Sound 27017 225815398 2008-07-15T15:13:39Z VASANTH S.N. 7154392 '''{{Refimprove|date=November 2007}} {{this|audible acoustic waves|Sound (disambiguation)}} {{Redirect|Soundwave|the Transformer|Soundwave (Transformers)}} '''Sound''' is vibration transmitted through a solid, liquid, or gas; particularly, sound means those vibrations composed of frequencies capable of being detected by ears.<ref>{{cite book | authorlink = Houghton Mifflin Company | title = The American Heritage Dictionary of the English Language, Fourth Edition | publisher = Houghton Mifflin Company | date = 2006 | url = http://www.bartleby.com/61/65/S0576500.html }}</ref> == Perception of sound == For humans, hearing is limited to [[frequency|frequencies]] between about 20 [[Hertz|Hz]] and 20,000 Hz (20 [[kHz]]), with the upper limit generally decreasing with age. Other [[species]] have a different range of hearing. For example, dogs can perceive vibrations higher than 20 kHz. As a signal perceived by one of the major [[sense]]s, sound is used by many species for [[defence mechanism (biology)|detecting danger]], [[navigation]], [[predation]], and [[communication]]. [[Earth]]'s [[atmosphere]], [[hydrosphere|water]], and virtually any [[physical phenomenon]], such as [[fire]], [[rain]], [[wind]], [[ocean surface wave|surf]], or [[earthquake]], produces (and is characterized by) its unique sounds. Many species, such as [[frog]]s, [[bird]]s, [[marine mammals|marine]] and terrestrial [[mammal]]s, have also developed special [[organ (anatomy)|organ]]s to produce sound. In some species, these have evolved to produce [[bird vocalization|song]] and (in humans) [[speech communication|speech]]. Furthermore, [[human]]s have developed culture and technology (such as [[music]], [[telephone]] and [[radio]]) that allows them to generate, record, transmit, and broadcast sound. == Physics of sound == The mechanical vibrations that can be interpreted as sound are able to travel through all [[State of matter|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 cannot travel through [[vacuum]]. ===Longitudinal and transverse waves=== Sound is transmitted through gases, plasma, and liquids as [[longitudinal wave]]s, also called [[compression]] waves. Through solids, however, it can be transmitted as both [[longitudinal wave|longitudinal]] and [[transverse wave]]s. Longitudinal sound waves are waves of alternating [[pressure]] deviations from the [[equilibrium]] pressure, causing local regions of [[physical compression|compression]] and [[rarefaction]], while [[transverse wave]]s in solids, are waves of alternating [[shear stress]]. Matter in the medium is periodically displaced by a sound wave, and thus oscillates. The energy carried by the sound wave converts back and forth between the potential energy of the extra [[physical compression|compression]] (in case of longitudinal waves) or lateral displacement [[Strain (materials science)|strain]] (in case of transverse waves) of the matter and the kinetic energy of the oscillations of the medium. ===Sound wave properties and characteristics=== Sound waves are characterized by the generic [[Wave#Physical description of a wave|properties of waves]], which are [[frequency]], [[wavelength]], [[Periodicity|period]], [[amplitude]], [[Intensity (physics)|intensity]], [[speed of sound|speed]], and [[Direction (geometry, geography)|direction]] (sometimes speed and direction are combined as a [[velocity]] [[Vector (spatial)|vector]], or wavelength and direction are combined as a [[wave vector]]). [[Transverse wave]]s, also known as [[Shear stress|shear]] waves, have an additional property of [[polarization]]. Sound characteristics can depend on the type of sound waves (longitudinal versus transverse) as well as on the [[physical properties]] of the transmission medium. Whenever the [[pitch]] of the soundwave is affected by some kind of change, the distance between the sound wave maxima also changes, resulting in a change of [[frequency]]. When the loudness of a soundwave changes, so does the amount of compression in airwave that is travelling through it, which in turn can be defined as [[amplitude]]. ===Speed of sound=== {{main|Speed of sound}} The speed of sound 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 to its [[density]]. Those physical properties and the speed of sound change with ambient conditions. For example, the speed of sound in gases depends on [[temperature]]. In 20°C (68°F) air at sea level, the speed of sound is approximately 343 m/s (767.3 mph). In fresh water, also at 20°C, the speed of sound is approximately 1482 m/s (3,315.1 mph). In steel the speed of sound is about 5960 m/s (13,332.1 mph).<ref>[http://library.thinkquest.org/19537/Physics4.html The Soundry: The Physics of Sound]</ref> The speed of sound is also slightly sensitive (a second-order effect) to the sound amplitude, which means that there are nonlinear propagation effects, such as the production of harmonics and mixed tones not present in the original sound (see [[parametric array]]). ===Acoustics and noise=== The scientific study of the propagation, absorption, and reflection of sound waves is called [[acoustics]]. [[Noise]] is a term often used to refer to an unwanted sound. In science and engineering, noise is an undesirable component that obscures a wanted signal. ==Sound pressure level== {{main|Sound pressure}} {{Sound measurements}} Sound pressure is defined as the difference between the average local pressure of the medium outside of the sound wave in which it is traveling through (at a given point and a given time) and the pressure found within the sound wave itself within that same medium. A square of this difference (i.e. a square of the deviation from the equilibrium pressure) is usually averaged over time and/or space, and a square root of such average is taken to obtain a [[root mean square]] (RMS) value. For example, 1 [[Pascal (unit)|Pa]] RMS sound pressure in atmospheric air implies that the actual pressure in the sound wave oscillates between (1 atm <math>-\sqrt{2}</math> Pa) and (1 atm <math>+\sqrt{2}</math> Pa), that is between 101323.6 and 101326.4 Pa. Such a tiny (relative to atmospheric) variation in air pressure at an [[audio frequency]] will be perceived as quite a [[deaf]]ening sound, and can cause hearing damage, according to the table below. 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. The '''sound pressure level''' (SPL) or ''L''<sub>p</sub> is defined as :<math> L_\mathrm{p}=10\, \log_{10}\left(\frac{{p}^2}{{p_\mathrm{ref}}^2}\right) =20\, \log_{10}\left(\frac{p}{p_\mathrm{ref}}\right)\mbox{ dB} </math> :where ''p'' is the [[root-mean-square]] sound pressure and <math>p_\mathrm{ref}</math> is a reference sound pressure. Commonly used reference sound pressures, defined in the standard [[American National Standards Institute|ANSI]] S1.1-1994, are 20 [[micropascal|µPa]] in air and 1 [[micropascal|µPa]] in water. Without a specified reference sound pressure, a value expressed in decibels cannot represent a sound pressure level. Since the human [[ear]] does not have a flat [[spectral response]], sound pressures 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===<!-- This section is linked from [[Decibel]] --> {| class="wikitable" ! Source of sound !! [[root mean square|RMS]] sound pressure !! sound pressure level |- ! &#160; !! align="center" | [[Pascal_(unit)|Pa]] !! align="center" | [[Decibel|dB]] re 20 µPa |- |Theoretical limit for undistorted sound at<br>1 [[atmosphere (unit)|atmosphere]] environmental [[pressure]] || align="right" | 101,325 || align="right" | 191 |- |1883 [[Krakatoa]] eruption|| align="right" | || align="right" | approx 180 at 100 miles |- |[[Stun grenades]]|| align="right" | || align="right" | 170-180 |- |rocket launch equipment acoustic tests || align="right" | || align="right" | approx. 165 |- |[[threshold of pain]] || align="right" | 100 || align="right" | 134 |- |hearing damage during short-term effect || align="right" | 20 || align="right" | approx. 120 |- |[[jet engine]], 100 m distant || align="right" | 6–200 || align="right" | 110–140 |- |[[jackhammer]], 1 m distant / [[discotheque]] || align="right" | 2 || align="right" | approx. 100 |- |[[hearing damage]] from long-term exposure || align="right" | 0.6 || align="right" | approx. 85 |- |traffic noise on major road, 10 m distant || align="right" | 0.2–0.6 || align="right" | 80–90 |- |moving [[automobile]], 10 m distant || align="right" | 0.02–0.2 || align="right" | 60–80 |- |TV set – typical home level, 1 m distant || align="right" | 0.02 || align="right" | approx. 60 |- |normal talking, 1 m distant || align="right" | 0.002–0.02 || align="right" | 40–60 |- |very calm room || align="right" | 0.0002–0.0006 || align="right" | 20–30 |- |quiet rustling leaves, calm human breathing || align="right" | 0.00006 || align="right" | 10 |- |[[auditory threshold]] at 2 kHz – undamaged human ears || align="right" | 0.00002 || align="right" | 0 |} == 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. == References == <references/> ==Sound measurement== <div class="references-small" style="-moz-column-count:2; column-count:2;"> *[[Decibel]], [[sone]], [[Mel scale|mel]], [[phon]], [[hertz]] *[[Sound pressure level]] *[[Particle velocity]], [[acoustic velocity]] *[[Particle displacement]], [[particle amplitude]], [[particle acceleration]] *[[Sound power]], [[acoustic power]], [[sound power level]] *[[Sound energy flux]] *[[Sound intensity]], [[acoustic intensity]], [[sound intensity level]] *[[Acoustic impedance]], [[sound impedance]], [[characteristic impedance]] *[[Speed of sound]], [[amplitude]] *See also [[Template:Sound measurements]] </div> == See also == [[Pitch]] [[Acoustics]] | [[Auditory imagery]] | [[Audio bit depth]] | [[Audio signal processing]] | [[Beat (acoustics)|Beat]]s | [[Cycle (music)|Cycles]] | [[Diffraction]] | [[Doppler effect]] | [[Echo (phenomenon)|Echo]] | [[Music]] | [[Note]] | [[Phonons]] | [[Physics of music]] | [[Pitch (music)|Pitch]] | [[Psychoacoustics]] | [[Resonance]] | [[Rijke tube]] | [[Reflection (physics)|Reflection]] | [[Reverberation]] | [[Sonic weaponry]] | [[Sound localization]] | [[Soundproofing]] | [[Timbre]] | == External links == {{wikiquote}} {{wikibooks}} *[http://hyperphysics.phy-astr.gsu.edu/hbase/sound/soucon.html HyperPhysics: Sound and Hearing] *[http://podcomplex.com/guide/physics.html Introduction to the Physics of Sound] *[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] *[http://www.audiocheck.net Audio Check: a free collection of audio tests and test tones playable on-line] [[Category:Sound ]] [[Category:Acoustics]] [[Category:Hearing]] [[Category:Waves]] [[gan:聲氣]] [[af:Klank]] [[ar:صوت]] [[bn:শব্দ]] [[bs:Zvuk]] [[bg:Звук]] [[ca:So]] [[cs:Zvuk]] [[cy:Sain]] [[da:Lyd]] [[de:Schall]] [[et:Heli]] [[el:Ήχος]] [[es:Sonido]] [[eo:Sono]] [[eu:Soinu]] [[fa:صدا]] [[fr:Son (physique)]] [[ga:Fuaim]] [[gl:Son]] [[ko:소리]] [[hr:Zvuk]] [[io:Sono]] [[id:Bunyi]] [[is:Hljóð]] [[it:Suono]] [[he:קול]] [[la:Sonus (physica)]] [[lv:Skaņa]] [[lt:Garsas]] [[jbo:sance]] [[hu:Hang]] [[mk:Звук]] [[ml:ശബ്ദം]] [[mr:आवाज (ध्वनी)]] [[ms:Bunyi]] [[nl:Geluid]] [[ne:ध्वनि]] [[new:सः]] [[ja:音]] [[no:Lyd]] [[nn:Lyd]] [[uz:Tovush]] [[pl:Dźwięk]] [[pt:Som]] [[ro:Sunet]] [[qu:Ruqyay]] [[ru:Звук]] [[simple:Sound]] [[sk:Zvuk]] [[sl:Zvok]] [[sr:Звук]] [[sh:Zvuk]] [[su:Sora]] [[fi:Ääni]] [[sv:Ljud]] [[ta:ஒலி]] [[te:ధ్వని]] [[th:เสียง]] [[vi:Âm thanh]] [[tr:Ses (enerji)]] [[uk:Звук]] [[fiu-vro:Helü]] [[zh-yue:聲]] [[zea:Geluud]] [[zh:声音]] [[kn:ಶಬ್ದ]]