness,
`and quality, or timbre. Pitch describes how high or low a tone is and depends upon the rapidity with which a
`sounding body vibrates, i.e., upon the frequency of vibration. The higher the frequency of vibration, the
`higher the tone; the pitch of a siren gets higher and higher as the frequency of vibration increases. The
`apparent change in the pitch of a sound as a source approaches or moves away from an observer is
`described by the Doppler effect. The intensity or loudness of a sound depends upon the extent to which the
`sounding body vibrates, i.e., the amplitude of vibration. A sound is louder as the amplitude of vibration is
`greater, and the intensity decreases as the distance from the source increases. Loudness is measured in
`units called decibels. The sound waves given off by different vibrating bodies differ in quality, or timbre. A
`note from a saxophone, for instance, differs from a note of the same pitch and intensity produced by a violin
`or a xylophone; similarly vibrating reeds, columns of air, and strings all differ. Quality is dependent on the
`number and relative intensity of overtones produced by the vibrating body (see harmonic), and these in turn
`depend upon the nature of the vibrating body.
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`See G. Chedd, Sound (1970).
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` The Columbia Encyclopedia, © Columbia University Press 2013
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`DEFINITION:
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`sound 2 from Chambers 21st Century Dictionary
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`adjective
`1. not damaged or injured; in good condition; healthy The kitten was found safe and sound.
`2 a. sensible; well-founded; reliable sound advice a sound investment;
`(b) said of an argument, opinion, etc: well researched or thought through, logical and convincing.
`3. acceptable or approved of.
`4. severe, hard or thorough a sound spanking.
`5. said of sleep: deep and undisturbed.
`adverb deeply sound asleep.
`Derivatives
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`soundly adverb.
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`soundness noun.
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`[Anglo-Saxon gesund.]
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` Chambers 21st Century Dictionary, © Chambers Harrap Publishers Limited 2001
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`Persistent URL to the Topic: http://search.credoreference.com/content/topic/sound
`
`APA
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`Sound. (2013). In The Columbia Encyclopedia. Retrieved from
`http://search.credoreference.com/content/entry/columency/sound/0
`
`MLA
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`"Sound." The Columbia Encyclopedia. New York: Columbia University Press, 2013. Credo Reference.
`Web. 2 May 2014.
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`Chicago
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`"Sound." In The Columbia Encyclopedia. New York: Columbia University Press, 2013.
`http://search.credoreference.com/content/entry/columency/sound/0 (accessed May 2, 2014.)
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`Harvard
`
`2013 'Sound' in The Columbia Encyclopedia, Columbia University Press, New York, USA. Accessed: 2
`May 2014, from Credo Reference