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Encyclopedia > Sound

## Physics of sound

The mechanical vibrations that can be interpreted as sound can travel through all forms of matter: gases, liquids, solids, and plasmas. However, sound cannot propagate through vacuum. The matter that supports the sound is called the medium. In the physical sciences, a state of matter is one of the many ways that matter can interact with itself to form a macroscopic, homogenous phase. ... Gas phase particles (atoms, molecules, or ions) move around freely Gas is one of the four major states of matter, consisting of freely moving atoms or molecules without a definite shape and without a definite volume. ... For other uses, see Liquid (disambiguation). ... This box:      For other uses, see Solid (disambiguation). ... For other uses, see Plasma. ... Look up Vacuum in Wiktionary, the free dictionary. ... A transmission medium is any material substance, such as fiber-optic cable, twisted-wire pair, coaxial cable, dielectric-slab waveguide, water, or air, that can be used for the propagation of signals, usually in the form of modulated radio, light, or acoustic waves, from one point to another. ...

### Longitudinal and transverse waves

Sound is transmitted through gases, plasma, and liquids as longitudinal waves, also called compression waves. Through solids, however, it can be transmitted as both longitudinal 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. Longitudinal waves are waves that have vibrations along or parallel to their direction of travel. ... Bold text Wiktionary has related dictionary definitions, such as: compressor, compression inthe wkjhrlfidhb;g/df == Compressor may refer to: Gas compressor, a mechanical device that compresses a gas e. ... Longitudinal waves are waves that have vibrations along or parallel to their direction of travel. ... A light wave is an example of a transverse wave. ... This article is about pressure in the physical sciences. ... Look up equilibrium in Wiktionary, the free dictionary. ... Physical compression is the result of the subjection of a material to compressive stress, resulting in reduction of volume. ... Rarefaction is the reduction of a mediums density, or the opposite of compression. ... A light wave is an example of a transverse wave. ... Shear stress is a stress state where the stress is parallel or tangential to a face of the material, as opposed to normal stress when the stress is perpendicular to the face. ...

Matter in the medium is periodically displaced by a sound wave, and thus oscillates. The energy carried by the sound wave is split equally between the potential energy of the extra compression (in case of longitudinal waves) or strain (in case of transverse waves) of the matter and the kinetic energy of the oscillations of the medium. Physical compression is the result of the subjection of a material to compressive stress, resulting in reduction of volume. ... This article is about the deformation of materials. ...

### Sound wave properties and characteristics

Transverse waves, also known as shear waves, have an additional property of polarization. A light wave is an example of a transverse wave. ... Shear stress is a stress state where the stress is parallel or tangential to a face of the material, as opposed to normal stress when the stress is perpendicular to the face. ... In electrodynamics, polarization (also spelled polarisation) is the property of electromagnetic waves, such as light, that describes the direction of their transverse electric field. ...

Sound characteristics can depend on the type of sound waves (longitudinal versus transverse) as well as on the physical properties of the transmission medium. 1) A physical property is an aspect of an object that can be experienced using one of the five human senses: touch, taste, smell, sight or sound, or, in an extended sense, detected through any measuring device. ...

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. Pitch may refer to: Look up Pitch in Wiktionary, the free dictionary. ... For other uses, see Frequency (disambiguation). ... It has been suggested that pulse amplitude be merged into this article or section. ...

### Acoustics and noise

The scientific study of the propagation, absorption, and reflection of sound waves is called acoustics. Acoustics is the branch of physics concerned with the study of sound (mechanical waves in gases, liquids, and solids). ...

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. This article is about noise as in sound. ...

## Speed of sound

Main article: 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 air at sea level, the speed of sound is approximately 343 m/s, in fresh water 1482 m/s (both at 20 °C, or 68 °F), and in steel about 5960 m/s.[2] 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). This page is about the physical speed of sound waves in a medium. ... An elastic modulus, or modulus of elasticity, is the mathematical description of an object or substances tendency to be deformed when a force is applied to it. ... For other uses, see Density (disambiguation). ... For other uses, see Temperature (disambiguation). ... Metre per second (U.S. spelling: meter per second) is an SI derived unit of both speed (scalar) and velocity (vector), defined by distance in metres divided by time in seconds. ... The parametric array is a nonlinear transduction mechanism that generates narrow, nearly sidelobe free beams of low frequency sound, through the mixing and interaction of high frequency sound waves, effectively overcoming the diffraction limit (a kind of spatial uncertainty principle) associated with linear acoustics [1]. Parametric arrays can be formed...

## Sound pressure level

Main article: Sound pressure
Sound measurements
Sound pressure p
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
v  d  e

Sound pressure is defined as the difference between the actual pressure (at a given point and a given time) in the medium and the average, or equilibrium, pressure of the medium at that location. 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 Pa RMS sound pressure 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. Such a tiny (relative to atmospheric) variation in air pressure at an audio frequency will be perceived as quite a deafening sound, and can cause hearing damage, according to the table below. Sound pressure is the pressure deviation from the local ambient pressure caused by a sound wave. ... Sound pressure is the pressure deviation from the local ambient pressure caused by a sound wave. ... Particle velocity is the velocity v of a particle (real or imagined) in a medium as it transmits a wave. ... The particle velocity level or the sound velocity level tells the ratio of a sound incidence in comparison to a reference level of 0 dB. It shows the ratio of the particle velocity v1 and the particle velocity v0. ... Particle displacement or particle amplitude (represented in mathematics by the lower-case Greek letter Î¾) is a measurement of distance (in metres) of the movement of a particle in a medium as it transmits a wave. ... The sound intensity, I, (acoustic intensity) is defined as the sound power Pac per unit area A. The usual context is the noise measurement of sound intensity in the air at a listeners location. ... Sound intensity level or acoustic intensity level is a logarithmic measure of the sound intensity in comparison to the reference level of 0 dB (decibels). ... Sound power or acoustic power Pac is a measure of sonic energy E per time t unit. ... Sound power level or acoustic power level is a logarithmic measure of the sound power in comparison to a specified reference level. ... The sound energy density or sound density (symbol E or w) is an adequate measure to describe the sound field at a given point as a sound energy value. ... The sound energy flux is the average rate of flow of sound energy for one period through any specified area. ... The acoustic impedance Z (or sound impedance) is a frequency f dependent parameter and is very useful, for example, for describing the behaviour of musical wind instruments. ... This page is about the physical speed of sound waves in a medium. ... In mathematics, the root mean square or rms is a statistical measure of the magnitude of a varying quantity. ... For other uses, see Pascal. ... An audio frequency (abbreviation: AF) is any frequency from about 20 hertz to about 20 kilohertz, which is the approximate range of sound frequencies that is audible to humans. ... The word deaf can have very different meanings depending on the background of the person speaking or the context in which the word is used. ...

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 Lp is defined as For other uses, see Decibel (disambiguation). ...

$L_mathrm{p}=10, log_{10}left(frac{{p}^2}{{p_mathrm{ref}}^2}right) =20, log_{10}left(frac{p}{p_mathrm{ref}}right)mbox{ dB}$
where p is the root-mean-square sound pressure and pref 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 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. In mathematics, root mean square (abbreviated RMS or rms), also known as the quadratic mean, is a statistical measure of the magnitude of a varying quantity. ... The American National Standards Institute or ANSI (pronounced an-see) is a nonprofit organization that oversees the development of standards for products, services, processes and systems in the United States. ... The pascal (symbol: Pa) is the SI unit of pressure. ... The pascal (symbol: Pa) is the SI unit of pressure. ... For other uses, see Ear (disambiguation). ... For other uses, see Frequency (disambiguation). ... The International Electrotechnical Commission (IEC) is an international standards organization dealing with electrical, electronic and related technologies. ... The A-weighting curve is one of a family of curves defined in IEC179 and various other standards for use in sound level meters. ...

### Examples of sound pressure and sound pressure levels

Source of sound RMS sound pressure sound pressure level
Pa dB re 20 µPa
Nuclear Weapon explosion approx 248
1883 Krakatoa eruption approx 180
rocket launch equipment acoustic tests approx. 165
threshold of pain 100 134
hearing damage during short-term effect 20 approx. 120
jet engine, 100 m distant 6–200 110–140
jackhammer, 1 m distant / discotheque 2 approx. 100
hearing damage from long-term exposure 0.6 approx. 85
traffic noise on major road, 10 m distant 0.2–0.6 80–90
moving automobile, 10 m distant 0.02–0.2 60–80
TV set – typical home level, 1 m distant 0.02 approx. 60
normal talking, 1 m distant 0.002–0.02 40–60
very calm room 0.0002–0.0006 20–30
quiet rustling leaves, calm human breathing 0.00006 10
auditory threshold at 2 kHz – undamaged human ears 0.00002 0

In mathematics, the root mean square or rms is a statistical measure of the magnitude of a varying quantity. ... For other uses, see Pascal. ... For other uses, see Decibel (disambiguation). ... The mushroom cloud of the atomic bombing of Nagasaki, Japan, 1945, rose some 18 kilometers (11 mi) above the hypocenter A nuclear weapon derives its destructive force from nuclear reactions of fusion or fission. ... For the 1969 film about the Krakatoa eruption, see Krakatoa, East of Java. ... Fig. ... A Pratt and Whitney turbofan engine for the F-15 Eagle is tested at Robins Air Force Base, Georgia, USA. The tunnel behind the engine muffles noise and allows exhaust to escape. ... This article is about the construction tool. ... Discothèque redirects here. ... Please wikify (format) this article or section as suggested in the Guide to layout and the Manual of Style. ... Car redirects here. ... Threshold of hearing is the sound pressure level SPL of 20 µPa (micropascal) = 2 × 10-5 Pascal (Pa). ...

## Equipment for dealing with sound

Equipment for generating or using sound includes musical instruments, hearing aids, sonar systems and sound reproduction and broadcasting equipment. Many of these use electro-acoustic transducers such as microphones and loudspeakers. A musical instrument is a device constructed or modified with the purpose of making music. ... Behind the ear aid For the song, see Flood (album). ... This article is about underwater sound propagation. ... Sound reproduction is the electrical or mechanical re-creation and/or amplification of sound, often as music. ... Microphones redirects here. ... For the Marty Friedman album, see Loudspeaker (album) An inexpensive low fidelity 3. ...

## References

1. ^ Strutt (Rayleigh), J W; Lindsay, R B (1877). The Theory of Sound. Dover Publications. ISBN 0-4866-0292-3.
2. ^ The Soundry: The Physics of Sound

See also Rayleigh fading Rayleigh scattering Rayleigh number Rayleigh waves Rayleigh-Jeans law External links Nobel website bio of Rayleigh About John William Strutt MacTutor biography of Lord Rayleigh Categories: People stubs | 1842 births | 1919 deaths | Nobel Prize in Physics winners | Peers | British physicists | Discoverer of a chemical element ...

## Sound measurement

Results from FactBites:

 Sound and Vision Magazine - Home Theater Equipment, Audio and Video Equipment, Plasma and LCD HDTVs, HD-DVD vs Blu-Ray (270 words) When a New York City landmark needed an innovative new sound system, Definitive Technology came to the rescue. Sound and Vision's expert reviewers recommend the best gear to buy right now. Let Sound and Vision help you find the best equipment for your home, taste, and budget.
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