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New page: '''Sound''' is a disturbance of mechanical energy that propagates through matter as a wave. Sound is characterized by the [[Wave#Physical description of a wave|properties of wa...
'''Sound''' is a disturbance of [[mechanical energy]] that propagates through [[matter]] as a [[wave]]. Sound is characterized by the [[Wave#Physical description of a wave|properties of waves]], which are [[frequency]], [[wavelength]], [[period]], [[amplitude]], and [[speed of sound|speed]].
Humans perceive sound by the [[sense]] of [[hearing (sense)|hearing]]. By sound, we commonly mean the vibrations that travel through air and are audible to people. However, scientists and engineers use a wider definition of sound that includes low and high [[frequency]] [[vibrations]] in air that cannot be heard by humans, and vibrations that travel through all forms of matter, [[gas]]es, [[liquid]]s, [[solid]]s, and [[plasma (physics)|plasma]]s.
The matter that supports the sound is called the [[Transmission medium|medium]]. Sound propagates as [[waves]] of alternating [[pressure]], causing local regions of [[physical compression|compression]] and [[rarefaction]]. Particles in the medium are displaced by the wave and oscillate. The scientific study of the absorption and reflection of sound waves is called [[acoustics]].
[[Noise]] is often used to refer to an unwanted sound. In science and engineering, noise is an undesirable component that obscures a wanted signal.
==Perception of sound==
Sound is perceived through the [[sense]] of [[hearing (sense)|hearing]]. Humans and many animals use their [[ear]]s to hear sound, but loud sounds and low-frequency sounds can be perceived by other parts of the body through the [[tactition|sense of touch]] as vibrations. Sounds are used in several ways, notably for communication through [[Speech communication|speech]] and [[music]]. They can also be used to acquire information about properties of the surrounding environment such as spatial characteristics and presence of other animals or objects. For example, [[bat]]s use [[animal echolocation|echolocation]], ships and submarines use [[sonar]] and humans can determine spatial information by the way in which they perceive sounds.
Humans can generally hear sounds with frequencies between 20 [[Hertz|Hz]] and 20 [[kHz]] (the audio range) although this range varies significantly with age, occupational hearing damage, and gender; the majority of people can no longer hear 20,000 Hz by the time they are teenagers, and progressively lose the ability to hear higher frequencies as they get older. Most human speech communication takes place between 200 and 8,000 Hz and the human ear is most sensitive to frequencies around 1000-3,500 Hz. Sound above the hearing range is known as [[ultrasound]], and that below the hearing range 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 so a [[logarithm]]ic [[decibel]] amplitude scale is used. The quietest sounds that humans can hear have an amplitude of approximately 20 µPa ([[micropascal]]s) 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, resulting in [[tinnitus]] and [[hearing impairment]]. Sound levels in excess of 130 dB are more than the human ear can safely withstand and can result in serious pain and permanent damage.
At very high amplitudes, sound waves exhibit [[nonlinear]] effects, including [[shock wave|shock]].
The way in which sound travels or propagates is difficult to imagine, as sound is invisible to humans. Imagine a long tube exposed to air whereby sound travels longitudinally through it. The air acts like a [[Slinky]] spring in this tube. As sound is generated at one end, the wave will begin to travel down through the air in the tube. (Watching an earth worm move by pulsating its long body on the top of the ground helps to visualize this same phenomenon). The length of cycle (i.e., the distance between successive bunched up parts of the slinky) will determine the sound wave length. Low bass sounds will have large cycle lengths, in the order of 10-50 feet long, where high treble sounds will have cycle lengths as small as 1/2 an inch.
==Speed of sound==
The speed at which sound travels depends on the medium through which the waves are passing, and is often quoted as a fundamental property of the material. In general, the speed of sound is proportional to the square root of the ratio of the [[elastic modulus]] (stiffness) of the medium and its density. Those physical properties and the speed of sound change with ambient conditions. For example, the speed of sound in air and other gases depends on [[temperature]]. In air at sea level, the speed of sound is approximately 769.5 mph (1,238.3 kph) at 68º F (20º C),[http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe.html Speed of Sound] in water 3,315.1 mph (5,335.1 kph) at 20º C (68º F),[http://hypertextbook.com/facts/2000/NickyDu.shtml Speed of Sound in Water] and in steel 13,332.1 mph (21,446 kph) [http://library.thinkquest.org/19537/Physics4.html The Soundry: The Physics of Sound]. The speed of sound is also slightly sensitive (to second order) to the sound amplitude, resulting in nonlinear propagation effects, such as the weak production of harmonics and the mixing of tones. (see [[parametric array]]).
==Sound pressure==
'''Sound pressure''' is the [[pressure]] deviation from the local ambient pressure caused by a sound [[wave]]. Sound pressure can be measured using a [[microphone]] in air and a [[hydrophone]] in water. The SI unit for sound pressure is the [[pascal (unit)|pascal]] (symbol: Pa). The instantaneous sound pressure is the deviation from the local ambient pressure caused by a sound wave at a given location and given instant in time. The effective sound pressure is the [[root mean square]] of the instantaneous sound pressure averaged over a given interval of time. In a sound wave, the complementary variable to sound pressure is the [[particle velocity|acoustic particle velocity]]. For small amplitudes, sound pressure and particle velocity are linearly related and their ratio is the [[acoustic impedance]]. The acoustic impedance depends on both the characteristics of the wave and the [[Transmission medium|medium]]. The local instantaneous [[sound intensity]] is the product of the sound pressure and the acoustic particle velocity and is, therefore, a vector quantity in time.
The loudest sound ever in air reported was the 1883 volcanic eruption of [[Krakatoa]], whereby sound levels reached 180 dBSPL at a distance of 100 miles (160 km).
==Sound pressure level==
As the human ear can detect sounds with a very wide range of amplitudes, sound pressure is often measured as a level on a logarithmic [[decibel]] scale.
Since the human [[ear]] does not have a flat [[spectral response]], sound pressure levels are often [[frequency]] weighted so that the measured level will match perceived levels more closely. The [[International Electrotechnical Commission]] (IEC) has defined several weighting schemes. [[A-weighting]] attempts to match the response of the human ear to noise and A-weighted sound pressure levels are labeled dBA. C-weighting is used to measure peak levels.
===Examples of sound pressure and sound pressure levels===
See also [[Sound pressure#Examples of sound pressure and sound pressure levels|the Sound pressure article]]. A larger dB chart can be found here:
[[http://makeitlouder.com/Decibel%20Level%20Chart.txt]]
== Equipment for dealing with sound ==
Equipment for generating or using sound includes [[musical instrument]]s, [[hearing aid]]s, [[sonar]] systems and [[sound reproduction]] and broadcasting equipment. Many of these use electro-acoustic transducers such as [[microphone]]s and [[loudspeaker]]s.
==Sound measurement==
*[[Decibel]], [[sone]], [[Mel scale|mel]], [[phon]], [[hertz]]
*[[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 ==
*[[Acoustics]] | [[Auditory imagery]] | [[Audio signal processing]] | [[Beat (acoustics)|Beat]]s | [[Cycle (music)|Cycles]] | [[Diffraction]] | [[Doppler effect]] | [[Echo]] | [[Music]] | [[Note]] | [[Phonons]] | [[Physics of music]] | [[Pitch (music)|Pitch]] | [[Radiation of sound]] | [[Resonance]] | [[Rijke tube]] | [[Reflection (physics)|Reflection]] | [[Reverberation]] | [[Sonic weaponry]] | [[Sound localization]] | [[Soundproofing]] | [[Rotary Woofer]] | [[Steam whistle]] | [[Timbre]] | [[Voyager Golden Record]] | [[Audio bit depth]] | [[Sound branding]] | [[Sounds and Mind]]
== External links ==
*[http://hyperphysics.phy-astr.gsu.edu/hbase/sound/soucon.html HyperPhysics: Sound and Hearing]
*[http://www.acoustics.salford.ac.uk/schools/index.htm Sounds amazing a learning resource for sound and waves]
*[http://www.phys.unsw.edu.au/~jw/hearing.html Hearing curves and on-line hearing test]
*[http://www.audiodesignline.com/howto/audioprocessing/193303241 Audio for the 21st Century]
*[http://www.sengpielaudio.com/calculator-soundlevel.htm Conversion of sound units and levels]
*[http://www.acoustics.salford.ac.uk/schools/index.htm Sounds Amazing a learning resource for sound and waves]
*[http://www.sengpielaudio.com/Calculations03.htm Sound calculations]
----
for more see: [http://en.wikipedia.org/w/index.php?title=Sound&action=edit]
[[Category: General Reference]]
Humans perceive sound by the [[sense]] of [[hearing (sense)|hearing]]. By sound, we commonly mean the vibrations that travel through air and are audible to people. However, scientists and engineers use a wider definition of sound that includes low and high [[frequency]] [[vibrations]] in air that cannot be heard by humans, and vibrations that travel through all forms of matter, [[gas]]es, [[liquid]]s, [[solid]]s, and [[plasma (physics)|plasma]]s.
The matter that supports the sound is called the [[Transmission medium|medium]]. Sound propagates as [[waves]] of alternating [[pressure]], causing local regions of [[physical compression|compression]] and [[rarefaction]]. Particles in the medium are displaced by the wave and oscillate. The scientific study of the absorption and reflection of sound waves is called [[acoustics]].
[[Noise]] is often used to refer to an unwanted sound. In science and engineering, noise is an undesirable component that obscures a wanted signal.
==Perception of sound==
Sound is perceived through the [[sense]] of [[hearing (sense)|hearing]]. Humans and many animals use their [[ear]]s to hear sound, but loud sounds and low-frequency sounds can be perceived by other parts of the body through the [[tactition|sense of touch]] as vibrations. Sounds are used in several ways, notably for communication through [[Speech communication|speech]] and [[music]]. They can also be used to acquire information about properties of the surrounding environment such as spatial characteristics and presence of other animals or objects. For example, [[bat]]s use [[animal echolocation|echolocation]], ships and submarines use [[sonar]] and humans can determine spatial information by the way in which they perceive sounds.
Humans can generally hear sounds with frequencies between 20 [[Hertz|Hz]] and 20 [[kHz]] (the audio range) although this range varies significantly with age, occupational hearing damage, and gender; the majority of people can no longer hear 20,000 Hz by the time they are teenagers, and progressively lose the ability to hear higher frequencies as they get older. Most human speech communication takes place between 200 and 8,000 Hz and the human ear is most sensitive to frequencies around 1000-3,500 Hz. Sound above the hearing range is known as [[ultrasound]], and that below the hearing range 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 so a [[logarithm]]ic [[decibel]] amplitude scale is used. The quietest sounds that humans can hear have an amplitude of approximately 20 µPa ([[micropascal]]s) 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, resulting in [[tinnitus]] and [[hearing impairment]]. Sound levels in excess of 130 dB are more than the human ear can safely withstand and can result in serious pain and permanent damage.
At very high amplitudes, sound waves exhibit [[nonlinear]] effects, including [[shock wave|shock]].
The way in which sound travels or propagates is difficult to imagine, as sound is invisible to humans. Imagine a long tube exposed to air whereby sound travels longitudinally through it. The air acts like a [[Slinky]] spring in this tube. As sound is generated at one end, the wave will begin to travel down through the air in the tube. (Watching an earth worm move by pulsating its long body on the top of the ground helps to visualize this same phenomenon). The length of cycle (i.e., the distance between successive bunched up parts of the slinky) will determine the sound wave length. Low bass sounds will have large cycle lengths, in the order of 10-50 feet long, where high treble sounds will have cycle lengths as small as 1/2 an inch.
==Speed of sound==
The speed at which sound travels depends on the medium through which the waves are passing, and is often quoted as a fundamental property of the material. In general, the speed of sound is proportional to the square root of the ratio of the [[elastic modulus]] (stiffness) of the medium and its density. Those physical properties and the speed of sound change with ambient conditions. For example, the speed of sound in air and other gases depends on [[temperature]]. In air at sea level, the speed of sound is approximately 769.5 mph (1,238.3 kph) at 68º F (20º C),[http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe.html Speed of Sound] in water 3,315.1 mph (5,335.1 kph) at 20º C (68º F),[http://hypertextbook.com/facts/2000/NickyDu.shtml Speed of Sound in Water] and in steel 13,332.1 mph (21,446 kph) [http://library.thinkquest.org/19537/Physics4.html The Soundry: The Physics of Sound]. The speed of sound is also slightly sensitive (to second order) to the sound amplitude, resulting in nonlinear propagation effects, such as the weak production of harmonics and the mixing of tones. (see [[parametric array]]).
==Sound pressure==
'''Sound pressure''' is the [[pressure]] deviation from the local ambient pressure caused by a sound [[wave]]. Sound pressure can be measured using a [[microphone]] in air and a [[hydrophone]] in water. The SI unit for sound pressure is the [[pascal (unit)|pascal]] (symbol: Pa). The instantaneous sound pressure is the deviation from the local ambient pressure caused by a sound wave at a given location and given instant in time. The effective sound pressure is the [[root mean square]] of the instantaneous sound pressure averaged over a given interval of time. In a sound wave, the complementary variable to sound pressure is the [[particle velocity|acoustic particle velocity]]. For small amplitudes, sound pressure and particle velocity are linearly related and their ratio is the [[acoustic impedance]]. The acoustic impedance depends on both the characteristics of the wave and the [[Transmission medium|medium]]. The local instantaneous [[sound intensity]] is the product of the sound pressure and the acoustic particle velocity and is, therefore, a vector quantity in time.
The loudest sound ever in air reported was the 1883 volcanic eruption of [[Krakatoa]], whereby sound levels reached 180 dBSPL at a distance of 100 miles (160 km).
==Sound pressure level==
As the human ear can detect sounds with a very wide range of amplitudes, sound pressure is often measured as a level on a logarithmic [[decibel]] scale.
Since the human [[ear]] does not have a flat [[spectral response]], sound pressure levels are often [[frequency]] weighted so that the measured level will match perceived levels more closely. The [[International Electrotechnical Commission]] (IEC) has defined several weighting schemes. [[A-weighting]] attempts to match the response of the human ear to noise and A-weighted sound pressure levels are labeled dBA. C-weighting is used to measure peak levels.
===Examples of sound pressure and sound pressure levels===
See also [[Sound pressure#Examples of sound pressure and sound pressure levels|the Sound pressure article]]. A larger dB chart can be found here:
[[http://makeitlouder.com/Decibel%20Level%20Chart.txt]]
== Equipment for dealing with sound ==
Equipment for generating or using sound includes [[musical instrument]]s, [[hearing aid]]s, [[sonar]] systems and [[sound reproduction]] and broadcasting equipment. Many of these use electro-acoustic transducers such as [[microphone]]s and [[loudspeaker]]s.
==Sound measurement==
*[[Decibel]], [[sone]], [[Mel scale|mel]], [[phon]], [[hertz]]
*[[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 ==
*[[Acoustics]] | [[Auditory imagery]] | [[Audio signal processing]] | [[Beat (acoustics)|Beat]]s | [[Cycle (music)|Cycles]] | [[Diffraction]] | [[Doppler effect]] | [[Echo]] | [[Music]] | [[Note]] | [[Phonons]] | [[Physics of music]] | [[Pitch (music)|Pitch]] | [[Radiation of sound]] | [[Resonance]] | [[Rijke tube]] | [[Reflection (physics)|Reflection]] | [[Reverberation]] | [[Sonic weaponry]] | [[Sound localization]] | [[Soundproofing]] | [[Rotary Woofer]] | [[Steam whistle]] | [[Timbre]] | [[Voyager Golden Record]] | [[Audio bit depth]] | [[Sound branding]] | [[Sounds and Mind]]
== External links ==
*[http://hyperphysics.phy-astr.gsu.edu/hbase/sound/soucon.html HyperPhysics: Sound and Hearing]
*[http://www.acoustics.salford.ac.uk/schools/index.htm Sounds amazing a learning resource for sound and waves]
*[http://www.phys.unsw.edu.au/~jw/hearing.html Hearing curves and on-line hearing test]
*[http://www.audiodesignline.com/howto/audioprocessing/193303241 Audio for the 21st Century]
*[http://www.sengpielaudio.com/calculator-soundlevel.htm Conversion of sound units and levels]
*[http://www.acoustics.salford.ac.uk/schools/index.htm Sounds Amazing a learning resource for sound and waves]
*[http://www.sengpielaudio.com/Calculations03.htm Sound calculations]
----
for more see: [http://en.wikipedia.org/w/index.php?title=Sound&action=edit]
[[Category: General Reference]]