Sound pressure

{{Short description|Local pressure deviation caused by a sound wave}} {{Distinguish|Sound energy density}} {{Sound measurements}}

'''Sound pressure''' or '''acoustic pressure''' is the local pressure deviation from the ambient (average or equilibrium) atmospheric pressure, caused by a sound wave. In air, sound pressure can be measured using a microphone, and in water with a hydrophone. The SI unit of sound pressure is the pascal (Pa).<ref>{{cite web |title=Sound Pressure Is the Force of Sound on a Surface Area Perpendicular to the Direction of the Sound |url=http://www.engineeringtoolbox.com/sound-pressure-d_711.html |access-date=22 April 2015 }}</ref>

==Mathematical definition== thumb|upright=1.1|Sound pressure diagram: {{Ordered list|Silence|Audible sound|Atmospheric pressure|Sound pressure}}

A sound wave in a transmission medium causes a deviation (sound pressure, a ''dynamic'' pressure) in the local ambient pressure, a ''static'' pressure.

Sound pressure, denoted ''p'', is defined by <math display="block">p_\text{total} = p_\text{stat} + p,</math> where * ''p''total is the total pressure, * ''p''stat is the static pressure.

==Sound measurements==

===Sound intensity=== {{main|Sound intensity}}

In a sound wave, the complementary variable to sound pressure is the particle velocity. Together, they determine the sound intensity of the wave.

''Sound intensity'', denoted '''I''' and measured in W·m−2 in SI units, is defined by <math display="block">\mathbf I = p \mathbf v,</math> where * ''p'' is the sound pressure, * '''v''' is the particle velocity.

===Acoustic impedance=== {{main|Acoustic impedance}}

''Acoustic impedance'', denoted ''Z'' and measured in Pa·m−3·s in SI units, is defined by<ref name="Wolfe">{{cite web |last=Wolfe |first=J. |title=What is acoustic impedance and why is it important? |url=http://www.phys.unsw.edu.au/jw/z.html |publisher=University of New South Wales, Dept. of Physics, Music Acoustics |access-date=1 January 2014}}</ref> <math display="block">Z(s) = \frac{\hat{p}(s)}{\hat{Q}(s)},</math> where * <math>\hat{p}(s)</math> is the Laplace transform of sound pressure,{{citation needed|date=April 2015}} * <math>\hat{Q}(s)</math> is the Laplace transform of sound volume flow rate.

''Specific acoustic impedance'', denoted ''z'' and measured in Pa·m−1·s in SI units, is defined by<ref name="Wolfe" /> <math display="block">z(s) = \frac{\hat{p}(s)}{\hat{v}(s)},</math> where * <math>\hat{p}(s)</math> is the Laplace transform of sound pressure, * <math>\hat{v}(s)</math> is the Laplace transform of particle velocity.

===Particle displacement=== {{main|Particle displacement}}

The ''particle displacement'' of a ''progressive sine wave'' is given by <math display="block">\delta(\mathbf{r}, t) = \delta_\text{m} \cos(\mathbf{k} \cdot \mathbf{r} - \omega t + \varphi_{\delta, 0}),</math> where * <math>\delta_\text{m}</math> is the amplitude of the particle displacement, * <math>\varphi_{\delta, 0}</math> is the phase shift of the particle displacement, * '''k''' is the angular wavevector, * ''ω'' is the angular frequency.

It follows that the particle velocity and the sound pressure along the direction of propagation of the sound wave ''x'' are given by <math display="block">v(\mathbf{r}, t) = \frac{\partial \delta}{\partial t} (\mathbf{r}, t) = \omega \delta_\text{m} \cos\left(\mathbf{k} \cdot \mathbf{r} - \omega t + \varphi_{\delta, 0} + \frac{\pi}{2}\right) = v_\text{m} \cos(\mathbf{k} \cdot \mathbf{r} - \omega t + \varphi_{v, 0}),</math> <math display="block">p(\mathbf{r}, t) = -\rho c^2 \frac{\partial \delta}{\partial x} (\mathbf{r}, t) = \rho c^2 k_x \delta_\text{m} \cos\left(\mathbf{k} \cdot \mathbf{r} - \omega t + \varphi_{\delta, 0} + \frac{\pi}{2}\right) = p_\text{m} \cos(\mathbf{k} \cdot \mathbf{r} - \omega t + \varphi_{p, 0}),</math> where * ''v''m is the amplitude of the particle velocity, * <math>\varphi_{v, 0}</math> is the phase shift of the particle velocity, * ''p''m is the amplitude of the acoustic pressure, * <math>\varphi_{p, 0}</math> is the phase shift of the acoustic pressure.

Taking the Laplace transforms of ''v'' and ''p'' with respect to time yields <math display="block">\hat{v}(\mathbf{r}, s) = v_\text{m} \frac{s \cos \varphi_{v,0} - \omega \sin \varphi_{v,0}}{s^2 + \omega^2},</math> <math display="block">\hat{p}(\mathbf{r}, s) = p_\text{m} \frac{s \cos \varphi_{p,0} - \omega \sin \varphi_{p,0}}{s^2 + \omega^2}.</math>

Since <math>\varphi_{v,0} = \varphi_{p,0}</math>, the amplitude of the specific acoustic impedance is given by <math display="block">z_\text{m}(\mathbf{r}, s) = |z(\mathbf{r}, s)| = \left|\frac{\hat{p}(\mathbf{r}, s)}{\hat{v}(\mathbf{r}, s)}\right| = \frac{p_\text{m}}{v_\text{m}} = \frac{\rho c^2 k_x}{\omega}.</math>

Consequently, the amplitude of the particle displacement is related to that of the acoustic velocity and the sound pressure by <math display="block">\delta_\text{m} = \frac{v_\text{m}}{\omega},</math> <math display="block">\delta_\text{m} = \frac{p_\text{m}}{\omega z_\text{m}(\mathbf{r}, s)}.</math>

==Inverse-proportional law== {{Further|Inverse-square law}}

When measuring the sound pressure created by a sound source, it is important to measure the distance from the object as well, since the sound pressure of a ''spherical'' sound wave decreases as 1/''r'' from the centre of the sphere (and not as 1/''r''2, like the sound intensity):<ref>{{cite book |last=Longhurst |first=R. S. |title=Geometrical and Physical Optics |url=https://archive.org/details/geometricalphysi0000long |url-access=registration |year=1967 |publisher=Longmans |location=Norwich}}</ref> <math display="block">p(r) \propto \frac{1}{r}.</math>

This relationship is an ''inverse-proportional law''.

If the sound pressure ''p''1 is measured at a distance ''r''1 from the centre of the sphere, the sound pressure ''p''2 at another position ''r''2 can be calculated: <math display="block">p_2 = \frac{r_1}{r_2}\,p_1.</math>

The inverse-proportional law for sound pressure comes from the inverse-square law for sound intensity: <math display="block">I(r) \propto \frac{1}{r^2}.</math> Indeed, <math display="block">I(r) = p(r) v(r) = p(r)\left[p * z^{-1}\right](r) \propto p^2(r),</math> where * <math>v</math> is the particle velocity, * <math>*</math> is the convolution operator, * ''z''−1 is the convolution inverse of the specific acoustic impedance, hence the inverse-proportional law: <math display="block">p(r) \propto \frac{1}{r}.</math>

==Sound pressure level==  {{Other uses|Sound level (disambiguation){{!}}Sound level}}

'''Sound pressure level''' ('''SPL''') or '''acoustic pressure level''' ('''APL''') is a logarithmic measure of the effective pressure of a sound relative to a reference value.

Sound pressure level, denoted ''L''''p'' and measured in dB,<ref name="IEC60027-3">[http://webstore.iec.ch/webstore/webstore.nsf/artnum/028981 "Letter symbols to be used in electrical technology – Part 3: Logarithmic and related quantities, and their units"], ''IEC 60027-3 Ed. 3.0'', International Electrotechnical Commission, 19 July 2002.</ref> is defined by:<ref>{{cite book |vauthors=Attenborough K, Postema M |title=A Pocket-Sized Introduction to Acoustics |date=2008 |publisher=The University of Hull |location=Kingston upon Hull |url=https://hal.archives-ouvertes.fr/hal-03188302/document |isbn=978-90-812588-2-1 |doi=10.5281/zenodo.7504060 }}</ref> <math display="block">L_p = \ln\left(\frac{p^2}{p_0^2}\right) ~ \text{Np} = 2 \log_{10}\left(\frac{p}{p_0}\right)~\text{B} = 20 \log_{10}\left(\frac{p}{p_0}\right)~\text{dB},</math> where * ''p'' is the root mean square sound pressure,<ref>{{cite book |last1=Bies |first1=David A. |last2=Hansen |first2=Colin |date=2003 |title=Engineering Noise Control }}</ref> * ''p''0 is a '''reference sound pressure''', * {{nowrap|1=1 Np}} is the neper, * {{nowrap|1=1 B = ({{sfrac|2}} ln 10) Np}} is the bel, * {{nowrap|1=1 dB = ({{sfrac|20}} ln 10) Np}} is the decibel.

{{Anchor|Reference}}The commonly used reference sound pressure in air is<ref>Ross Roeser, Michael Valente, ''Audiology: Diagnosis'' (Thieme 2007), p. 240.</ref> {{Block indent | em = 1.5 | text = ''p''0 = 20 μPa,}} which is often considered as the threshold of human hearing (roughly the sound of a mosquito flying 3 m away). The proper notations for sound pressure level using this reference are {{nowrap|''L''''p''/(20 μPa)}} or {{nowrap|''L''''p'' (re 20 μPa)}}, but the suffix notations {{nowrap|dB SPL}}, {{nowrap|dB(SPL)}}, dBSPL, and dBSPL are very common, even if they are not accepted by the SI.<ref name="NIST2008">Thompson, A. and Taylor, B. N. Sec. 8.7: "Logarithmic quantities and units: level, neper, bel", ''Guide for the Use of the International System of Units (SI) 2008 Edition'', NIST Special Publication 811, 2nd printing (November 2008), SP811 [http://physics.nist.gov/cuu/pdf/sp811.pdf PDF].</ref>

Most sound-level measurements will be made relative to this reference, meaning {{nowrap|1 Pa}} will equal an SPL of <math>20 \log_{10}\left(\frac{1}{2\times10^{-5}}\right)~\text{dB}\approx 94~\text{dB}</math>. In other media, such as underwater, a reference level of {{nowrap|1 μPa}} is used.<ref name="Morfey">{{cite book |last=Morfey |first=Christopher L. |title=Dictionary of Acoustics |year=2001 |publisher=Academic Press |location=San Diego |isbn=978-0125069403}}</ref> These references are defined in ANSI S1.1-2013.<ref>{{cite web |url=http://www.memtechacoustical.com/noise-terms-glossary |title=Noise Terms Glossary |access-date=2012-10-14 }}</ref>

The main instrument for measuring sound levels in the environment is the sound level meter. Most sound level meters provide readings in A, C, and Z-weighted decibels and must meet international standards such as IEC 61672-2013.

===Examples=== The lower limit of audibility is defined as SPL of {{nowrap|0 dB}}, but the upper limit is not as clearly defined. While {{nowrap|1 atm}} ({{nowrap|194 dB peak}} or {{nowrap|191 dB SPL}})<ref name=":0">{{Cite book |last=Self |first=Douglas |url=https://books.google.com/books?id=L2PdDwAAQBAJ&dq=194+dB+SPL&pg=PP36 |title=Small Signal Audio Design |date=2020-04-17 |publisher=CRC Press |isbn=978-1-000-05044-8 |quote=this limit is reached when the rarefaction creates a vacuum, because you can't have a lower pressure than that. This corresponds to about +194 dB SPL. }}</ref><ref name=":1">{{Cite book |last1=Guignard |first1=J. C. |last2=King |first2=P.F. |author3=North Atlantic Treaty Organization Advisory Group for Aerospace Research and Development Aerospace Medical Panel |date=1972 |url=https://books.google.com/books?id=LvRJAQAAIAAJ&q=191+dB+SPL |title=Aeromedical Aspects of Vibration and Noise |publisher=North Atlantic Treaty Organization, Advisory Group for Aerospace Research and Development |quote=In air at an assumed atmospheric pressure of 1 bar (100,000 N/m2) this occurs theoretically at approximately 191 dB SPL (working with rms values }}</ref> is the largest pressure variation an undistorted sound wave can have in Earth's atmosphere (i. e., if the thermodynamic properties of the air are disregarded; in reality, the sound waves become progressively non-linear starting over 150 dB), larger sound waves can be present in other atmospheres or other media, such as underwater or through the Earth.<ref name="Audio1">{{cite book |last=Winer |first=Ethan |date=2013 |title=The Audio Expert |location=New York and London |publisher=Focal Press |chapter=1 |isbn=978-0-240-82100-9 }}</ref>

[[File:Lindos1.svg|thumb|upright=1.1|Equal-loudness contour, showing sound-pressure-vs-frequency at different perceived loudness levels]]

Ears detect changes in sound pressure. Human hearing does not have a flat spectral sensitivity (frequency response) relative to frequency versus amplitude. Humans do not perceive low- and high-frequency sounds as well as they perceive sounds between 3,000 and 4,000 Hz, as shown in the equal-loudness contour. Because the frequency response of human hearing changes with amplitude, three weightings have been established for measuring sound pressure: A, B and C.

In order to distinguish the different sound measures, a suffix is used: A-weighted sound pressure level is written either as dBA or LA, B-weighted sound pressure level is written either as dBB or LB, and C-weighted sound pressure level is written either as dBC or LC. Unweighted sound pressure level is called "linear sound pressure level" and is often written as dBL or just L. Some sound measuring instruments use the letter "Z" as an indication of linear SPL.<ref name="Audio1" />

===Distance=== The distance of the measuring microphone from a sound source is often omitted when SPL measurements are quoted, making the data useless, due to the inherent effect of the inverse proportional law. In the case of ambient environmental measurements of "background" noise, distance need not be quoted, as no single source is present, but when measuring the noise level of a specific piece of equipment, the distance should always be stated. A distance of one metre (1 m) from the source is a frequently used standard distance. Because of the effects of reflected noise within a closed room, the use of an anechoic chamber allows sound to be comparable to measurements made in a free field environment.<ref name="Audio1" />

According to the inverse proportional law, when sound level ''L''''p''1 is measured at a distance ''r''1, the sound level ''L''''p''2 at the distance ''r''2 is <math display="block">L_{p_2} = L_{p_1} + 20 \log_{10}\left( \frac{r_1}{r_2} \right)~\text{dB}.</math>

===Multiple sources=== The formula for the sum of the sound pressure levels of ''n'' incoherent radiating sources is <math display="block">L_\Sigma = 10 \log_{10}\left(\frac{p_1^2 + p_2^2 + \dots + p_n^2}{p_0^2}\right)~\text{dB} = 10 \log_{10}\left[\left(\frac{p_1}{p_0}\right)^2 + \left(\frac{p_2}{p_0}\right)^2 + \dots + \left(\frac{p_n}{p_0}\right)^2\right]~\text{dB}.</math>

Inserting the formulas <math display="block">\left(\frac{p_i}{p_0}\right)^2 = 10^{\frac{L_i}{10~\text{dB}}},\quad i = 1, 2, \ldots, n</math> in the formula for the sum of the sound pressure levels yields <math display="block">L_\Sigma = 10 \log_{10} \left(10^{\frac{L_1}{10~\text{dB}}} + 10^{\frac{L_2}{10~\text{dB}}} + \dots + 10^{\frac{L_n}{10~\text{dB}}} \right)~\text{dB}.</math>

==Examples of sound pressure==  {| class="wikitable sortable" |+ Examples of sound pressure in air at standard atmospheric pressure |- ! rowspan="2" | Source of sound ! rowspan="2" | Distance ! colspan="2" | Sound pressure level{{efn|All values listed are the effective sound pressure unless otherwise stated.}} |- ! (Pa) ! (dB{{sub|SPL}}) |- | Shock wave (distorted sound waves > 1 atm; waveform valleys are clipped at zero pressure)<ref name=":0" /><ref name=":1" /> | | align="right" | >1{{e|5}} | align="right" | >191 |- | Simple open-ended thermoacoustic device<ref>{{Cite journal |title=Performance of a Thermoacoustic Sound Wave Generator driven with Waste Heat of Automobile Gasoline Engine |url=http://ci.nii.ac.jp/naid/130004080803/ |journal=Transactions of the Japan Society of Mechanical Engineers B |date=2004-01-01 |issn=0387-5016 |pages=292–299 |volume=70 |issue=689 |doi=10.1299/kikaib.70.292 |first1=Masayasu |last1=HATAZAWA |first2=Hiroshi |last2=SUGITA |first3=Takahiro |last3=OGAWA |first4=Yoshitoki |last4=SEO |doi-access=free}}</ref> | {{Clarify|date=January 2016}} | align="right" | 1.3{{e|4}} | align="right" | 176 |- |1883 eruption of Krakatoa<ref>{{Cite web |title=Krakatoa Eruption – The Loudest Sound |url=https://www.bksv.com/en/knowledge/blog/perspectives/krakatoa-eruption-sound|access-date=2021-03-24 |website=Brüel & Kjær |quote=160 km (99 miles) away from the source, registered a sound pressure level spike of more than 2½ inches of mercury (8.5 kPa), equivalent to 172 decibels. }}</ref><ref name="winchester">{{Cite book |last=Winchester |first=Simon |title=Krakatoa: The Day the World Exploded, August 27, 1883 |title-link=Krakatoa: The Day the World Exploded |publisher=Penguin/Viking |date=2003 |isbn=978-0-670-91430-2 |page=218 |author-link=Simon Winchester }}</ref> |165 km | align="right" | 8{{e|3}} | align="right" | 172 |- | .30-06 rifle being fired{{cn|date=April 2026}} | 1 m to shooter's side | align="right" | 7{{e|3}} | align="right" | 171 |- |Firecracker<ref>{{Cite journal |last1=Flamme |first1=Gregory A. |last2=Liebe |first2=Kevin |last3=Wong |first3=Adam |date=2009 |title=Estimates of the auditory risk from outdoor impulse noise I: Firecrackers |journal=Noise and Health |volume=11 |issue=45 |pages=223–230 |doi=10.4103/1463-1741.56216 |pmid=19805932 |issn=1463-1741 |doi-access=free }}</ref> |0.5 m |align="right" | 7{{e|3}} |align="right" | 171 |- | Stun grenade<ref>{{Cite web |url = https://www.cdc.gov/niosh/hhe/reports/pdfs/2013-0124-3208.pdf |title = NIOSH HHE Report No. 2013-0124-3208. Health hazard evaluation report: measurement of exposure to impulsive noise at indoor and outdoor firing ranges during tactical training exercises |last1=Brueck |first1=Scott E. |last2=Kardous |first2=Chuck A. |last3=Oza |first3=Aalok |last4=Murphy |first4=William J. |place=Cincinnati, OH |publisher=U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health |date = 2014 }}</ref> | Ambient | align="right" | {{nobr|(1.6–8)}}{{e|3}} | align="right" | 158–172 |- | {{convert|9|in|cm|adj=on}} party balloon inflated to rupture<ref name="balloonpoploudness">{{cite journal |title=Did You Know How Loud Balloons Can Be? |journal=Canadian Audiologist |date=9 January 2014 |volume=3 |issue=6 |url=http://www.canadianaudiologist.ca/issue/volume-3-issue-6-2016/column/science-matters/ |access-date=8 June 2018}}</ref> | At ear | align="right" | 4.9×103 | align="right" | 168 |- | {{convert|9|in|cm|adj=on}} diameter balloon crushed to rupture<ref name="balloonpoploudness" /> | At ear | align="right" | 1.8×103 | align="right" | 159 |- |{{convert|9|in|cm|adj=on}} party balloon inflated to rupture<ref name="balloonpoploudness" /> | 0.5 m |align="right" | 1.4×103 |align="right" | 157 |- | {{convert|9|in|cm|adj=on}} diameter balloon popped with a pin<ref name="balloonpoploudness" /> | At ear | align="right" | 1.1×103 | align="right" | 155 |- | LRAD 1000Xi Long Range Acoustic Device<ref name="lradproductsoverview">{{cite web |title=LRAD Corporation Product Overview for LRAD 1000Xi |url=http://www.lradx.com/site/content/view/2016/110/ |access-date=29 May 2014 |archive-date=16 March 2014 |archive-url=https://web.archive.org/web/20140316054039/http://www.lradx.com/site/content/view/2016/110/ |url-status=dead }}</ref> | 1 m | align="right" | 8.9×102 | align="right" | 153 |- | {{convert|9|in|cm|adj=on}} party balloon inflated to rupture<ref name="balloonpoploudness" /> | 1 m | align="right" | 730 | align="right" | 151 |- | Jet engine<ref name="Audio1" /> | 1 m | align="right" | 630 | align="right" | 150 |- | {{convert|9|in|cm|adj=on}} diameter balloon crushed to rupture<ref name="balloonpoploudness" /> | 0.95 m | align="right" | 450 | align="right" | 147 |- | {{convert|9|in|cm|adj=on}} diameter balloon popped with a pin<ref name="balloonpoploudness" /> | 1 m | align="right" | 280 | align="right" | 143 |- | Maximum instantaneous peak (C-weighted) for amplified sound at "safe listening" venues/events per WHO's global standard<ref>{{cite book |date=2 March 2022 |title=WHO Global standard for safe listening venues and events |isbn=978-92-4-004311-4 |url=https://www.who.int/publications/i/item/9789240043114 |publisher=World Health Organization |location=Geneva |access-date=2026-04-28 |pages=11,18}}</ref> | Ambient | align="right" | 200 | align="right" | 140 |- | Instantaneous peak workplace noise (C-weighted) which legally obligates use of hearing protection by workers in the EU<ref name="dir-2003/10/EC"/> | At ear | align="right" | 140 | align="right" | 137 |- | Instantaneous peak workplace noise (C-weighted) which legally obligates employers to offer hearing protectors to workers in the EU<ref name="dir-2003/10/EC"/> | At ear | align="right" | 112 | align="right" | 135 |- | Loudest human voice<ref name="Shure" /> | 1 inch | align="right" | 110 | align="right" | 135 |- | Trumpet<ref>[http://www.soundonsound.com/sos/jan99/articles/brass778.htm Recording Brass & Reeds].</ref> | 0.5 m | align="right" | 63.2 | align="right" | 130 |- | Vuvuzela horn<ref>{{Cite journal |last1=Swanepoel |first1=De Wet |author-link=De Wet Swanepoel |last2=Hall III |first2=James W. |last3=Koekemoer |first3=Dirk |date=February 2010 |title=Vuvuzela – good for your team, bad for your ears |url=http://www.scielo.org.za/pdf/samj/v100n2/v100n2a15.pdf |journal=South African Medical Journal |volume=100 |issue=4 |pages=99–100 |doi=10.7196/samj.3697 |doi-broken-date=12 July 2025 |pmid=20459912 |doi-access=free |hdl=2263/13136 }}</ref> | 1 m | align="right" | 20.0 | align="right" | 120 |- | Threshold of pain<ref name="painthres">{{cite web |last=Nave |first=Carl R. |title=Threshold of Pain |work=HyperPhysics |publisher=SciLinks |year=2006 |url=http://hyperphysics.phy-astr.gsu.edu/Hbase/sound/intens.html |access-date=2009-06-16 }}</ref><ref name="dictionary">{{Cite book |editor1-last=Franks |editor1-first=John R. |editor2-last=Stephenson |editor2-first=Mark R. |editor3-last=Merry |editor3-first =Carol J. |date=June 1996 |title=Preventing Occupational Hearing Loss – A Practical Guide |publisher=National Institute for Occupational Safety and Health |pages=88 |url=https://www.cdc.gov/niosh/docs/96-110/pdfs/96-110.pdf |access-date=2009-07-15}}</ref><ref name="Shure">[https://service.shure.com/s/article/can-a-dynamic-microphone-handle-really-loud-sounds-maximum-spl?language=en_US Realistic Maximum Sound Pressure Levels for Dynamic Microphones] – Shure.</ref> | At ear | align="right" | 20–100 | align="right" | 120–134 |- | Risk of instantaneous noise-induced hearing loss{{cn|date=April 2026}} | At ear | align="right" | 20.0 | align="right" | 120 |- | Maximum instantaneous peak (C-weighted) for amplified sound at children's venues/events complying with WHO's global safe listening standard<ref>{{cite book |date=2 March 2022 |title=WHO Global standard for safe listening venues and events |isbn=978-92-4-004311-4 |url=https://www.who.int/publications/i/item/9789240043114 |publisher=World Health Organization |location=Geneva |access-date=2026-04-28 |pages=11,18,20}}</ref> | Ambient | align="right" | 20.0 | align="right" | 120 |- | Jet engine{{cn|date=April 2026}} | 100–30 m | align="right" | 6–200 | align="right" | 110–140 |- | Two-stroke chainsaw<ref name="sengpielaudio">{{cite web |work=sengpielaudio |title=Decibel Table – SPL – Loudness Comparison Chart |url=http://www.sengpielaudio.com/TableOfSoundPressureLevels.htm |access-date=5 Mar 2012}}</ref> | 1 m | align="right" | 6 | align="right" | 110 |- | Jackhammer{{cn|date=April 2026}} | 1 m | align="right" | 2.00 | align="right" | 100 |- | Sound level limit (A-weighted, moving average over 15-minute interval) at safe listening venues/events per WHO global standard<ref>{{cite book |date=2 March 2022 |title=WHO Global standard for safe listening venues and events |isbn=978-92-4-004311-4 |url=https://www.who.int/publications/i/item/9789240043114 |publisher=World Health Organization |location=Geneva |access-date=2026-04-28 |pages=vii,8-9,13,16-17,82-83 }}</ref> | Ambient | align="right" | 2.00 | align="right" | 100 |- | NIOSH recommended exposure limit (REL) for workplace noise (15-minute average, A-weighted)<ref name="cdc-niosh"/> | At ear | align="right" | 2.00 | align="right" | 100 |- | NIOSH REL for workplace noise (30-minute average, A-weighted)<ref name="cdc-niosh"/> | At ear | align="right" | 1.42 | align="right" | 97 |- | Sound level limit (A-weighted, moving average over 15-minute interval) at children's venues/events per WHO's "safe listening" global standard<ref name="who-venue-children">{{cite book |date=2 March 2022 |title=WHO Global standard for safe listening venues and events |isbn=978-92-4-004311-4 |url=https://www.who.int/publications/i/item/9789240043114 |publisher=World Health Organization |location=Geneva |access-date=2026-04-28 |pages=8-9,13,16-17,20,82-83}}</ref> | Ambient | align="right" | 1.0 | align="right" | 94 |- | NIOSH REL for workplace noise (1-hour average, A-weighted)<ref name="cdc-niosh"/> | At ear | align="right" | 1.0 | align="right" | 94 |- | NIOSH REL for workplace noise (2-hour average, A-weighted)<ref name="cdc-niosh"/> | At ear | align="right" | 0.71 | align="right" | 91 |- | Sound level limit (A-weighted, moving average over 15-minute interval) at venues/events for "young children" per WHO's safe listening global standard<ref name="who-venue-children"/> | Ambient | align="right" | 0.63 | align="right" | 90 |- | NIOSH REL for workplace noise (4-hour average, A-weighted)<ref name="cdc-niosh"/> | At ear | align="right" | 0.50 | align="right" | 88 |- | NIOSH recommended exposure limit (REL) for workplace noise (average over 8-hour workday, A-weighted)<ref name="cdc-niosh">{{cite web |date=30 January 2024 |title=Noise-Induced Hearing Loss |url=https://www.cdc.gov/niosh/noise/about/noise.html |website=National Institute for Occupational Safety and Health |publisher=Centers for Disease Control and Prevention |access-date=2026-04-19 }}</ref> | At ear | align="right" | 0.36 | align="right" | 85 |- | Hearing damage (over long-term exposure, need not be continuous)<ref name="Hamby" /> | At ear | align="right" | 0.36 | align="right" | 85 |- | Workplace noise level (8-hour daily average, A-weighted) that legally obligates use of hearing protection by workers in the EU<ref name="dir-2003/10/EC">{{cite web |url=https://eur-lex.europa.eu/eli/dir/2003/10 |date=26 July 2019 |title=Consolidated text: Directive 2003/10/EC of the European Parliament and of the Council of 6 February 2003 on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (noise) |website=EUR-Lex |publisher=Publications Office of the European Union |access-date=2026-04-12 |id=Document 02003L0010-20190726 }}</ref> | At ear | align="right" | 0.36 | align="right" | 85 |- | Vacuum cleaner, A-weighted (1981)<ref name="noise-in-amer">{{cite report |last1=Simpson |first1=M. |last2=Bruce |first2=R. |date=1981 |title=Noise in America: Extent of the noise problem |location=Washington, DC |publisher=United States Environmental Protection Agency |id=EPA Rept. No. 550/9-81-101}}</ref><ref name="noisenav-nonoccup"/> | 1.8 m | align="right" | 0.36 | align="right" | 85 |- | Workplace noise level (8-hour daily average, A-weighted) that legally obligates employers to offer hearing protectors to workers in the EU<ref name="dir-2003/10/EC"/> | At ear | align="right" | 0.2 | align="right" | 80 |- | Average level (A-weighted) at 40 hours per week (on a rolling basis) equivalent to the "sound allowance" for a "safe listening device" in "Mode 1: WHO standard level for adults" per WHO/ITU-T Rec. H.870<ref name="who-safe-listen">{{cite book |date=18 September 2019 |title=Safe Listening Devices and Systems: A WHO-ITU Standard |url=https://www.who.int/publications/i/item/9789241515276 |publisher=World Health Organization and International Telecommunication Union |page= |isbn=9789241515276 |access-date=2026-04-19 }}</ref> | At ear | align="right" | 0.2 | align="right" | 80 |- | Average level (A-weighted) at 40 hours per week (on a rolling basis) equivalent to the "sound allowance" for a "safe listening device" in "Mode 2: WHO standard level for sensitive users (e.g. children)" per WHO/ITU-T Rec. H.870<ref name="who-safe-listen"/> | At ear | align="right" | 0.11 | align="right" | 75 |- | Television (A-weighted)<ref>{{cite journal |last1=Neitzel |first1=R. |last2=Seixas |first2=N. |last3=Olson |first3=J. |last4=Daniell |first4=W. |last5=Goldman |first5=B. |date=2004 |title=Nonoccupational noise: exposures associated with routine activities |journal=The Journal of the Acoustical Society of America |volume=115 |issue=10 |pages=237–245 |doi=10.1121/1.1615569 }}</ref><ref name="noisenav-nonoccup">{{cite tech report |title=Noise Navigator Sound Level Database, Version 1.8 |publisher=3M, Personal Safety Division, E•A•RCAL Laboratory |first1=Elliott H. |last1=Berger |first2=Rick |last2=Neitzel |first3=Cynthia A. |last3=Kladden |date=22 August 2016 |url=https://multimedia.3m.com/mws/media/1262312O/3m-noise-navigator.xlsx |archive-url=https://web.archive.org/web/20230415035947/https://multimedia.3m.com/mws/media/1262312O/3m-noise-navigator.xlsx | archive-date=2023-04-15 |chapter=Sheet 'NonOccup'}}</ref> | Ambient | align="right" | 0.11 | align="right" | 75 |- | EPA-identified maximum to protect against hearing loss and other disruptive effects from noise, such as sleep disturbance, stress, learning detriment, etc.<ref>{{cite press release |title=EPA Identifies Noise Levels Affecting Health and Welfare |url=https://www.epa.gov/archive/epa/aboutepa/epa-identifies-noise-levels-affecting-health-and-welfare.html |publisher=Environmental Protection Agency |date=April 2, 1974 |access-date=March 27, 2017}}</ref> | Ambient | align="right" | 0.06 | align="right" | 70 |- | Passenger car at 30 km/h (electric and combustion engines)<ref name=":2">{{Cite journal |last1=Misdariis |first1=Nicolas |last2=Pardo |first2=Louis-Ferdinand |date=August 2017 |title=The sound of silence of electric vehicles – Issues and answers |url=https://hal.science/hal-01708883 |journal=Inter.noise (International Congress & Exposition on Noise Control Engineering) |location=Hong-Kong, China |quote=Figure 1 shows the noise level generated when three vehicles go by, according to their speed. At low speed, the difference between a vehicle with an engine and an electric vehicle can be significant (over 10 dB(A)). Above 20 to 30 km/h, the noise made by the tyres on the road surface becomes dominant and the differences become less pronounced.}}</ref> | 10 m | align="right" | 0.04–0.06 | align="right" | 65–70 |- | Normal conversation{{cn|date=April 2026}} | 1 m | align="right" | 2{{e|−3}}–0.02 | align="right" | 40–60 |- | Passenger car at 10 km/h (combustion)<ref name=":2" /> | 10 m | align="right" | 13{{e|−3}} | align="right" | 56 |- |Passenger car at 10 km/h (electric)<ref name=":2" /> |10 m | align="right" | 6{{e|−3}} | align="right" | 50 |- | Very calm room{{cn|date=April 2026}} | Ambient | align="right" | {{nobr|(2–6)}}{{e|−4}} | align="right" | 20–30 |- | Light leaf rustling, calm breathing<ref name="Audio1" /> | Ambient | align="right" | 6{{e|−5}} | align="right" | 10 |- | Auditory threshold at 1 kHz<ref name="Hamby">{{Cite web |url=http://www.makeitlouder.com/Decibel%20Level%20Chart.txt |title=Ultimate Sound Pressure Level Decibel Table |archive-url=https://web.archive.org/web/20051019001826/http://www.makeitlouder.com/Decibel%20Level%20Chart.txt |archive-date=2005-10-19 |url-status=live |first=William |last=Hamby }}</ref> | At ear | align="right" | 2.00{{e|−5}} | align="right" | 0 |- | Anechoic chamber, Orfield Labs, A-weighted<ref>{{Cite web |url=http://www.orfieldlabs.com/pdfs/chamber.pdf |title='The Quietest Place on Earth' – Guinness World Records Certificate, 2005 |publisher=Orfield Labs }}</ref><ref>{{Cite web |last=Middlemiss |first=Neil |date=December 18, 2007 |url=http://www.audiojunkies.com/blog/902/the-quietest-place-on-earth-orfield-labs |title=The Quietest Place on Earth – Orfield Labs |website=Audio Junkies |archive-url=https://web.archive.org/web/20101121101851/http://www.audiojunkies.com/blog/902/the-quietest-place-on-earth-orfield-labs |archive-date=2010-11-21 }}</ref> | Ambient | align="right" | 6.8{{e|−6}} | align="right" | −9.4 |- | Anechoic chamber, University of Salford, A-weighted<ref>{{Cite web |last=Eustace |first=Dave |url=http://www.acoustics.salford.ac.uk/facilities/?content=anechoic |title=Anechoic Chamber |publisher=University of Salford |archive-url=https://web.archive.org/web/20190304052554/http://www.acoustics.salford.ac.uk/facilities/?content=anechoic |archive-date=2019-03-04 }}</ref> | Ambient | align="right" | 4.8{{e|−6}} | align="right" | −12.4 |- | Anechoic chamber, Microsoft, A-weighted<ref>{{Cite web |url=http://www.guinnessworldrecords.com/news/2015/10/microsoft-lab-sets-new-record-for-the-worlds-quietest-place-399444 |title=Microsoft Lab Sets New Record for the World's Quietest Place |date=2015-10-02 |access-date=2016-09-20 |quote=The computer company has built an anechoic chamber in which highly sensitive tests reported an average background noise reading of an unimaginably quiet −20.35 dBA (decibels A-weighted).}}</ref><ref>{{Cite web |url=http://news.microsoft.com/stories/building87/audio-lab.php |title=Check Out the World's Quietest Room |website=Microsoft: Inside B87 |access-date=2016-09-20 }}</ref> | Ambient | align="right" | 1.90{{e|−6}} | align="right" | −20.35 |} {{Notelist}}

==See also== * {{Annotated link|Acoustics}} * {{Annotated link|Phon}} * {{Annotated link|Loudness}} * {{Annotated link|Sone}} * {{Annotated link|Sound level meter}} * {{Annotated link|Stevens's power law}} * {{Annotated link|Weber–Fechner law}}

==References== {{Reflist}}

;General *Beranek, Leo L., ''Acoustics'' (1993), Acoustical Society of America, {{ISBN|0-88318-494-X}}. *Daniel R. Raichel, ''The Science and Applications of Acoustics'' (2006), Springer New York, {{ISBN|1441920803}}.

==External links== * {{Commons category-inline}} * [http://www.usmotors.com/products/ProFacts/sound_power_and_sound_pressure.htm Sound Pressure and Sound Power, Two Commonly Confused Characteristics of Sound] * [http://www.gcaudio.com/resources/howtos/loudness.html Decibel (Loudness) Comparison Chart]

Category:Acoustic equations Category:Acoustics Category:Physical quantities Category:Sound Category:Sound measurements