1
Capital Cities - Safe And Sound (Official Video)
Capital Cities - Safe And Sound (Official Video)
DATE: 2013/04/25::
2
Rain Sounds 10 Hours:The Sound of Rain Meditation,Autogenc Training, Deep Sleep,Relaxing Sounds
Rain Sounds 10 Hours:The Sound of Rain Meditation,Autogenc Training, Deep Sleep,Relaxing Sounds
DATE: 2012/10/13::
3
Relax 8 Hours-Relaxing Nature Sounds-Study-Sleep-Meditation-Water Sounds-Bird Song
Relax 8 Hours-Relaxing Nature Sounds-Study-Sleep-Meditation-Water Sounds-Bird Song
DATE: 2013/07/02::
4
Shawn Hook - Sound Of Your Heart
Shawn Hook - Sound Of Your Heart
DATE: 2015/03/27::
5
End Times | MORE Strange
End Times | MORE Strange 'Trumpet' Sounds coming from SKY
DATE: 2015/05/19::
6
5 Most Mysterious Sounds Ever Recorded
5 Most Mysterious Sounds Ever Recorded
DATE: 2014/01/03::
7
Sound of Freedom:  The PFI Gun Store Visit
Sound of Freedom: The PFI Gun Store Visit
DATE: 2015/07/03::
8
Ministry of Sound - 23rd Birthday Mix
Ministry of Sound - 23rd Birthday Mix
DATE: 2014/09/19::
9
DieAussenseiter - Was Immer (Offizielles Musikvideo) - SOUND OF YOUR LIFE
DieAussenseiter - Was Immer (Offizielles Musikvideo) - SOUND OF YOUR LIFE
DATE: 2015/07/05::
10
Amerikan Sound Megamix
Amerikan Sound Megamix
DATE: 2014/07/28::
11
Vazquez Sounds Adele - Rolling In The Deep (Cover)
Vazquez Sounds Adele - Rolling In The Deep (Cover)
DATE: 2011/11/11::
12
Teen Titans GO! "And The Award for Sound Design Goes To Robin" Ending Scene
Teen Titans GO! "And The Award for Sound Design Goes To Robin" Ending Scene
DATE: 2015/07/04::
13
Teen Titans GO! "And The Award for Sound Design Goes To Robin" Clip:3
Teen Titans GO! "And The Award for Sound Design Goes To Robin" Clip:3
DATE: 2015/07/04::
14
Teen Titans GO! "And The Award for Sound Design Goes To Robin" Clip:2
Teen Titans GO! "And The Award for Sound Design Goes To Robin" Clip:2
DATE: 2015/07/04::
15
Transmission of Sound - Designmate
Transmission of Sound - Designmate
DATE: 2012/06/21::
16
Alberto - Sound Of Your Life (Offizielles Musikvideo)
Alberto - Sound Of Your Life (Offizielles Musikvideo)
DATE: 2015/07/05::
17
Nature Sound 16 - THE MOST RELAXING SOUNDS -
Nature Sound 16 - THE MOST RELAXING SOUNDS -
DATE: 2011/10/11::
18
[No Talking Sound ASMR] 파도 소리 Wave Sound (bit windy)
[No Talking Sound ASMR] 파도 소리 Wave Sound (bit windy)
DATE: 2015/07/04::
19
Teen Titans GO! "And The Award for Sound Design Goes To Robin"
Teen Titans GO! "And The Award for Sound Design Goes To Robin"
DATE: 2015/07/04::
20
Sound Like John Mayer Without Busting The Bank – Rabea Massaad and Matt Hornby
Sound Like John Mayer Without Busting The Bank – Rabea Massaad and Matt Hornby
DATE: 2015/07/03::
21
The Sounds of a Box Fan 8hrs "Sleep Sounds"
The Sounds of a Box Fan 8hrs "Sleep Sounds"
DATE: 2012/11/09::
22
How my girlfriend thinks Heroes of the Storm players sound.
How my girlfriend thinks Heroes of the Storm players sound.
DATE: 2015/07/04::
23
Safe & Sound feat. The Civil Wars (The Hunger Games: Songs From District 12 And Beyond)
Safe & Sound feat. The Civil Wars (The Hunger Games: Songs From District 12 And Beyond)
DATE: 2012/02/16::
24
Lamborghini Aventador LP750 SV Exhaust Sound - Starts, Accelerations, FlyBys & More!
Lamborghini Aventador LP750 SV Exhaust Sound - Starts, Accelerations, FlyBys & More!
DATE: 2015/07/04::
25
The Coolest Things Sound Waves Do
The Coolest Things Sound Waves Do
DATE: 2013/07/20::
26
GIFs With Sound #146 2015 GWS4ALL JULY
GIFs With Sound #146 2015 GWS4ALL JULY
DATE: 2015/07/01::
27
What Does Sound Look Like?
What Does Sound Look Like?
DATE: 2014/04/09::
28
Amazing Water & Sound Experiment #2
Amazing Water & Sound Experiment #2
DATE: 2013/03/11::
29
The Sound of Silence (Original Version from 1964)
The Sound of Silence (Original Version from 1964)
DATE: 2009/12/22::
30
GTA 5 PC MOD - Gun Sound Overhaul MOD (New & Updated Gun Sound Effects!!)
GTA 5 PC MOD - Gun Sound Overhaul MOD (New & Updated Gun Sound Effects!!)
DATE: 2015/07/04::
31
Battle of the smartphones blind test - Sound (full version)
Battle of the smartphones blind test - Sound (full version)
DATE: 2015/07/03::
32
DJ Fresh VS Jay Fay Feat. Ms Dynamite -
DJ Fresh VS Jay Fay Feat. Ms Dynamite - 'Dibby Dibby Sound' (Official Video)
DATE: 2013/12/16::
33
Lee Brice - That Don
Lee Brice - That Don't Sound Like You (Official Music Video)
DATE: 2015/07/01::
34
GIFs With Sound #42 FAN FRIDAY JULY 2015 GWS4ALL
GIFs With Sound #42 FAN FRIDAY JULY 2015 GWS4ALL
DATE: 2015/07/03::
35
Fun Science: Sound
Fun Science: Sound
DATE: 2011/08/27::
36
Best of The Sound You Need
Best of The Sound You Need
DATE: 2014/10/05::
37
Calming Seas 1 - 11 Hours Ocean Sound for relaxation, yoga, meditation, reading, sleep, study
Calming Seas 1 - 11 Hours Ocean Sound for relaxation, yoga, meditation, reading, sleep, study
DATE: 2013/08/07::
38
Mad Mike Raw 4rotor MADBUL sound Goodwood Festival of Speed 2015
Mad Mike Raw 4rotor MADBUL sound Goodwood Festival of Speed 2015
DATE: 2015/07/02::
39
Funny sound Ganon
Funny sound Ganon
DATE: 2015/07/04::
40
GIFs With Sound #136 2015 GWS4ALL MAY
GIFs With Sound #136 2015 GWS4ALL MAY
DATE: 2015/05/24::
41
11 hrs. Healing Sea - No music - Gentle ocean waves - Soothing sound of ocean
11 hrs. Healing Sea - No music - Gentle ocean waves - Soothing sound of ocean
DATE: 2015/03/22::
42
Sound,Bass,Water, Sound makes water come alive with cymatics
Sound,Bass,Water, Sound makes water come alive with cymatics
DATE: 2013/10/09::
43
Sylwia Grzeszczak feat. Sound
Sylwia Grzeszczak feat. Sound'n'Grace - Kiedy tylko spojrzę [Official Music Video]
DATE: 2015/05/08::
44
Tabb & Sound
Tabb & Sound'n'Grace - Dach (Oficjalny Teledysk)
DATE: 2015/02/15::
45
New World Sound & Thomas Newson - Flute (Original Mix)
New World Sound & Thomas Newson - Flute (Original Mix)
DATE: 2013/11/11::
46
The Sound You Need Mix #3 - [Summer Vibes 2014 | Mixed by LRBZ]
The Sound You Need Mix #3 - [Summer Vibes 2014 | Mixed by LRBZ]
DATE: 2014/08/04::
47
An Epic Return: The Music And Sound Of Halo 5
An Epic Return: The Music And Sound Of Halo 5
DATE: 2015/07/02::
48
Pink Floyd - Delicate Sound Of Thunder - Album (1988)
Pink Floyd - Delicate Sound Of Thunder - Album (1988)
DATE: 2015/05/03::
49
Do you Need a Sound Card?
Do you Need a Sound Card?
DATE: 2015/06/27::
50
Kiesza - Sound Of A Woman
Kiesza - Sound Of A Woman
DATE: 2015/04/10::
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From Wikipedia, the free encyclopedia
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This article is about audible acoustic waves. For other uses, see Sound (disambiguation).
A drum produces sound via a vibrating membrane.

In physics, sound is a vibration that propagates as a typically audible mechanical wave of pressure and displacement, through a medium such as air or water. In physiology and psychology, sound is the reception of such waves and their perception by the brain.[1]

Acoustics[edit]

Audio engineers in R&D design audio equipment

Acoustics is the interdisciplinary science that deals with the study of mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound, and infrasound. A scientist who works in the field of acoustics is an acoustician, while someone working in the field of acoustical engineering may be called an acoustical engineer.[2] An audio engineer, on the other hand is concerned with the recording, manipulation, mixing, and reproduction of sound.

Applications of acoustics are found in almost all aspects of modern society, subdisciplines include aeroacoustics, audio signal processing, architectural acoustics, bioacoustics, electro-acoustics, environmental noise, musical acoustics, noise control, psychoacoustics, speech, ultrasound, underwater acoustics, and vibration.[3]

Definition[edit]

Sound is defined by ANSI/ASA S1.1-2013 as "(a) Oscillation in pressure, stress, particle displacement, particle velocity, etc., propagated in a medium with internal forces (e.g., elastic or viscous), or the superposition of such propagated oscillation. (b) Auditory sensation evoked by the oscillation described in (a)."

Physics of sound[edit]

Sound can propagate through compressible media such as air, water and solids as longitudinal waves and also as a transverse waves in solids (see Longitudinal and transverse waves, below). The sound waves are generated by a sound source, such as the vibrating diaphragm of a stereo speaker. The sound source creates vibrations in the surrounding medium. As the source continues to vibrate the medium, the vibrations propagate away from the source at the speed of sound, thus forming the sound wave. At a fixed distance from the source, the pressure, velocity, and displacement of the medium vary in time. At an instant in time, the pressure, velocity, and displacement vary in space. Note that the particles of the medium do not travel with the sound wave. This is intuitively obvious for a solid, and the same is true for liquids and gases (that is, the vibrations of particles in the gas or liquid transport the vibrations, while the average position of the particles over time does not change). During propagation, waves can be reflected, refracted, or attenuated by the medium.[4]

The behavior of sound propagation is generally affected by three things:

  • A relationship between density and pressure. This relationship, affected by temperature, determines the speed of sound within the medium.
  • The propagation is also affected by the motion of the medium itself. For example, sound moving through wind. Independent of the motion of sound through the medium, if the medium is moving, the sound is further transported.
  • The viscosity of the medium also affects the motion of sound waves. It determines the rate at which sound is attenuated. For many media, such as air or water, attenuation due to viscosity is negligible.

When sound is moving through a medium that does not have constant physical properties, it may be refracted (either dispersed or focused).[4]

Spherical compression (longitudinal) waves

The mechanical vibrations that can be interpreted as sound are able to travel through all forms of matter: gases, liquids, solids, and plasmas. The matter that supports the sound is called the medium. Sound cannot travel through a vacuum.

Longitudinal and transverse waves[edit]

Sound is transmitted through gases, plasma, and liquids as longitudinal waves, also called compression waves. It requires a medium to propagate. Through solids, however, it can be transmitted as both longitudinal waves and transverse waves. Longitudinal sound waves are waves of alternating pressure deviations from the equilibrium pressure, causing local regions of compression and rarefaction, while transverse waves (in solids) are waves of alternating shear stress at right angle to the direction of propagation.

Sound waves may be "viewed" using parabolic mirrors and objects that produce sound.[5]

The energy carried by an oscillating sound wave converts back and forth between the potential energy of the extra compression (in case of longitudinal waves) or lateral displacement strain (in case of transverse waves) of the matter, and the kinetic energy of the displacement velocity of particles of the medium.

Sound wave properties and characteristics[edit]

Sinusoidal waves of various frequencies; the bottom waves have higher frequencies than those above. The horizontal axis represents time.

Sound waves are often simplified to a description in terms of sinusoidal plane waves, which are characterized by these generic properties:

Sound that is perceptible by humans has frequencies from about 20 Hz to 20,000 Hz. In air at standard temperature and pressure, the corresponding wavelengths of sound waves range from 17 m to 17 mm. Sometimes speed and direction are combined as a velocity vector; wave number and direction are combined as a wave vector.

Transverse waves, also known as shear waves, have the additional property, polarization, and are not a characteristic of sound waves.

Speed of sound[edit]

U.S. Navy F/A-18 approaching the sound barrier. The white halo is formed by condensed water droplets thought to result from a drop in air pressure around the aircraft (see Prandtl-Glauert Singularity).[6]

The speed of sound depends on the medium that the waves pass through, and is a fundamental property of the material. The first significant effort towards the measure of the speed of sound was made by Newton. He believed that the speed of sound in a particular substance was equal to the square root of the pressure acting on it (STP) divided by its density.


c = \sqrt{ {p \over \rho}}\,

This was later proven wrong when found to incorrectly derive the speed. French mathematician Laplace corrected the formula by deducing that the phenomenon of sound travelling is not isothermal, as believed by Newton, but adiabatic. He added another factor to the equation-gamma-and multiplied 
\sqrt{\gamma}\,
to \sqrt{ {p \over \rho}}\,, thus coming up with the equation 
c = \sqrt{\gamma \cdot {p \over \rho}}\,
. Since 
K = \gamma \cdot p\,
the final equation came up to be 
c = \sqrt{\frac{K}{\rho}}\,
which is also known as the Newton-Laplace equation. In this equation, K = elastic bulk modulus, c = velocity of sound, and  {\rho}\, = density. Thus, the speed of sound is proportional to the square root of the ratio of the bulk modulus 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 (1,230 km/h; 767 mph) using the formula "v = (331 + 0.6 T) m/s". In fresh water, also at 20 °C, the speed of sound is approximately 1,482 m/s (5,335 km/h; 3,315 mph). In steel, the speed of sound is about 5,960 m/s (21,460 km/h; 13,330 mph). The speed of sound is also slightly sensitive (a second-order anharmonic effect) to the sound amplitude, which means that there are non-linear propagation effects, such as the production of harmonics and mixed tones not present in the original sound (see parametric array).

Perception of sound[edit]

Main article: Loudness
Human ear

A distinct use of the term sound from its use in physics is that in physiology and psychology, where the term refers to the subject of perception by the brain. The field of psychoacoustics is dedicated to such studies.

The physical reception of sound in any hearing organism is limited to a range of frequencies. Humans normally hear sound frequencies between approximately 20 Hz and 20,000 Hz (20 kHz),[7]:382 The upper limit decreases with age.[7]:249

Other species have a different range of hearing. For example, dogs can perceive vibrations higher than 20 kHz, but are deaf below 40 Hz. As a signal perceived by one of the major senses, sound is used by many species for detecting danger, navigation, predation, and communication. Earth's atmosphere, water, and virtually any physical phenomenon, such as fire, rain, wind, surf, or earthquake, produces (and is characterized by) its unique sounds. Many species, such as frogs, birds, marine and terrestrial mammals, have also developed special organs to produce sound. In some species, these produce song and speech. Furthermore, humans have developed culture and technology (such as music, telephone and radio) that allows them to generate, record, transmit, and broadcast sound.

Sometimes sound refers to only those vibrations with frequencies that are within the hearing range for humans[8] or for a particular animal.

Noise[edit]

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[edit]

Main article: Sound pressure level
Sound measurements
Characteristic
Symbols
 Sound pressure  p, SPL
 Particle velocity  v, SVL
 Particle displacement  ξ
 Sound intensity  I, SIL
 Sound power  P, SWL
 Sound energy  W
 Sound energy density  w
 Sound exposure  E, SEL
 Acoustic impedance  Z
 Speed of sound  c
 Audio frequency  AF
 Transmission loss  TL

Sound pressure is the difference, in a given medium, between average local pressure and the pressure in the sound wave. 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 this average provides a root mean square (RMS) value. For example, 1 Pa RMS sound pressure (94 dBSPL) in atmospheric air implies that the actual pressure in the sound wave oscillates between (1 atm -\sqrt{2} Pa) and (1 atm +\sqrt{2} Pa), that is between 101323.6 and 101326.4 Pa. As the human ear can detect sounds with a wide range of amplitudes, sound pressure is often measured as a level on a logarithmic decibel scale. The sound pressure level (SPL) or Lp is defined as


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}\,
where p is the root-mean-square sound pressure and p_\mathrm{ref} is a reference sound pressure. Commonly used reference sound pressures, defined in the standard ANSI S1.1-1994, are 20 µPa in air and 1 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 matches 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.

See also[edit]

References[edit]

  1. ^ Fundamentals of Telephone Communication Systems. Western Electric Company. 1969. p. 2.1. 
  2. ^ ANSI S1.1-1994. American National Standard: Acoustic Terminology. Sec 3.03.
  3. ^ Acoustical Society of America. "PACS 2010 Regular Edition—Acoustics Appendix". Retrieved 22 May 2013. 
  4. ^ a b "The Propagation of sound". Retrieved 26 June 2015. 
  5. ^ "What Does Sound Look Like?". NPR. YouTube. Retrieved 9 April 2014. 
  6. ^ Ensign, John Gay (19 August 2007). "Astronomy Picture of the Day". Retrieved 26 June 2015. 
  7. ^ a b Olson, Harry F. Autor (1967). Music, Physics and Engineering. p. 249. ISBN 9780486217697. 
  8. ^ "The American Heritage Dictionary of the English Language" (Fourth ed.). Houghton Mifflin Company. 2000. Archived from the original on June 25, 2008. Retrieved May 20, 2010. 

External links[edit]

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