Physics:Sound pressure

Sound measurements
Characteristic	Symbols
Sound pressure	p, SPL,LPA
Particle velocity	v, SVL
Particle displacement	δ
Sound intensity	I, SIL
Sound power	P, SWL, LWA
Sound energy	W
Sound energy density	w
Sound exposure	E, SEL
Acoustic impedance	Z
Audio frequency	AF
Transmission loss	TL
	v; t; e;

Short description: Local pressure deviation caused by a sound wave

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).^[1]

Mathematical definition

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 $p_{total} = p_{stat} + p,$ where

p_total is the total pressure,
p_stat is the static pressure.

Sound measurements

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 $𝐈 = p 𝐯,$ where

p is the sound pressure,
v is the particle velocity.

Acoustic impedance

Acoustic impedance, denoted Z and measured in Pa·m⁻³·s in SI units, is defined by^[2] $Z (s) = \frac{\hat{p} (s)}{\hat{Q} (s)},$ where

$\hat{Q} (s)$ 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^[2] $z (s) = \frac{\hat{p} (s)}{\hat{v} (s)},$ where

$\hat{p} (s)$ is the Laplace transform of sound pressure,
$\hat{v} (s)$ is the Laplace transform of particle velocity.

Particle displacement

The particle displacement of a progressive sine wave is given by $δ (𝐫, t) = δ_{m} \cos (𝐤 \cdot 𝐫 - ω t + φ_{δ, 0}),$ where

$δ_{m}$ is the amplitude of the particle displacement,
$φ_{δ, 0}$ 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 $v (𝐫, t) = \frac{\partial δ}{\partial t} (𝐫, t) = ω δ_{m} \cos (𝐤 \cdot 𝐫 - ω t + φ_{δ, 0} + \frac{π}{2}) = v_{m} \cos (𝐤 \cdot 𝐫 - ω t + φ_{v, 0}),$ $p (𝐫, t) = - ρ c^{2} \frac{\partial δ}{\partial x} (𝐫, t) = ρ c^{2} k_{x} δ_{m} \cos (𝐤 \cdot 𝐫 - ω t + φ_{δ, 0} + \frac{π}{2}) = p_{m} \cos (𝐤 \cdot 𝐫 - ω t + φ_{p, 0}),$ where

v_m is the amplitude of the particle velocity,
$φ_{v, 0}$ is the phase shift of the particle velocity,
p_m is the amplitude of the acoustic pressure,
$φ_{p, 0}$ is the phase shift of the acoustic pressure.

Taking the Laplace transforms of v and p with respect to time yields $\hat{v} (𝐫, s) = v_{m} \frac{s \cos φ_{v, 0} - ω \sin φ_{v, 0}}{s^{2} + ω^{2}},$ $\hat{p} (𝐫, s) = p_{m} \frac{s \cos φ_{p, 0} - ω \sin φ_{p, 0}}{s^{2} + ω^{2}} .$

Since $φ_{v, 0} = φ_{p, 0}$ , the amplitude of the specific acoustic impedance is given by $z_{m} (𝐫, s) = | z (𝐫, s) | = | \frac{\hat{p} (𝐫, s)}{\hat{v} (𝐫, s)} | = \frac{p_{m}}{v_{m}} = \frac{ρ c^{2} k_{x}}{ω} .$

Consequently, the amplitude of the particle displacement is related to that of the acoustic velocity and the sound pressure by $δ_{m} = \frac{v_{m}}{ω},$ $δ_{m} = \frac{p_{m}}{ω z_{m} (𝐫, s)} .$

Inverse-proportional 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/r², like the sound intensity):^[3] $p (r) \propto \frac{1}{r} .$

This relationship is an inverse-proportional law.

If the sound pressure p₁ is measured at a distance r₁ from the centre of the sphere, the sound pressure p₂ at another position r₂ can be calculated: $p_{2} = \frac{r_{1}}{r_{2}} p_{1} .$

The inverse-proportional law for sound pressure comes from the inverse-square law for sound intensity: $I (r) \propto \frac{1}{r^{2}} .$ Indeed, $I (r) = p (r) v (r) = p (r) [p * z^{- 1}] (r) \propto p^{2} (r),$ where

$v$ is the particle velocity,
$*$ is the convolution operator,
z⁻¹ is the convolution inverse of the specific acoustic impedance,

hence the inverse-proportional law: $p (r) \propto \frac{1}{r} .$

Sound pressure 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,^[4] is defined by:^[5] $L_{p} = \ln (\frac{p^{2}}{p_{0}^{2}}) Np = 2 \log_{10} (\frac{p}{p_{0}}) B = 20 \log_{10} (\frac{p}{p_{0}}) dB,$ where

p is the root mean square sound pressure,^[6]
p₀ is a reference sound pressure,
1 Np is the neper,
1 B = (⁠1/2⁠ ln 10) Np is the bel,
1 dB = (⁠1/20⁠ ln 10) Np is the decibel.

The commonly used reference sound pressure in air is^[7]

p₀ = 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 L_{p/(20 μPa)} or L_p (re 20 μPa), but the suffix notations dB SPL, dB(SPL), dBSPL, and dB_SPL are very common, even if they are not accepted by the SI.^[8]

Most sound-level measurements will be made relative to this reference, meaning 1 Pa will equal an SPL of $20 \log_{10} (\frac{1}{2 \times 1 0^{- 5}}) dB \approx 94 dB$ . In other media, such as underwater, a reference level of 1 μPa is used.^[9] These references are defined in ANSI S1.1-2013.^[10]

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 0 dB, but the upper limit is not as clearly defined. While 1 atm (194 dB peak or 191 dB SPL)^[11]^[12] 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.^[13]

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 dB_A or L_A, B-weighted sound pressure level is written either as dB_B or L_B, and C-weighted sound pressure level is written either as dB_C or L_C. Unweighted sound pressure level is called "linear sound pressure level" and is often written as dB_L or just L. Some sound measuring instruments use the letter "Z" as an indication of linear SPL.^[13]

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.^[13]

According to the inverse proportional law, when sound level L_p₁ is measured at a distance r₁, the sound level L_p₂ at the distance r₂ is $L_{p_{2}} = L_{p_{1}} + 20 \log_{10} (\frac{r_{1}}{r_{2}}) dB .$

Multiple sources

The formula for the sum of the sound pressure levels of n incoherent radiating sources is $L_{Σ} = 10 \log_{10} (\frac{p_{1}^{2} + p_{2}^{2} + \dots + p_{n}^{2}}{p_{0}^{2}}) dB = 10 \log_{10} [{(\frac{p_{1}}{p_{0}})}^{2} + {(\frac{p_{2}}{p_{0}})}^{2} + \dots + {(\frac{p_{n}}{p_{0}})}^{2}] dB .$

Inserting the formulas ${(\frac{p_{i}}{p_{0}})}^{2} = 1 0^{\frac{L_{i}}{10 dB}}, i = 1, 2, \dots, n$ in the formula for the sum of the sound pressure levels yields $L_{Σ} = 10 \log_{10} (1 0^{\frac{L_{1}}{10 dB}} + 1 0^{\frac{L_{2}}{10 dB}} + \dots + 1 0^{\frac{L_{n}}{10 dB}}) dB .$

Examples of sound pressure

Examples of sound pressure in air at standard atmospheric pressure
Source of sound	Distance	Sound pressure level^{[lower-alpha 1]}
Source of sound	Distance	(Pa)	(dB_SPL)
Shock wave (distorted sound waves > 1 atm; waveform valleys are clipped at zero pressure)^[11]^[12]		>1×10⁵	>191
Simple open-ended thermoacoustic device^[14]	^{[clarification needed]}	1.3×10⁴	176
165 km	8×10³	172
.30-06 rifle being fired^{[citation needed]}	1 m to shooter's side	7×10³	171
Firecracker^[15]	0.5 m	7×10³	171
Stun grenade^[16]	Ambient	(1.6–8)×10³	158–172
9-inch (23 cm) party balloon inflated to rupture^[17]	At ear	4.9×10³	168
9-inch (23 cm) diameter balloon crushed to rupture^[17]	At ear	1.8×10³	159
9-inch (23 cm) party balloon inflated to rupture^[17]	0.5 m	1.4×10³	157
9-inch (23 cm) diameter balloon popped with a pin^[17]	At ear	1.1×10³	155
LRAD 1000Xi Long Range Acoustic Device^[18]	1 m	8.9×10²	153
9-inch (23 cm) party balloon inflated to rupture^[17]	1 m	730	151
Jet engine^[13]	1 m	630	150
9-inch (23 cm) diameter balloon crushed to rupture^[17]	0.95 m	450	147
9-inch (23 cm) diameter balloon popped with a pin^[17]	1 m	280	143
Maximum instantaneous peak (C-weighted) for amplified sound at "safe listening" venues/events per WHO's global standard^[19]	Ambient	200	140
Instantaneous peak workplace noise (C-weighted) which legally obligates use of hearing protection by workers in the EU^[20]	At ear	140	137
Instantaneous peak workplace noise (C-weighted) which legally obligates employers to offer hearing protectors to workers in the EU^[20]	At ear	112	135
Loudest human voice^[21]	1 inch	110	135
Trumpet^[22]	0.5 m	63.2	130
1 m	20.0	120
Threshold of pain^[23]^[24]^[21]	At ear	20–100	120–134
Risk of instantaneous noise-induced hearing loss^{[citation needed]}	At ear	20.0	120
Maximum instantaneous peak (C-weighted) for amplified sound at children's venues/events complying with WHO's global safe listening standard^[25]	Ambient	20.0	120
Jet engine^{[citation needed]}	100–30 m	6–200	110–140
Two-stroke chainsaw^[26]	1 m	6	110
Jackhammer^{[citation needed]}	1 m	2.00	100
Sound level limit (A-weighted, moving average over 15-minute interval) at safe listening venues/events per WHO global standard^[27]	Ambient	2.00	100
NIOSH recommended exposure limit (REL) for workplace noise (15-minute average, A-weighted)^[28]	At ear	2.00	100
NIOSH REL for workplace noise (30-minute average, A-weighted)^[28]	At ear	1.42	97
Sound level limit (A-weighted, moving average over 15-minute interval) at children's venues/events per WHO's "safe listening" global standard^[29]	Ambient	1.0	94
NIOSH REL for workplace noise (1-hour average, A-weighted)^[28]	At ear	1.0	94
NIOSH REL for workplace noise (2-hour average, A-weighted)^[28]	At ear	0.71	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^[29]	Ambient	0.63	90
NIOSH REL for workplace noise (4-hour average, A-weighted)^[28]	At ear	0.50	88
NIOSH recommended exposure limit (REL) for workplace noise (average over 8-hour workday, A-weighted)^[28]	At ear	0.36	85
Hearing damage (over long-term exposure, need not be continuous)^[30]	At ear	0.36	85
Workplace noise level (8-hour daily average, A-weighted) that legally obligates use of hearing protection by workers in the EU^[20]	At ear	0.36	85
Vacuum cleaner, A-weighted (1981)^[31]^[32]	1.8 m	0.36	85
Workplace noise level (8-hour daily average, A-weighted) that legally obligates employers to offer hearing protectors to workers in the EU^[20]	At ear	0.2	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^[33]	At ear	0.2	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^[33]	At ear	0.11	75
Television (A-weighted)^[34]^[32]	Ambient	0.11	75
EPA-identified maximum to protect against hearing loss and other disruptive effects from noise, such as sleep disturbance, stress, learning detriment, etc.^[35]	Ambient	0.06	70
Passenger car at 30 km/h (electric and combustion engines)^[36]	10 m	0.04–0.06	65–70
Normal conversation^{[citation needed]}	1 m	2×10⁻³–0.02	40–60
Passenger car at 10 km/h (combustion)^[36]	10 m	13×10⁻³	56
Passenger car at 10 km/h (electric)^[36]	10 m	6×10⁻³	50
Very calm room^{[citation needed]}	Ambient	(2–6)×10⁻⁴	20–30
Light leaf rustling, calm breathing^[13]	Ambient	6×10⁻⁵	10
Auditory threshold at 1 kHz^[30]	At ear	2.00×10⁻⁵	0
Anechoic chamber, Orfield Labs, A-weighted^[37]^[38]	Ambient	6.8×10⁻⁶	−9.4
Anechoic chamber, University of Salford, A-weighted^[39]	Ambient	4.8×10⁻⁶	−12.4
Anechoic chamber, Microsoft, A-weighted^[40]^[41]	Ambient	1.90×10⁻⁶	−20.35

↑ All values listed are the effective sound pressure unless otherwise stated.

References

↑ "Sound Pressure Is the Force of Sound on a Surface Area Perpendicular to the Direction of the Sound". http://www.engineeringtoolbox.com/sound-pressure-d_711.html.
↑ ^2.0 ^2.1 Wolfe, J.. "What is acoustic impedance and why is it important?". University of New South Wales, Dept. of Physics, Music Acoustics. http://www.phys.unsw.edu.au/jw/z.html.
↑ Longhurst, R. S. (1967). Geometrical and Physical Optics. Norwich: Longmans. https://archive.org/details/geometricalphysi0000long.
↑ "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.
↑ A Pocket-Sized Introduction to Acoustics. Kingston upon Hull: The University of Hull. 2008. doi:10.5281/zenodo.7504060. ISBN 978-90-812588-2-1. https://hal.archives-ouvertes.fr/hal-03188302/document.
↑ Bies, David A.; Hansen, Colin (2003). Engineering Noise Control.
↑ Ross Roeser, Michael Valente, Audiology: Diagnosis (Thieme 2007), p. 240.
↑ 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 PDF.
↑ Morfey, Christopher L. (2001). Dictionary of Acoustics. San Diego: Academic Press. ISBN 978-0125069403.
↑ "Noise Terms Glossary". http://www.memtechacoustical.com/noise-terms-glossary.
↑ ^11.0 ^11.1 Self, Douglas (2020-04-17). Small Signal Audio Design. CRC Press. ISBN 978-1-000-05044-8. https://books.google.com/books?id=L2PdDwAAQBAJ&dq=194+dB+SPL&pg=PP36. "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."
↑ ^12.0 ^12.1 Guignard, J. C.; King, P.F.; North Atlantic Treaty Organization Advisory Group for Aerospace Research and Development Aerospace Medical Panel (1972). Aeromedical Aspects of Vibration and Noise. North Atlantic Treaty Organization, Advisory Group for Aerospace Research and Development. https://books.google.com/books?id=LvRJAQAAIAAJ&q=191+dB+SPL. "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"
↑ ^13.0 ^13.1 ^13.2 ^13.3 ^13.4 Winer, Ethan (2013). "1". The Audio Expert. New York and London: Focal Press. ISBN 978-0-240-82100-9.
↑ HATAZAWA, Masayasu; SUGITA, Hiroshi; OGAWA, Takahiro; SEO, Yoshitoki (2004-01-01). "Performance of a Thermoacoustic Sound Wave Generator driven with Waste Heat of Automobile Gasoline Engine". Transactions of the Japan Society of Mechanical Engineers B 70 (689): 292–299. doi:10.1299/kikaib.70.292. ISSN 0387-5016. http://ci.nii.ac.jp/naid/130004080803/.
↑ Flamme, Gregory A.; Liebe, Kevin; Wong, Adam (2009). "Estimates of the auditory risk from outdoor impulse noise I: Firecrackers". Noise and Health 11 (45): 223–230. doi:10.4103/1463-1741.56216. ISSN 1463-1741. PMID 19805932.
↑ Brueck, Scott E.; Kardous, Chuck A.; Oza, Aalok; Murphy, William J. (2014). "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". U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. https://www.cdc.gov/niosh/hhe/reports/pdfs/2013-0124-3208.pdf.
↑ ^17.0 ^17.1 ^17.2 ^17.3 ^17.4 ^17.5 ^17.6 "Did You Know How Loud Balloons Can Be?". Canadian Audiologist 3 (6). 9 January 2014. http://www.canadianaudiologist.ca/issue/volume-3-issue-6-2016/column/science-matters/. Retrieved 8 June 2018.
↑ "LRAD Corporation Product Overview for LRAD 1000Xi". http://www.lradx.com/site/content/view/2016/110/.
↑ WHO Global standard for safe listening venues and events. Geneva: World Health Organization. 2 March 2022. pp. 11,18. ISBN 978-92-4-004311-4. https://www.who.int/publications/i/item/9789240043114. Retrieved 2026-04-28.
↑ ^20.0 ^20.1 ^20.2 ^20.3 "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)". Publications Office of the European Union. 26 July 2019. https://eur-lex.europa.eu/eli/dir/2003/10.
↑ ^21.0 ^21.1 Realistic Maximum Sound Pressure Levels for Dynamic Microphones – Shure.
↑ Recording Brass & Reeds.
↑ Nave, Carl R. (2006). "Threshold of Pain". HyperPhysics. SciLinks. http://hyperphysics.phy-astr.gsu.edu/Hbase/sound/intens.html.
↑ Franks, John R.; Stephenson, Mark R.; Merry, Carol J., eds (June 1996). Preventing Occupational Hearing Loss – A Practical Guide. National Institute for Occupational Safety and Health. pp. 88. https://www.cdc.gov/niosh/docs/96-110/pdfs/96-110.pdf. Retrieved 2009-07-15.
↑ WHO Global standard for safe listening venues and events. Geneva: World Health Organization. 2 March 2022. pp. 11,18,20. ISBN 978-92-4-004311-4. https://www.who.int/publications/i/item/9789240043114. Retrieved 2026-04-28.
↑ "Decibel Table – SPL – Loudness Comparison Chart". sengpielaudio. http://www.sengpielaudio.com/TableOfSoundPressureLevels.htm.
↑ WHO Global standard for safe listening venues and events. Geneva: World Health Organization. 2 March 2022. pp. vii,8-9,13,16-17,82-83. ISBN 978-92-4-004311-4. https://www.who.int/publications/i/item/9789240043114. Retrieved 2026-04-28.
↑ ^28.0 ^28.1 ^28.2 ^28.3 ^28.4 ^28.5 "Noise-Induced Hearing Loss". Centers for Disease Control and Prevention. 30 January 2024. https://www.cdc.gov/niosh/noise/about/noise.html.
↑ ^29.0 ^29.1 WHO Global standard for safe listening venues and events. Geneva: World Health Organization. 2 March 2022. pp. 8-9,13,16-17,20,82-83. ISBN 978-92-4-004311-4. https://www.who.int/publications/i/item/9789240043114. Retrieved 2026-04-28.
↑ ^30.0 ^30.1 Hamby, William. "Ultimate Sound Pressure Level Decibel Table". http://www.makeitlouder.com/Decibel%20Level%20Chart.txt.
↑ Simpson, M.; Bruce, R. (1981). Noise in America: Extent of the noise problem (Report). Washington, DC: United States Environmental Protection Agency. EPA Rept. No. 550/9-81-101.
↑ ^32.0 ^32.1 Berger, Elliott H.; Neitzel, Rick; Kladden, Cynthia A. (22 August 2016). "Sheet 'NonOccup'". Noise Navigator Sound Level Database, Version 1.8 (Technical report). 3M, Personal Safety Division, E•A•RCAL Laboratory. Archived from the original on 2023-04-15.
↑ ^33.0 ^33.1 Safe Listening Devices and Systems: A WHO-ITU Standard. World Health Organization and International Telecommunication Union. 18 September 2019. ISBN 9789241515276. https://www.who.int/publications/i/item/9789241515276. Retrieved 2026-04-19.
↑ Neitzel, R.; Seixas, N.; Olson, J.; Daniell, W.; Goldman, B. (2004). "Nonoccupational noise: exposures associated with routine activities". The Journal of the Acoustical Society of America 115 (10): 237–245. doi:10.1121/1.1615569.
↑ "EPA Identifies Noise Levels Affecting Health and Welfare" (Press release). Environmental Protection Agency. April 2, 1974. Retrieved March 27, 2017.
↑ ^36.0 ^36.1 ^36.2 Misdariis, Nicolas; Pardo, Louis-Ferdinand (August 2017). "The sound of silence of electric vehicles – Issues and answers". Inter.noise (International Congress & Exposition on Noise Control Engineering) (Hong-Kong, China). https://hal.science/hal-01708883. "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.".
↑ "'The Quietest Place on Earth' – Guinness World Records Certificate, 2005". Orfield Labs. http://www.orfieldlabs.com/pdfs/chamber.pdf.
↑ Middlemiss, Neil (December 18, 2007). "The Quietest Place on Earth – Orfield Labs". http://www.audiojunkies.com/blog/902/the-quietest-place-on-earth-orfield-labs.
↑ Eustace, Dave. "Anechoic Chamber". University of Salford. http://www.acoustics.salford.ac.uk/facilities/?content=anechoic.
↑ "Microsoft Lab Sets New Record for the World's Quietest Place". 2015-10-02. http://www.guinnessworldrecords.com/news/2015/10/microsoft-lab-sets-new-record-for-the-worlds-quietest-place-399444. "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)."
↑ "Check Out the World's Quietest Room". http://news.microsoft.com/stories/building87/audio-lab.php.

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

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Original source: https://en.wikipedia.org/wiki/Sound pressure. Read more

[14] All values listed are the effective sound pressure unless otherwise stated.

[1] "Sound Pressure Is the Force of Sound on a Surface Area Perpendicular to the Direction of the Sound". http://www.engineeringtoolbox.com/sound-pressure-d_711.html.

[Wolfe-2] 2.0 ^2.1 Wolfe, J.. "What is acoustic impedance and why is it important?". University of New South Wales, Dept. of Physics, Music Acoustics. http://www.phys.unsw.edu.au/jw/z.html.

[3] Longhurst, R. S. (1967). Geometrical and Physical Optics. Norwich: Longmans. https://archive.org/details/geometricalphysi0000long.

[IEC60027-3-4] "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.

[5] A Pocket-Sized Introduction to Acoustics. Kingston upon Hull: The University of Hull. 2008. doi:10.5281/zenodo.7504060. ISBN 978-90-812588-2-1. https://hal.archives-ouvertes.fr/hal-03188302/document.

[6] Bies, David A.; Hansen, Colin (2003). Engineering Noise Control.

[7] Ross Roeser, Michael Valente, Audiology: Diagnosis (Thieme 2007), p. 240.

[NIST2008-8] 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 PDF.

[Morfey-9] Morfey, Christopher L. (2001). Dictionary of Acoustics. San Diego: Academic Press. ISBN 978-0125069403.

[10] "Noise Terms Glossary". http://www.memtechacoustical.com/noise-terms-glossary.

[:0-11] 11.0 ^11.1 Self, Douglas (2020-04-17). Small Signal Audio Design. CRC Press. ISBN 978-1-000-05044-8. https://books.google.com/books?id=L2PdDwAAQBAJ&dq=194+dB+SPL&pg=PP36. "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."

[:1-12] 12.0 ^12.1 Guignard, J. C.; King, P.F.; North Atlantic Treaty Organization Advisory Group for Aerospace Research and Development Aerospace Medical Panel (1972). Aeromedical Aspects of Vibration and Noise. North Atlantic Treaty Organization, Advisory Group for Aerospace Research and Development. https://books.google.com/books?id=LvRJAQAAIAAJ&q=191+dB+SPL. "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"

[Audio1-13] 13.0 ^13.1 ^13.2 ^13.3 ^13.4 Winer, Ethan (2013). "1". The Audio Expert. New York and London: Focal Press. ISBN 978-0-240-82100-9.

[15] HATAZAWA, Masayasu; SUGITA, Hiroshi; OGAWA, Takahiro; SEO, Yoshitoki (2004-01-01). "Performance of a Thermoacoustic Sound Wave Generator driven with Waste Heat of Automobile Gasoline Engine". Transactions of the Japan Society of Mechanical Engineers B 70 (689): 292–299. doi:10.1299/kikaib.70.292. ISSN 0387-5016. http://ci.nii.ac.jp/naid/130004080803/.

[16] Flamme, Gregory A.; Liebe, Kevin; Wong, Adam (2009). "Estimates of the auditory risk from outdoor impulse noise I: Firecrackers". Noise and Health 11 (45): 223–230. doi:10.4103/1463-1741.56216. ISSN 1463-1741. PMID 19805932.

[17] Brueck, Scott E.; Kardous, Chuck A.; Oza, Aalok; Murphy, William J. (2014). "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". U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. https://www.cdc.gov/niosh/hhe/reports/pdfs/2013-0124-3208.pdf.

[balloonpoploudness-18] 17.0 ^17.1 ^17.2 ^17.3 ^17.4 ^17.5 ^17.6 "Did You Know How Loud Balloons Can Be?". Canadian Audiologist 3 (6). 9 January 2014. http://www.canadianaudiologist.ca/issue/volume-3-issue-6-2016/column/science-matters/. Retrieved 8 June 2018.

[lradproductsoverview-19] "LRAD Corporation Product Overview for LRAD 1000Xi". http://www.lradx.com/site/content/view/2016/110/.

[20] WHO Global standard for safe listening venues and events. Geneva: World Health Organization. 2 March 2022. pp. 11,18. ISBN 978-92-4-004311-4. https://www.who.int/publications/i/item/9789240043114. Retrieved 2026-04-28.

[dir-2003/10/EC-21] 20.0 ^20.1 ^20.2 ^20.3 "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)". Publications Office of the European Union. 26 July 2019. https://eur-lex.europa.eu/eli/dir/2003/10.

[Shure-22] 21.0 ^21.1 Realistic Maximum Sound Pressure Levels for Dynamic Microphones – Shure.

[23] Recording Brass & Reeds.

[painthres-24] Nave, Carl R. (2006). "Threshold of Pain". HyperPhysics. SciLinks. http://hyperphysics.phy-astr.gsu.edu/Hbase/sound/intens.html.

[dictionary-25] Franks, John R.; Stephenson, Mark R.; Merry, Carol J., eds (June 1996). Preventing Occupational Hearing Loss – A Practical Guide. National Institute for Occupational Safety and Health. pp. 88. https://www.cdc.gov/niosh/docs/96-110/pdfs/96-110.pdf. Retrieved 2009-07-15.

[26] WHO Global standard for safe listening venues and events. Geneva: World Health Organization. 2 March 2022. pp. 11,18,20. ISBN 978-92-4-004311-4. https://www.who.int/publications/i/item/9789240043114. Retrieved 2026-04-28.

[sengpielaudio-27] "Decibel Table – SPL – Loudness Comparison Chart". sengpielaudio. http://www.sengpielaudio.com/TableOfSoundPressureLevels.htm.

[28] WHO Global standard for safe listening venues and events. Geneva: World Health Organization. 2 March 2022. pp. vii,8-9,13,16-17,82-83. ISBN 978-92-4-004311-4. https://www.who.int/publications/i/item/9789240043114. Retrieved 2026-04-28.

[cdc-niosh-29] 28.0 ^28.1 ^28.2 ^28.3 ^28.4 ^28.5 "Noise-Induced Hearing Loss". Centers for Disease Control and Prevention. 30 January 2024. https://www.cdc.gov/niosh/noise/about/noise.html.

[who-venue-children-30] 29.0 ^29.1 WHO Global standard for safe listening venues and events. Geneva: World Health Organization. 2 March 2022. pp. 8-9,13,16-17,20,82-83. ISBN 978-92-4-004311-4. https://www.who.int/publications/i/item/9789240043114. Retrieved 2026-04-28.

[Hamby-31] 30.0 ^30.1 Hamby, William. "Ultimate Sound Pressure Level Decibel Table". http://www.makeitlouder.com/Decibel%20Level%20Chart.txt.

[noise-in-amer-32] Simpson, M.; Bruce, R. (1981). Noise in America: Extent of the noise problem (Report). Washington, DC: United States Environmental Protection Agency. EPA Rept. No. 550/9-81-101.

[noisenav-nonoccup-33] 32.0 ^32.1 Berger, Elliott H.; Neitzel, Rick; Kladden, Cynthia A. (22 August 2016). "Sheet 'NonOccup'". Noise Navigator Sound Level Database, Version 1.8 (Technical report). 3M, Personal Safety Division, E•A•RCAL Laboratory. Archived from the original on 2023-04-15.

[who-safe-listen-34] 33.0 ^33.1 Safe Listening Devices and Systems: A WHO-ITU Standard. World Health Organization and International Telecommunication Union. 18 September 2019. ISBN 9789241515276. https://www.who.int/publications/i/item/9789241515276. Retrieved 2026-04-19.

[35] Neitzel, R.; Seixas, N.; Olson, J.; Daniell, W.; Goldman, B. (2004). "Nonoccupational noise: exposures associated with routine activities". The Journal of the Acoustical Society of America 115 (10): 237–245. doi:10.1121/1.1615569.

[36] "EPA Identifies Noise Levels Affecting Health and Welfare" (Press release). Environmental Protection Agency. April 2, 1974. Retrieved March 27, 2017.

[:2-37] 36.0 ^36.1 ^36.2 Misdariis, Nicolas; Pardo, Louis-Ferdinand (August 2017). "The sound of silence of electric vehicles – Issues and answers". Inter.noise (International Congress & Exposition on Noise Control Engineering) (Hong-Kong, China). https://hal.science/hal-01708883. "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.".

[38] "'The Quietest Place on Earth' – Guinness World Records Certificate, 2005". Orfield Labs. http://www.orfieldlabs.com/pdfs/chamber.pdf.

[39] Middlemiss, Neil (December 18, 2007). "The Quietest Place on Earth – Orfield Labs". http://www.audiojunkies.com/blog/902/the-quietest-place-on-earth-orfield-labs.

[40] Eustace, Dave. "Anechoic Chamber". University of Salford. http://www.acoustics.salford.ac.uk/facilities/?content=anechoic.

[41] "Microsoft Lab Sets New Record for the World's Quietest Place". 2015-10-02. http://www.guinnessworldrecords.com/news/2015/10/microsoft-lab-sets-new-record-for-the-worlds-quietest-place-399444. "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)."

[42] "Check Out the World's Quietest Room". http://news.microsoft.com/stories/building87/audio-lab.php.

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v t e Orders of magnitude
Quantity	Acceleration Angular momentum Angular velocity Area Bit rate Capacitance Charge Computing Currency Current Data Density Energy / Energy density / Energy flow density Entropy Force Frequency Inductance Illuminance Length Luminance / Luminous flux Magnetic field Mass Molarity Momentum Numbers Power Pressure Probability Radiation Resistance Sound pressure Specific energy Specific heat capacity Speed Temperature Time Viscosity Voltage Volume
See also	Back-of-the-envelope calculation Fermi problem Powers of 10 and decades 10th 100th 1000000th Billionth Trillionth Metric (SI) prefix Macroscopic scale Microscopic scale Quantum realm
Related	Astronomical system of units Earth's location in the Universe "Cosmic View" (1957 essay) To the Moon and Beyond (1964 film) Cosmic Zoom (1968 film) Powers of Ten (1968 and 1977 films) Cosmic Voyage (1996 documentary) Cosmic Eye (2012)
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