Sound

Sound measurements
	Sound pressure p
	Sound pressure level (SPL)
	Particle velocity v
	Particle velocity level (SVL)
	(Sound velocity level)
	Particle displacement ξ
	Sound intensity I
	Sound intensity level (SIL)
	Sound power Pac
	Sound power level (SWL)
	Sound energy density E
	Sound energy flux q
	Acoustic impedance Z
	Speed of sound c

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This article is about compression waves. For other meanings, see sound (disambiguation).

File:Processing of sound.jpg

A schematic representation of hearing. (Blue: sound waves. Red: eardrum. Yellow: cochlea. Green: auditory receptor cells. Purple: frequency spectrum of hearing response. Orange: nerve impulse.)

Sound is a disturbance of mechanical energy that propagates through matter as a wave. Humans perceive sound by the sense of hearing.

By sound is generally meant the vibrations that travel through air and can be heard by humans. However, scientists and engineers use a wider definition of sound that includes low and high frequency vibrations in air that cannot be heard, and vibrations that travel through all forms of matter, gases, liquids and solids. The matter that supports the sound is called the medium. Sound propagates as waves of alternating pressure, causing local regions of compression and rarefaction. Particles in the medium are displaced by the wave and oscillate.

As a wave, sound is characterized by the properties of waves including frequency, wavelength, period, amplitude and velocity or speed.

The scientific study of sound is called acoustics.

Noise and sound often mean the same thing; when they differ, a noise is an unwanted sound. In science and engineering, noise is an undesirable component that obscures a signal. What is noise and what is signal depends on your point of view.

Perception of sound

Sound is perceived through the sense of hearing. Humans and many animals use their ears to hear sound, but loud sounds and low frequency sounds can be perceived by other parts of the body through the sense of touch. Sounds are used in several ways, most notably for communication through speech or, for example, music. Sound can also be used to acquire information about the surrounding environment in properties such as spatial characteristics and presence of other animals or objects. For example, bats use echolocation, ships and submarines use sonar, and humans can determine spatial information by the way in which they perceive sounds.

The range of frequencies that humans can hear is approximately between 20 Hz and 20,000 Hz. This range is by definition the audible spectrum, but some people (particularly women) can hear above 20,000 Hz. This range varies by individual and generally shrinks with age, mostly in the upper part of the spectrum. The ear is most sensitive to frequencies around 3,500 Hz. Sound above 20,000 Hz is known as ultrasound; sound below 20 Hz as infrasound.

The amplitude of a sound wave is specified in terms of its pressure. The human ear can detect sounds with a very wide range of amplitudes and a logarithmic decibel amplitude scale is used. The quietest sounds that humans can hear have an amplitude of approximately 20 μPa (micropascals) or a sound pressure level (SPL) of 0 dB re 20 μPa (often incorrectly abbreviated as 0 dB SPL). Prolonged exposure to a sound pressure level exceeding 85 dB can permanently damage the ear and sometimes resulting in tinnitus and hearing impairment. Sound levels in excess of 130 dB are considered upward of what the human ear can withstand and may result in serious pain and permanent damage. At very high amplitudes, sound waves exhibit non-linear effects including shock.

Measurement of sound

Decibel, sone, mel, phon
Sound pressure, acoustic pressure, sound pressure level
Particle velocity, acoustic velocity, sound velocity
Particle displacement, particle amplitude, particle acceleration
Sound power, acoustic power, sound power level
Sound intensity, acoustic intensity, sound intensity level
Acoustic impedance, sound impedance, characteristic impedance
Speed of sound, amplitude
Sound energy flux
See also Template:Sound measurements

References
ISBN links support NWE through referral fees

Olson, Harry F, "Acoustical Engineering" (1957) cited in Roads, Curtis (2001). Microsound. MIT. ISBN 0262182157.
Roederer, Juan C. Introduction to the Physics and Psychophysics of Music (2nd ed.). New York: Springer-Verlag, 1979.
Charles Dodge and Thomas A. Jerse, "Computer Music". New York, Schirmer Books, 1997. ISBN 0028646827
Grey, J. M. "An Exploration of Musical Timbre." Doctoral dissertation, Stanford University, 1975.

External links

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Sound

af:Klank ar:صوت bn:শব্দ bg:Звук bs:Zvuk ca:So cs:Zvuk da:Lyd de:Schall es:Sonido eo:Sono eu:Soinu fr:Son (physique) gl:Son ko:소리 hr:Zvuk io:Sono id:Bunyi it:Suono he:קול jbo:sance mk:Звук hu:Hang nl:Geluid ja:音 no:Lyd nn:Lyd pl:Dźwięk pt:Som ro:Sunet ru:Звук simple:Sound sl:Zvok fi:Ääni sv:Ljud ta:ஒலி th:เสียง uk:Звук zh:声音

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