NationMaster - Encyclopedia: Sound pressure

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 P_ac
Sound power level (SWL)
Sound energy density E
Sound energy flux q
Acoustic impedance Z
Speed of sound c

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 (symbol: Pa). The instantaneous sound pressure is the deviation from the local ambient pressure p₀ 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 over a given interval of time. In a sound wave, the complementary variable to sound pressure is the 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 medium. The local instantaneous sound intensity is the product of the sound pressure and the acoustic particle velocity and is, therefore, a vector quantity. It has been suggested that this article or section be merged into Sound pressure. ... 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. ... Sound is a vibration that travels through an elastic medium as a wave. ... The use of water pressure - the Captain Cook Memorial Jet in Lake Burley Griffin in Canberra, Australia. ... Sound is a disturbance of mechanical energy that propagates through matter as a wave. ... A wave is a disturbance that propagates through space or spacetime, transferring energy and momentum and sometimes angular momentum. ... A microphone, sometimes referred to as a mike or mic (both IPA pronunciation: ), is an acoustic to electric transducer or sensor that converts sound into an electrical signal. ... A hydrophone is a sound-to-electricity transducer for use in water or other liquids, analogous to a microphone for air. ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... In mathematics, the root mean square or rms is a statistical measure of the magnitude of a varying quantity. ... Particle velocity is the velocity v of a particle (real or imagined) in a medium as it transmits a wave. ... 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. ... 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. ... 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. ...

The sound pressure deviation p is

$p = frac{F}{A} ,$

where

F = force,

A = area.

The entire pressure p_total is

$p_mathrm{total} = p_0 + p ,$

where

p₀ = local ambient pressure,

p = sound pressure deviation.

1 Sound pressure level
- 1.1 Measuring sound pressure levels
- 1.2 Examples of sound pressure and sound pressure levels
2 See also
3 References
4 External links

Sound pressure level

Sound pressure level (SPL) or sound level L_p is a logarithmic measure of the rms sound pressure of a sound relative to a reference value. It is measured in decibels (dB (SPL), dBSPL, or dB_SPL). Sound is a disturbance of mechanical energy that propagates through matter as a wave. ... Look up level in Wiktionary, the free dictionary. ... A logarithmic scale is a scale of measurement that uses the logarithm of a physical quantity instead of the quantity itself. ... In mathematics, the root mean square or rms is a statistical measure of the magnitude of a varying quantity. ... The use of water pressure - the Captain Cook Memorial Jet in Lake Burley Griffin in Canberra, Australia. ... The decibel is a dimensionless unit (like percent) that is a measure of ratios on a logarithmic scale. ...

$L_p=10 log_{10}left(frac{p^2_{rms}}{p^2_0}right) =20 log_{10}left(frac{p_{rms}}{p_0}right)mbox{ dB} ,$

where $p 0$ is the reference sound pressure and $p r m s$ is the rms sound pressure being measured.

The commonly used reference sound pressure in air is p₀ = 20 µPa (rms). In underwater acoustics, the reference sound pressure is p₀ = 1 µPa (rms). The pascal (symbol: Pa) is the SI unit of pressure. ...

It can be useful to express sound pressure in this way when dealing with hearing, as the perceived loudness of a sound correlates roughly logarithmically to its sound pressure. See also Weber-Fechner law. Hearing is one of the traditional five senses, and refers to the ability to detect sound. ... The Weber - Fechner law attempts to describe the relationship between the physical magnitudes of stimuli and human perception of the intensity of stimuli. ...

Measuring sound pressure levels

dBSPL: A measurement of sound pressure level in decibels, where 0 dBSPL is the reference to the threshold of hearing. Often the calibration is done for 1 pascal is equal to 94 dBSPL. Fig. ...

When making measurements in air (and other gases), SPL is almost always expressed in decibels compared to a reference sound pressure of 20 µPa, which is usually considered the threshold of human hearing (roughly the sound of a mosquito flying 3 m away). Thus, most measurements of audio equipment will be made relative to this level. However, in other media, such as underwater, a reference level of 1 µPa is more often used.^[1] These references are defined in ANSI S1.1-1994.^[2] In general, it is necessary to know the reference level when comparing measurements of SPL. The unit dB (SPL) is often abbreviated to just "dB", which gives some the erroneous notion that a dB is an absolute unit by itself. The decibel (dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power) relative to a specified or implied reference level. ... Threshold of hearing is the sound pressure level SPL of 20 µPa (micropascals) = 2 × 10-5 pascal (Pa). ... Underwater acoustics is the study of the propagation of sound in water and the interaction of the mechanical waves that constitute sound with the water and its boundaries. ... The American National Standards Institute (ANSI) is a private, non-profit standards organization that produces industrial standards in the United States. ...

The human ear is a sound pressure sensitive detector. It does not have a flat spectral response, so the sound pressure is often frequency weighted such that the measured level will match the perceived level. When weighted in this way the measurement is referred to as a sound level. The International Electrotechnical Commission (IEC) has defined several weighting schemes. A-weighting attempts to match the response of the human ear to pure tones, while C-weighting is used to measure peak sound levels.^[3] If the (unweighted) SPL is desired, many instruments allow a "flat" or unweighted measurement to be made. See also Weighting filter. The ear is the sense organ that detects sounds. ... FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. ... Sound pressure level (SPL) or sound level Lp is a logarithmic measure of the energy of a particular noise relative to a reference noise source. ... 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. ... It has been suggested that this article or section be merged with A-weighting. ...

When measuring the sound created by an object, it is important to measure the distance from the object as well, since the SPL decreases in distance from a point source with 1/r (and not with 1/r², like sound intensity). It often varies in direction from the source, as well, so many measurements may be necessary, depending on the situation. An obvious example of a source that varies in level in different directions is a bullhorn. Look up point source in Wiktionary, the free dictionary. ... This diagram shows how the law works. ... 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. ... A megaphone is a cone-shaped device designed to amplify sound. ...

Sound pressure p in N/m² or Pa is

$p = Zv = frac{J}{v} = sqrt{JZ} ,$

where

Z is acoustic impedance, sound impedance, or characteristic impedance, in Pa·s/m

v is particle velocity in m/s

J is acoustic intensity or sound intensity, in W/m²

Sound pressure p is connected to particle displacement (or particle amplitude) ξ, in m, by 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. ... Acoustic impedance Z (characteristic impedance or sound impedance) is the ratio of sound pressure p to particle velocity v. ... The characteristic impedance of a uniform transmission line is the ratio of the amplitudes of a single pair of voltage and current waves propagating along the line in the absence of reflections. ... Particle velocity is the velocity v of a particle (real or imagined) in a medium as it transmits a wave. ... The sound intensity, J, (acoustic intensity) is defined as the sound power Pac per unit area A. The usual context is the measurement of sound intensity in the air at a listeners location. ... 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. ... 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. ...

$&# 0;= frac{v}{2 pi f} = frac{v}{omega} = frac{p}{Z omega} = frac{p}{ 2 pi f Z} ,$ .

Sound pressure p is

$p = rho c omega &# 0;= Z omega &# 0;= { 2 pi f &# 0;Z} = frac{a Z}{omega} = c sqrt{rho E} = sqrt{frac{P_{ac} Z}{A}} ,$ ,

normally in units of N/m² = Pa.

where:

Symbol	SI Unit	Meaning
p	pascals	sound pressure
f	hertz	frequency
ρ	kg/m³	density of air
c	m/s	speed of sound
v	m/s	particle velocity
$ω$ = 2 · $π$ · f	radians/s	angular frequency
ξ	meters	particle displacement
Z = c • ρ	N·s/m³	acoustic impedance
a	m/s²	particle acceleration
J	W/m²	sound intensity
E	W·s/m³	sound energy density
P_ac	watts	sound power or acoustic power
A	m²	Area

The distance law for the sound pressure p is inverse-proportional to the distance r of a punctual sound source. The International System of Units (symbol: SI) (for the French phrase Système International dUnités) is the most widely used system of units. ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... MHZ redirects here. ... FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. ... The U.S. National Prototype Kilogram, which currently serves as the primary standard for measuring mass in the U.S. It was assigned to the United States in 1889 and is periodically recertified and traceable to the primary international standard, The Kilogram, held at the Bureau International des Poids et... The metre (American English:meter) is a measure of length. ... The density of air, Ï (Greek: rho) (air density), is the mass per unit volume of Earths atmosphere, and is a useful value in aeronautics. ... The metre (American English:meter) is a measure of length. ... Look up second in Wiktionary, the free dictionary. ... Sound is a vibration that travels through an elastic medium as a wave. ... 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. ... Particle velocity is the velocity v of a particle (real or imagined) in a medium as it transmits a wave. ... In mathematics and physics, the radian is a unit of angle measure. ... Look up second in Wiktionary, the free dictionary. ... It has been suggested that this article or section be merged into Angular velocity. ... The metre, or meter (symbol: m) is the SI base unit of length. ... 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 newton (symbol: N) is the SI unit of force. ... Look up second in Wiktionary, the free dictionary. ... The metre (American English:meter) is a measure of length. ... 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. ... The metre (American English:meter) is a measure of length. ... Look up second in Wiktionary, the free dictionary. ... In a compressible sound transmission medium - mainly air - air particles get an accelerated motion: the particle acceleration or sound acceleration with the symbol a in metre/secondÂ². In acoustics or physics, acceleration (symbol: a) is defined as the rate of change (or time derivative) of velocity. ... The watt (symbol: W) is the SI derived unit of power, equal to one joule per second. ... The metre (American English:meter) is a measure of length. ... 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. ... The watt (symbol: W) is the SI derived unit of power, equal to one joule per second. ... Look up second in Wiktionary, the free dictionary. ... The metre (American English:meter) is a measure of length. ... 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 watt (symbol: W) is the SI derived unit of power, equal to one joule per second. ... Sound power or acoustic power Pac is a measure of sonic energy E per time t unit. ... Sound power or acoustic power is a measure of sonic energy E per time t unit. ... The metre (American English:meter) is a measure of length. ... Area is a physical quantity expressing the size of a part of a surface. ...

$p propto frac{1}{r} ,$ (proportional)

$frac{p_1} {p_2} = frac{r_2}{r_1} ,$

$p_1 = p_{2} cdot r_{2} cdot frac{1}{r_1} ,$

The assumption of 1/r² with the square is here wrong. That is only correct for sound intensity. 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. ...

Note: The often used term "intensity of sound pressure" is not correct. Use "magnitude", "strength", "amplitude", or "level" instead. "Sound intensity" is sound power per unit area, while "pressure" is a measure of force per unit area. Intensity is not equivalent to pressure. The magnitude of a mathematical object is its size: a property by which it can be larger or smaller than other objects of the same kind; in technical terms, an ordering of the class of objects to which it belongs. ... Amplitude is a nonnegative scalar measure of a waves magnitude of oscillation, that is, magnitude of the maximum disturbance in the medium during one wave cycle. ... Look up level in Wiktionary, the free dictionary. ... 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 power or acoustic power Pac is a measure of sonic energy E per time t unit. ...

$I sim {p^2} sim dfrac{1}{r^2} ,$

Hence $p sim dfrac{1}{r} ,$

Examples of sound pressure and sound pressure levels

This article does not cite any references or sources.
Please help improve this article by adding citations to reliable sources. (help, get involved!)
Unverifiable material may be challenged and removed.
This article has been tagged since March 2007.

Source of sound	Sound pressure	Sound pressure level^[4]
	pascal	dB SPL
Theoretical limit for a sound wave at 1 atmosphere environmental pressure	101,325 Pa	194 dB
Krakatoa explosion at 100 miles (160 km) in air	20,000 Pa	[1] 180 dB
Simple open-ended thermoacoustic device ^[5]	12,000 Pa	176 dB
M1 Garand being fired at 1 m	5,000 Pa	168 dB
Jet engine at 30 m	630 Pa	150 dB
Rifle being fired at 1 m	200 Pa	140 dB
Threshold of pain	100 Pa	130 dB
Hearing damage (due to short-term exposure)	20 Pa	approx. 120 dB
Jet at 100 m	6 – 200 Pa	110 – 140 dB
Jack hammer at 1 m	2 Pa	approx. 100 dB
Hearing damage (due to long-term exposure)	6×10⁻¹ Pa	approx. 85 dB
Major road at 10 m	2×10⁻¹ – 6×10⁻¹ Pa	80 – 90 dB
Passenger car at 10 m	2×10⁻² – 2×10⁻¹ Pa	60 – 80 dB
TV (set at home level) at 1 m	2×10⁻² Pa	approx. 60 dB
Normal talking at 1 m	2×10⁻³ – 2×10⁻² Pa	40 – 60 dB
Very calm room	2×10⁻⁴ – 6×10⁻⁴ Pa	20 – 30 dB
Leaves rustling, calm breathing	6×10⁻⁵ Pa	10 dB
Auditory threshold at 2 kHz	2×10⁻⁵ Pa	0 dB

The formula for the sum of the sound pressure levels of n incoherent radiating sources is The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... It has been suggested that this article or section be merged into sound pressure level. ... Standard atmosphere (symbol: atm) is a unit of pressure. ... The use of water pressure - the Captain Cook Memorial Jet in Lake Burley Griffin in Canberra, Australia. ... Krakatoa or Krakatau or Krakatao is a volcanic island in the Sunda Strait between Java and Sumatra in Indonesia. ... Sonic or thermoacoustic refrigeration is a technology that uses high-amplitude sound waves in a pressurised gas to pump heat from one place to another. ... The M1 Garand (more formally the United States Rifle, Caliber . ... 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. ... The metre (American English:meter) is a measure of length. ... This article does not cite any references or sources. ... Fig. ... Please wikify (format) this article or section as suggested in the Guide to layout and the Manual of Style. ... Look up jet in Wiktionary, the free dictionary. ... The word jackhammer is also used in the name of the type of combat shotgun called the Pancor Jackhammer. ... Please wikify (format) this article or section as suggested in the Guide to layout and the Manual of Style. ... Restored passenger cars on display at the Mid-Continent Railway Museum in North Freedom, WI. A passenger car is a piece of railroad rolling stock that is designed to carry passengers. ... Threshold of hearing is the sound pressure level SPL of 20 µPa (micropascal) = 2 × 10-5 Pascal (Pa). ...

$L_Sigma = 10,cdot,{rm log}_{10} left(frac{p_1^2 + p_2^2 + cdots + p_n^2}{p_0^2}right) = 10,cdot,{rm log}_{10} left(left({frac{p_1}{p_0}}right)^2 + left({frac{p_2}{p_0}}right)^2 + cdots + left({frac{p_n}{p_0}}right)^2right)$

From the formula of the sound pressure level we find

$left({frac{p_i}{p_0}}right)^2 = 10^{frac{L_i}{10}},qquad i=1,2,cdots,n$

This inserted in the formula for the sound pressure level to calculate the sum level shows

$L_Sigma = 10,cdot,{rm log}_{10} left(10^{frac{L_1}{10}} + 10^{frac{L_2}{10}} + cdots + 10^{frac{L_n}{10}} right),{rm dB}$

References

Beranek, Leo L, "Acoustics" (1993) Acoustical Society of America. ISBN 0-88318-494-X
Morfey, Christopher L, "Dictionary of Acoustics" (2001) Academic Press, San Diego.

External links

Conversion of sound pressure to sound pressure level and vice versa
The level of sound is dB
Table of Sound Levels - Corresponding Sound Pressure and Sound Intensity
SPL of many different sounds - txt
Ohm's law as acoustic equivalent - calculations
Definition of sound pressure level
A table of SPL values
Relationships of acoustic quantities associated with a plane progressive acoustic sound wave - pdf
Another Sound Pressure Level Decibel Table
Sound pressure and sound power - two commonly confused characteristics of sound

Categories: Sound measurements | Articles lacking sources from March 2007 | All articles lacking sources

Results from FactBites:

YouTube - The Pressure Sounds - Beautiful Day (385 words)
	But The Pressure Sounds are clean and refined Skanin' Band!
	The Pressure Sounds from Washington DC performing "Beautiful Day".
	The Pressure Sounds Washington DC ska rocksteady Checkered Cabs Caz Gardiner dcska

Browse by Label: PRESSURE SOUNDS (UK) (2286 words)
	They are both very different and the first, showcased on the first Pressure Sounds release An Even Harder Shade Of Black and now continued with this release, dates from between 1973 and 1975 when Leonard was at the centre of Kingston's musical maelstrom.
	Here on the first release by Pressure Sounds in the new century is a collection of his finest work.
	Prince Jazzbo was born in Clarendon, Jamaica in 1951.

More results at FactBites »

COMMENTARY

Share your thoughts, questions and commentary here

Want to know more?
Search encyclopedia, statistics and forums:

Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms.

Contents

Sound pressure level GA_googleFillSlot("encyclopedia_square");

Measuring sound pressure levels

Examples of sound pressure and sound pressure levels

See also

References

External links

Sound pressure level