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{{CogPsy}} 

{{Sound measurements}} 

{{Sound measurements}} 




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==Sound pressure== 
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{{Sound measurements}} 

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'''Sound pressure''' is the local [[pressure]] deviation from the ambient (average, or equilibrium) 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 ''p''<sub>0</sub> 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 (or space). In a sound wave, the complementary variable to sound pressure is the [[particle velocityacoustic 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 mediummedium]]. The local instantaneous [[sound intensity]] is the product of the sound pressure and the acoustic particle velocity and is, therefore, a vector quantity. 




− 
'''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 ''p''<sub>0</sub> 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 [[particle velocityacoustic 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 partical velocity and is, therefore, a vector quantity. 
+ 
The sound pressure deviation ''p'' is 
− 


− 
The sound pressure deviation ''p'' is: 


:<math> 

:<math> 
− 
p = \frac{F}{A} 
+ 
p = \frac{F}{A} \, 

</math> 

</math> 
− 
F = force<br> 

− 
A = area 





− 
The entire pressure '' p<sub>total</sub> is: 
+ 
where 
− 
:<math>p_{total} = p_0 + p \, 
+ 
:''F'' = force, 

+ 
:''A'' = area. 

+ 


+ 
The entire pressure ''p''<sub>total</sub> is 

+ 
:<math> 

+ 
p_\mathrm{total} = p_0 + p \, 

</math> 

</math> 
− 
''p''<sub>0</sub> = local ambient pressure<br> 
+ 

− 
''p'' = sound pressure deviation 
+ 
where 

+ 
:''p''<sub>0</sub> = local ambient pressure, 

+ 
:''p'' = sound pressure deviation. 





==Sound pressure level== 

==Sound pressure level== 
− 
'''Sound pressure level''' (SPL) or sound level ''L''<sub>p</sub> is a [[logarithmic scalelogarithmic measure]] of the [[rms]] [[pressure]] (force/area) of a particular noise relative to a reference noise source. It is usually measured in [[decibels]] ('''dB (SPL)''', '''dBSPL''', or '''dB<sub>SPL</sub>'''). 
+ 
'''Sound pressure level''' (SPL) or [[sound]] [[level]] ''L''<sub>p</sub> is a [[logarithmic scalelogarithmic measure]] of the [[root mean squarerms]] sound [[pressure]] of a sound relative to a reference value. It is measured in [[decibels]] (dB). Sometimes variants are used such as dB (SPL), dBSPL, or dB<sub>SPL</sub>. These variants are not permitted by [[SI]]. 

:<math> 

:<math> 
− 
L_\mathrm{p}=10\, \log_{10}\left(\frac{{p}^2}{{p_0}^2}\right) =20\, \log_{10}\left(\frac{p}{p_0}\right)\mbox{ dB} 
+ 
L_p=10 \log_{10}\left(\frac{p^2_{\mathrm{{rms}}}}{p^2_{\mathrm{ref}}}\right) =20 \log_{10}\left(\frac{p_{\mathrm{rms}}}{p_{\mathrm{ref}}}\right)\mbox{ dB} \, 

</math> 

</math> 

+ 
where <math>p_{\mathrm{ref}}</math> is the reference sound pressure and <math>p_{\mathrm{rms}}</math> is the rms sound pressure being measured.<ref>Sometimes reference sound pressure is denoted ''p''<sub>0</sub>, not to be confused with the (much higher) ambient pressure.</ref> 




− 
:where ''p''<sub>0</sub> is the reference [[sound pressure]] and ''p'' is the [[rootmeansquare]] sound pressure being measured. 
+ 
The commonly used reference sound pressure in air is <math>p_{\mathrm{ref}}</math> = 20 [[micropascalµPa]] (rms). In underwater acoustics, the reference sound pressure is <math>p_{\mathrm{ref}}</math> = 1 µPa (rms). 




− 
The commonly used reference sound pressure in air is ''p''<sub>0</sub> = 20 [[micropascalµPa]] ([[rootmeansquare]]). 
+ 
It can be useful to express sound pressure in this way when dealing with [[hearing (sense)hearing]], as the perceived loudness of a sound correlates roughly logarithmically to its sound pressure. ''See also [[WeberFechner law]].'' 
− 


− 
It can be useful to express sound pressure in this way when dealing with [[hearing (sense)hearing]], as the perceived loudness of a sound correlates roughly logarithmically to its sound pressure. ''See also [[WeberFechner law]].'' 






=== Measuring sound pressure levels === 

=== Measuring sound pressure levels === 
− 
When making measurements in air (and other gases), SPL is almost always expressed in [[decibel]]s compared to a reference sound pressure of 20 µPa ([[pascalmicropascals]]), which is usually considered the [[threshold of human hearing]] (roughly the sound of a mosquito flying 3 metres away). Thus, most measurements of audio equipment will be made relative to this level. However, in other media, such as [[underwater acousticsunderwater]], a reference level of 1 µPa is more often used. <ref>[http://www.fas.org/man/dod101/sys/ship/acoustics.htm Underwater Acoustics] — Federation of American Scientists</ref> These references are defined in [[ANSI]] S1.11994. <ref>[http://www.quietnoise.com/glossary.htm Glossary of Noise Terms] — ''Sound pressure level'' definition</ref> 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. 
+ 
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. 

+ 


+ 
When making measurements in air (and other gases), SPL is almost always expressed in [[decibel]]s 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 acousticsunderwater]], a reference level of 1 µPa is more often used.<ref name="Morfey">C. L. Morfey, Dictionary of Acoustics (Academic Press, San Diego, 2001).</Ref> These references are defined in [[American National Standards InstituteANSI]] S1.11994.<ref>[http://www.quietnoise.com/glossary.htm Glossary of Noise Terms] — ''Sound pressure level'' definition</ref> 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. 




− 
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 sound level. The [[International Electrotechnical Commission]] (IEC) has defined several weighting schemes. [[Aweighting]] attempts to match the response of the human ear to noise, while Cweighting is used to measure peak sound levels. <ref>[http://www.cirrusresearch.co.uk/glossary.html Glossary of Terms] — Cirrus Research plc.</ref> If the actual, as opposed to weighted, SPL is desired, many instruments allow a "flat" or unweighted measurement to be made. ''See also [[Weighting filter]].'' 
+ 
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. [[Aweighting]] attempts to match the response of the human ear to pure tones, while Cweighting is used to measure peak sound levels.<ref>[http://www.cirrusresearch.co.uk/glossary.html Glossary of Terms] — Cirrus Research plc.</ref> If the (unweighted) SPL is desired, many instruments allow a "flat" or unweighted measurement to be made. ''See also [[Weighting filter]].'' 




− 
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 [[Inversesquare law1/r<sup>2</sub>]], 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]].) 
+ 
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 [[Inversesquare law1/''r''<sup>2</sub>]], 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]]. 




− 
Sound pressure ''p'' in N/m<sup>2</sup> or Pa is: 
+ 
Sound pressure ''p'' in N/m² or Pa is 

:<math> 

:<math> 
− 
p = Zv = \frac{J}{v} = \sqrt{JZ} 
+ 
p = Zv = \frac{J}{v} = \sqrt{JZ} \, 

</math> 

</math> 




− 
: ''Z'': [[acoustic impedance]], [[sound impedance]], or [[characteristic impedance]], in Pa·s/m 
+ 
where 
− 
: ''v'': [[particle velocity]] in m/s 
+ 
: ''Z'' is [[acoustic impedance]], [[sound impedance]], or [[characteristic impedance]], in Pa·s/m 
− 
: ''J'': [[acoustic intensity]] or [[sound intensity]], in W/m<sup>2</sup> 
+ 
: ''v'' is [[particle velocity]] in m/s 

+ 
: ''J'' is [[acoustic intensity]] or [[sound intensity]], in W/m<sup>2</sup> 




− 
Sound pressure ''p'' is connected to '''[[particle displacement]]''' (or particle amplitude) ξ, in m, by: 
+ 
Sound pressure ''p'' is connected to '''[[particle displacement]]''' (or particle amplitude) ξ, in m, by 

:<math> 

:<math> 
− 
\xi = \frac{v}{2 \pi f} = \frac{v}{\omega} = \frac{p}{Z \omega} = \frac{p}{ 2 \pi f Z} 
+ 
\xi = \frac{v}{2 \pi f} = \frac{v}{\omega} = \frac{p}{Z \omega} = \frac{p}{ 2 \pi f Z} \, 
− 
</math> 
+ 
</math>. 




− 
Sound pressure ''p'': 
+ 
Sound pressure ''p'' is 

:<math> 

:<math> 
− 
p = \rho c \omega \xi = Z \omega \xi = { 2 \pi f \xi Z} = \frac{a Z}{\omega} = c \sqrt{\rho E} = \sqrt{\frac{P_{ac} Z}{A}} 
+ 
p = \rho c \omega \xi = Z \omega \xi = { 2 \pi f \xi Z} = \frac{a Z}{\omega} = c \sqrt{\rho E} = \sqrt{\frac{P_{ac} Z}{A}} \, 
− 
</math> 
+ 
</math>, 
− 
normally in units of N/m<sup>2</sup> = Pa. 
+ 


+ 
normally in units of N/m² = Pa. 





where: 

where: 




− 
{ {{prettytable}} 
+ 
{ class="wikitable" 
− 
! Symbol !! Units !! Meaning 
+ 
! Symbol !! [[SI Unit]] !! Meaning 

 

 

! ''p'' 

! ''p'' 
− 
 [[pascals]]  [[sound pressure]] 
+ 
 [[pascal (unit)pascal]]s  sound pressure 

 

 

! ''f'' 

! ''f'' 

 [[hertz]]  [[frequency]] 

 [[hertz]]  [[frequency]] 

 

 
− 
! ''ρ'' 
+ 
! ''ρ'' 
− 
 [[kilogramkg]]/[[meterm]]<sup>3</sup>  [[density of air]] 
+ 
 [[kilogramkg]]/[[Metrem]]³  [[density of air]] 

 

 

! ''c'' 

! ''c'' 
− 
 [[meterm]]/[[seconds]]  [[speed of sound]] 
+ 
 [[Metrem]]/[[seconds]]  [[speed of sound]] 

 

 

! ''v'' 

! ''v'' 

 [[Meters per secondm/s]]  [[particle velocity]] 

 [[Meters per secondm/s]]  [[particle velocity]] 

 

 
− 
! <math>\omega</math> = 2 · <math>\pi</math> · ''f'' 
+ 
! <math>\omega</math> = 2 · <math>\pi</math> · ''f'' 

 [[radians]]/[[seconds]]  [[angular frequency]] 

 [[radians]]/[[seconds]]  [[angular frequency]] 

 

 
− 
! ''ξ'' 
+ 
! ''ξ'' 
− 
 [[meter]]s  [[Particle displacement]] 
+ 
 [[meter]]s  [[particle displacement]] 

 

 

! ''Z = c • ρ'' 

! ''Z = c • ρ'' 
− 
 [[NewtonN]]·[[seconds]]/[[Meterm]]³  [[acoustic impedance]] 
+ 
 [[NewtonN]]·[[seconds]]/[[Metrem]]³  [[acoustic impedance]] 

 

 

! ''a'' 

! ''a'' 
− 
 [[meterm]]/[[seconds]]²  [[Particle acceleration]] 
+ 
 [[Metrem]]/[[seconds]]²  [[particle acceleration]] 

 

 

! ''J'' 

! ''J'' 
− 
 [[WattW]]/[[Meterm]]²  [[sound intensity]] 
+ 
 [[WattW]]/[[Metrem]]²  [[sound intensity]] 

 

 

! ''E'' 

! ''E'' 
− 
 [[WattW]]·[[seconds]]/[[Meterm]]m³  [[sound energy density]] 
+ 
 [[WattW]]·[[seconds]]/[[Metrem]]³  [[sound energy density]] 

 

 

! ''P''<sub>ac</sub> 

! ''P''<sub>ac</sub> 
Line 95: 
Line 95: 

 

 

! ''A'' 

! ''A'' 
− 
 [[meterm]]²  [[Area]] 
+ 
 [[Metrem]]²  [[Area]] 

} 

} 





The '''distance law''' for the sound pressure ''p'' is inverseproportional to the distance ''r'' of a punctual sound source. 

The '''distance law''' for the sound pressure ''p'' is inverseproportional to the distance ''r'' of a punctual sound source. 

:<math> 

:<math> 
− 
p \propto \frac{1}{r} 
+ 
p \propto \frac{1}{r} \, 

</math> (proportional) 

</math> (proportional) 

+ 


:<math> 

:<math> 
− 
\frac{p_1} {p_2} = \frac{r_2}{r_1} 
+ 
\frac{p_1} {p_2} = \frac{r_2}{r_1} \, 

</math> 

</math> 

+ 


:<math> 

:<math> 
− 
p_1 = p_{2} \cdot r_{2} \cdot \frac{1}{r_1} 
+ 
p_1 = p_{2} \cdot r_{2} \cdot \frac{1}{r_1} \, 

</math> 

</math> 




− 
The assumption of 1/''r''² with the square is here wrong. Thats only right for [[sound intensity]]. 
+ 
The assumption of 1/''r''² with the square is here wrong. That is only correct for [[sound intensity]]. 




− 
''Note: The often used term "intensity of sound pressure" is not correct. Use "[[Magnitude (mathematics)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.'' 
+ 
''Note: The often used term "intensity of sound pressure" is not correct. Use "[[Magnitude (mathematics)magnitude]]", "[[wikt:strengthstrength]]", "[[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.'' 

+ 
:<math> 

+ 
I \sim {p^2} \sim \dfrac{1}{r^2} \, 

+ 
</math> 

+ 
Hence 

+ 
<math> 

+ 
p \sim \dfrac{1}{r} \, 

+ 
</math> 





=== Examples of sound pressure and sound pressure levels === 

=== Examples of sound pressure and sound pressure levels === 
− 

+ 
<! This section is linked from [[Sound]] > 

{ class="wikitable" 

{ class="wikitable" 
− 
! situation !! sound pressure (pascal) !! sound pressure level dB (SPL) 
+ 
! Source of sound !! Sound pressure !! Sound pressure level<ref> [http://www.makeitlouder.com/Decibel%20Level%20Chart.txt Decibel level chart.] </ref> 

 

 
− 
[[threshold of pain]]  align="right"  100 Pa  align="right"  134 dB 
+ 
!   !! [[pascal (unit)pascal]] !! [[dB SPL]] 

 

 
− 
hearing damage during short term effect  align="right"  20 Pa  align="right"  approx. 120 dB 
+ 
Theoretical limit for undistorted sound at<br>1 [[atmosphere (unit)atmosphere]] environmental [[pressure]]  align="right"  101,325 Pa  align="right" 194 dB 

 

 
− 
[[jet]], 100 m distant  align="right"  6 – 200 Pa  align="right"  110 – 140 dB 
+ 
[[Krakatoa]] explosion at 100 miles (160 km) in air  align="right"  20,000 Pa  align="right"  [http://www.makeitlouder.com/Decibel%20Level%20Chart.txt] 180 dB 

 

 
− 
[[jack hammer]], 1 m distant / [[discotheque]]  align="right"  2 Pa  align="right"  approx. 100 dB 
+ 
Simple openended [[thermoacousticsthermoacoustic device]] <ref>Hatazawa, M., Sugita, H., Ogawa, T. & Seo, Y. (Jan. 2004), ‘Performance of a thermoacoustic sound wave generator driven with waste heat of automobile gasoline engine,’ ''Transactions of the Japan Society of Mechanical Engineers (Part B)'' Vol. 16, No. 1, 292–299. 

+ 
[http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=200407211336MT&q=Performance+of+a+thermoacoustic+sound+wave+generator+driven+with+waste+heat+of+automobile+gasoline+engine&uid=790404233&setcookie=yes] 

+ 
</ref>  align="right"  12,000 Pa  align="right"  176 dB 

 

 
− 
[[hearing damage]] during longterm effect  align="right"  6×10<sup>−1</sup> Pa  align="right"  approx. 90 dB 
+ 
[[M1 Garand]] being fired at 1 m  align="right"  5,000 Pa  align="right"  168 dB 

 

 
− 
major road, 10 m distant  align="right"  2×10<sup>−1</sup> – 6×10<sup>−1</sup> Pa  align="right"  80 – 90 dB 
+ 
[[Jet engine]] at 30 [[metrem]]  align="right"  630 Pa  align="right"  150 dB 

 

 
− 
[[passenger car]], 10 m distant  align="right"  2×10<sup>−2</sup> – 2×10<sup>−1</sup> Pa  align="right"  60 – 80 dB 
+ 
[[Rifle]] being fired at 1 m  align="right"  200 Pa  align="right"  140 dB 

 

 
− 
TV set at home level, 1 m distant  align="right"  2×10<sup>−2</sup> Pa  align="right"  ca. 60 dB 
+ 
[[Threshold of pain]]  align="right"  100 Pa  align="right"  130 dB 

 

 
− 
normal talking, 1 m distant  align="right"  2×10<sup>−3</sup> – 2×10<sup>−2</sup> Pa  align="right"  40 – 60 dB 
+ 
[[Hearing damage]] (due to shortterm exposure)  align="right"  20 Pa  align="right"  approx. 120 dB 

 

 
− 
very calm room  align="right"  2×10<sup>−4</sup> – 6×10<sup>−4</sup> Pa  align="right"  20 – 30 dB 
+ 
[[Jet]] at 100 m  align="right"  6 – 200 Pa  align="right"  110 – 140 dB 

 

 
− 
leaves noise, calm breathing  align="right"  6×10<sup>−5</sup> Pa  align="right"  10 dB 
+ 
[[Jack hammer]] at 1 m  align="right"  2 Pa  align="right"  approx. 100 dB 

 

 
− 
[[auditory threshold]] at 2 kHz  align="right"  2×10<sup>−5</sup> Pa  align="right"  0 dB 
+ 
[[Hearing damage]] (due to longterm exposure)  align="right"  6×10<sup>−1</sup> Pa  align="right"  approx. 85 dB 

+ 
 

+ 
Major road at 10 m  align="right"  2×10<sup>−1</sup> – 6×10<sup>−1</sup> Pa  align="right"  80 – 90 dB 

+ 
 

+ 
[[Passenger car]] at 10 m  align="right"  2×10<sup>−2</sup> – 2×10<sup>−1</sup> Pa  align="right"  60 – 80 dB 

+ 
 

+ 
TV (set at home level) at 1 m  align="right"  2×10<sup>−2</sup> Pa  align="right"  approx. 60 dB 

+ 
 

+ 
Normal talking at 1 m  align="right"  2×10<sup>−3</sup> – 2×10<sup>−2</sup> Pa  align="right"  40 – 60 dB 

+ 
 

+ 
Very calm room  align="right"  2×10<sup>−4</sup> – 6×10<sup>−4</sup> Pa  align="right"  20 – 30 dB 

+ 
 

+ 
Leaves rustling, calm breathing  align="right"  6×10<sup>−5</sup> Pa  align="right"  10 dB 

+ 
 

+ 
[[Auditory threshold]] at 2 kHz  align="right"  2×10<sup>−5</sup> Pa  align="right"  0 dB 

} 

} 




− 
=== SPL in audio equipment === 
+ 
The formula for the sum of the sound pressure levels of ''n'' incoherent radiating sources is 
− 
Most audio manufacturers use SPL to describe the [[Electrical efficiencyefficiency]] of their speakers. The most common means is measuring the sound pressure level from the speaker with the measuring device placed directly in front of and one meter away from the source. Then a particular sound (usually [[white noise]] or [[pink noise]]) is played through the source at a particular intensity so that the source is consuming one watt of power. The SPL is then measured and the product labeled, something like "SPL: 93 dB 1 W/1 m". This measurement can also be represented as a strict [[Electrical efficiencyefficiency]] ratio of audio output ([[sound power]]) to electrical input (electrical power), but this is far less common. This method of rating speakers using SPL is often deceiving because most speakers produce very different SPLs at different frequencies of sound, often varying as much as ±10 dB throughout the speaker's usable frequency range (it generally varies less in higher quality speakers). The SPL quoted by the manufacturer is often an average over a particular range. 
+ 
:<math> 

+ 
L_\Sigma = 10\,\cdot\,{\rm log}_{10} \left(\frac{p^2_1 + p^2_2 + \cdots + p^2_n}{p^2_{\mathrm{ref}}}\right) 

+ 
= 10\,\cdot\,{\rm log}_{10} \left(\left({\frac{p_1}{p_{\mathrm{ref}}}}\right)^2 + \left({\frac{p_2}{p_{\mathrm{ref}}}}\right)^2 + \cdots + \left({\frac{p_n}{p_{\mathrm{ref}}}}\right)^2\right) 

+ 
</math> 

+ 


+ 
From the formula of the sound pressure level we find 

+ 
:<math> 

+ 
\left({\frac{p_i}{p_{\mathrm{ref}}}}\right)^2 = 10^{\frac{L_i}{10}},\qquad i=1,2,\cdots,n 

+ 
</math> 

+ 


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

+ 
:<math> 

+ 
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} 

+ 
</math> 

+ 


+ 
===Loudest sounds=== 

+ 
Sound pressure levels above 194 dB at sea level produce waveforms that are distorted. Sound waves are made up of rarefaction and compression cycles but when the compression half of the wave cycle is double normal atmospheric pressure and the rarefaction half of the cycle reaches perfect vacuum (no further air molecules to remove) then the only possible increase in sound level can be achieved on the compression side of the waveform. The rarefaction half of the cycle will be clipped at any level above 194 dB. Examples of such an occurrence are largescale manned [[rocket launch]]es, [[sonic boom]]s, munitions [[explosion]]s, [[thunder]], [[earthquake]]s and volcanic explosions.<ref>[http://www.makeitlouder.com/Decibel%20Level%20Chart.txt William Hamby (2004) ''Ultimate Sound Pressure Level Decibel Table'']</ref> 





== See also == 

== See also == 

*[[Decibel]], especially [[Decibel#Acousticsthe ''Acoustics'' section]] 

*[[Decibel]], especially [[Decibel#Acousticsthe ''Acoustics'' section]] 
− 
*[[Acoustics]] 


*[[Sone]] 

*[[Sone]] 
− 
*[[WeberFechner law]] 
+ 
*[[Loudness]] 

+ 
*[[WeberFechner law#The case of soundWeberFechner law (The case of Sound)]] 

+ 
*[[Stevens' power law]] 

*[[Sound power level]] 

*[[Sound power level]] 

+ 
*[[Amplitude]] 

+ 
*[[Acoustics]] 

+ 


+ 
==Notes and References== 

+ 
{{Reflist}} 




− 
== References == 


*Beranek, Leo L, "Acoustics" (1993) Acoustical Society of America. ISBN 088318494X 

*Beranek, Leo L, "Acoustics" (1993) Acoustical Society of America. ISBN 088318494X 

+ 
*Morfey, Christopher L, "Dictionary of Acoustics" (2001) Academic Press, San Diego. 





== External links == 

== External links == 
− 
*[http://www.sengpielaudio.com/calculatorsoundlevel.htm Conversion of sound pressure level to sound pressure] 
+ 
*[http://www.sengpielaudio.com/calculatorsoundlevel.htm Conversion of sound pressure to sound pressure level and vice versa] 
− 
*[http://www.norsonic.com/ProductsAndUses.php?menu=uses&finale=1530&nivaa=3 The level of sound (dB)] 
+ 
*[http://www.norsonic.com/ProductsAndUses.php?menu=uses&finale=1530&nivaa=3 The level of sound is dB] 
− 
*[http://www.makeitlouder.com/Decibel%20Level%20Chart.txt SPL of many different sounds] 
+ 
*[http://www.sengpielaudio.com/TableOfSoundPressureLevels.htm Table of Sound Levels  Corresponding Sound Pressure and Sound Intensity] 

+ 
*[http://www.makeitlouder.com/Decibel%20Level%20Chart.txt SPL of many different sounds  txt] 

+ 
*[http://www.sengpielaudio.com/calculatorakohm.htm Ohm's law as acoustic equivalent  calculations] 

*[http://www.rane.com/pars.html#SPL Definition of sound pressure level] 

*[http://www.rane.com/pars.html#SPL Definition of sound pressure level] 
− 
*[http://wwwccrma.stanford.edu/~jos/mdft/DB_SPL.html Has a table of SPL values] 
+ 
*[http://wwwccrma.stanford.edu/~jos/mdft/DB_SPL.html A table of SPL values] 

+ 
*[http://www.sengpielaudio.com/RelationshipsOfAcousticQuantities.pdf Relationships of acoustic quantities associated with a plane progressive acoustic sound wave  pdf] 

+ 
*[http://makeitlouder.com/Decibel%20Level%20Chart.txt Another Sound Pressure Level Decibel Table] 

+ 
*[http://www.usmotors.com/products/ProFacts/sound_power_and_sound_pressure.htm Sound pressure and sound power  two commonly confused characteristics of sound] 




− 
[[Category:Acoustics]] 
+ 
[[Category:Sound measurements]] 
− 
[[Category:Physical quantity]] 
+ 
[[Category:Auditory perception]] 
− 
[[Category:Sound]] 
+ 
[[Category:Psychophysics]] 




− 
[[de:Schalldruckpegel]] 
+ 
<! 
− 
[[es:Nivel de presión sonora]] 
+ 
[[de:Schalldruck]] 

+ 
[[et:Helirõhk]] 

+ 
[[es:Presión sonora]] 

+ 
[[gl:SPL]] 

+ 
[[is:SPL]] 

[[nl:Geluidsniveau]] 

[[nl:Geluidsniveau]] 

+ 
[[ja:音圧]] 

+ 
[[pl:Ciśnienie akustyczne]] 

+ 
[[pt:SPL]] 

[[sv:Ljudnivå]] 

[[sv:Ljudnivå]] 

+ 
[[uk:Рівень звукового тиску]] 

+ 
> 

{{enWPSound pressure}} 

{{enWPSound pressure}} 