Talk:Sound pressure

From Wikipedia, the free encyclopedia
Jump to: navigation, search
WikiProject Physics / Acoustics  (Rated Start-class, High-importance)
WikiProject icon This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Start-Class article Start  This article has been rated as Start-Class on the project's quality scale.
 High  This article has been rated as High-importance on the project's importance scale.
This article is supported by Acoustics Taskforce.
WikiProject Professional sound production (Rated Start-class, High-importance)
WikiProject icon This article is within the scope of WikiProject Professional sound production, a collaborative effort to improve the coverage of sound recording and reproduction on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Start-Class article Start  This article has been rated as Start-Class on the project's quality scale.
 High  This article has been rated as High-importance on the project's importance scale.

"M1 Garand" vs "Rifle"[edit]

The table "Examples of sound pressure and sound pressure levels" says this:
Rifle being fired at 1 m 200 Pa
M1 Garand being fired at 1 m 5,000 Pa

But the M1 Garand is a rifle. What kind of rifle does the other entry refer to? I found no source for the data in the table. -- (talk) 11:21, 29 September 2008 (UTC)


Just because the article is discussing SPL overall, I thought it worth mentioning briefly that in underwater acoustics, p0 is actually 1uPa higher up. It's referenced further down but since p0 in air is stated initially, no reason no to mention it for water then. User:S., 19 Oct 2006


I decided to remove the section that described pressure and listed equations, a really believe a link to the pressure article is sufficient.

The part that I decided cut:

p = sound pressure in Pa = pascal = N/m²
F = force in newton N, and A = area in m² or S = surface.

The SI unit is pascal with the symbol Pa. One pascal equals a pressure of one newton per m2

Danny Beardsley 10:18, 13 Nov 2004 (UTC)

Pressure symbol[edit]

"The symbol for pressure is the lower case p. (The upper case P is the symbol for power. This is often misprinted.)"

says who(m)? - Omegatron 04:10, Mar 30, 2005 (UTC)
The treatment of sound pressure level appears to be inconsistent with standard reference works across Wikipedia. Both Kinsler and Frey's "Fundamentals of Acoustics" (2nd edition) and Robert Urick's "Principles of Underwater Sound" (3rd edition) indicate that a measured intensity is a level (Urick p.15) or sound pressure level (K&F) relative to a reference effective pressure (K&F pp.125-126). Both of these sources recommend reporting decibels with an explicit listing of the reference effective pressure, like so: "74 dB re 20 micropascals", where the number and units following re is the reference effective pressure. I was working on the decibel article's misuse of SPL as if it specified a reference effective pressure when I realized that several other articles were similarly affected. I don't have time at the moment to correct all of them, but I will drop this comment into the discussion part of each article that I have come across so far with this problem. Level or sound pressure level in both these standard texts simply refer to a measurement in the sound field and are not indications of a specific reference pressure upon which the decibel is based. In other words, "dBSPL" is an incorrect means of attempting to refer to the in-air reference effective pressure. In no article thus far have I seen the "dBSPL" usage tied to an authoritative source. By contrast, the "dB re" formalism is common to both standard reference works that I have cited. (BTW, Urick uses a lowercase p to refer to pressure, and K&F use an uppercase P. Go figure.) Wesley R. Elsberry 10:34, 9 April 2006 (UTC)
Other sites using the "dB re" formalism: Oceans of Noise (explicit in defining SPL and SIL in terms of "dB re"), SURTASS LFA, NIST listing SPL in terms of "dB re", and Acoustic Impacts on Marine Mammals. But the best thing I've found has to be ASACOS Rules for Preparation of American National Standards in ACOUSTICS, MECHANICAL VIBRATION AND SHOCK, BIOACOUSTICS, and NOISE, which states:

3.16 Unit symbols

3.16.1 When to use unit symbols

In the text of the standard, the unit symbol for a quantity shall be used only when the unit is preceded by a numeral. When the unit is not preceded by a numeral, spell out the name of the unit. In text, even when a numerical value is given, it is desirable to spell out the name of the unit. Moreover, the name shall be spelled out when it first appears in the text, and more often if the text is lengthy.

Thus, in text write "...a sound pressure level of 73 dB; or "...a sound pressure level of 73 decibels." Do not write "sound pressure level in dB"; the correct form is "sound pressure level in decibels." Do not write "dB levels", "dB readings", or "dB SPL."

Levels or readings are not of decibels; they are of sound pressure levels or some other acoustical quantity. Write out the word "decibel" for such applications, and be sure that the word 'decibel' follows, not precedes the description of the relevant acoustical quantity.

The guidelines given for the National Standards clearly excludes the use of "dB SPL". Wesley R. Elsberry 17:04, 9 April 2006 (UTC)

Equation order[edit]

I changed the order of the equation to put the 10log() before the 20 log(). This is because it emphasises that decibels are always 10log(power ratio) and this equates to 10log(sound pressure squared ratio) which equates to 20log(sound pressure ratio). Richardng 17:33, 2 June 2006 (UTC)


Wikipedia policy discourages linking directly to a disambiguation page, unless it's the amorphousness of the term that's under discussion. "Strength" appears to be used in a somewhat-specific sense in the article, but I can't figure out what precisely is meant, nor which article I should re-link the word to. Signal strength? Would someone with expertise help, please? Sanguinity 19:47, 24 August 2006 (UTC)

Following the lead set on "Intensity", I'm redirecting "strength" to the wiktionary entry, and will do the same on the other sound-measurement pages (phon, sound intensity). Again, if a particular sense of "strength" is meant, please re-link as appropriate. Sanguinity 18:33, 25 August 2006 (UTC)

Distance Law[edit]

The entry for the distance law appears to be completely mucked up. The confusion between SPL diminishing as 1/r vs. 1/r^2 is ubiquitous. There are many sites on the web advocating each. I suspect that this is a confusion rooted in misunderstanding and misapplication of 20 log (SPL / SPL_ref) vs. 10 log (Sound_Power / Sound_Power_ref). That sound power is proportional to the square of pressure actually has nothing to do with the omnidirectional spread of a punctual sound as the surface of a sphere. But maybe someone has confused the two applications of square-law.

Is there anyone who really understands and has experience with this? If so, please clean up the Distance Law section! — Preceding unsigned comment added by Sjgooch (talkcontribs) 05:58, 13 March 2011 (UTC)

I see nothing wrong with the section entitled "Distance law". Could you be more specific? Dondervogel 2 (talk) 19:25, 13 March 2011 (UTC)
I too see nothing factually wrong with this section. It could stand much cleaning up and shortening though. --catslash (talk) 22:31, 13 March 2011 (UTC)
What I gather is that Sound pressure falls off at 1/r. That's good because this article is about Sound pressure. Sound intensity or Sound power falls off at 1/r^2 and the article takes pains to keep readers on track with this. And then the confusion. The next section is about Sound pressure level (SPL), which has a 20log or p^2 definition so must actually be a power or intensity measure, not level. As such SPL follows a 1/r^2 distance law. In general, we've got a bit of a mess going on with the multitude of sound pressure/intensity/power articles. --Kvng (talk) 15:15, 15 March 2011 (UTC)

Unuseful entries in the SPL table[edit]

Is there any reason to include the Krakatoa entry in this table? It ha blank values and even explictly states it is unmeasured. It seems to be nothing more than a waste of space. I didn't remove it immediately thinking there may be a reference that was being checked and I caught it in a 5 minute hiatus, but if that is not the case I suggest it be removed. —Preceding unsigned comment added by (talk) 15:35, 19 August 2010 (UTC)

Discrepancies in the SPL table[edit]

With regard to the table labeled “Examples of sound pressure and sound pressure levels”, I've noticed a “Rifle being fired at 1 m” being given as an example of a sound that is 200 Pa in amplitude, with an SPL of140 dB.

  Higher up, an M1 Garand is offered as an example of a sound having an amplitude of 5,000 Pa and an SPL of 168 dB.  An M1 Garand, of course, is a kind of a rifle.

  I think that the “Rifle being fired at 1 m” entry cannot possibly be taken as valid without specifying what kind of rifle it is. A “rifle” could be anything from a .177 caliber air rifle up through the M1 Garand, up to a .70 caliber big-game hunting rifle and beyond.  Obviously, it's something that isn't as loud as an M1 Garand. 14:34, 10 March 2007 (UTC)  — Bob Blaylock, N38°35′W121°29′

I am not sure how to correct this. I had similar doubts regarding the "jet engine" and the "jet" entries in the table. Right now I have added unreferenced tag to the table. If I an able to find some good references, I will update the table. -- Myth (Talk) 03:59, 11 March 2007 (UTC)

WikiProject class rating[edit]

This article was automatically assessed because at least one WikiProject had rated the article as start, and the rating on other projects was brought up to start class. BetacommandBot 10:03, 10 November 2007 (UTC)

Math error - dB(SPL) values do not match SPLs in Pa[edit]

The ratio of 101,325 Pa to 2 × 10-5 Pa is 97 dB, not 191 dB. What weighting is being used to get these values? -- Denelson83 16:10, 6 March 2008 (UTC)

An RMS pressure of 101,325 Pa (mean square pressure 10,267 kPa2) is equivalent to a sound pressure level of 194 dB re 20 μPa. No weighting is needed. Thunderbird2 (talk) 17:35, 6 March 2008 (UTC)
So then how come the article doesn't say to use the ratio of the squares of the pressure figures to derive the dB(SPL) values? -- Denelson83 19:32, 6 March 2008 (UTC)
There is a separate article about sound pressure level where that is explained. Isn't that enough? Thunderbird2 (talk) 21:38, 6 March 2008 (UTC)
I've just realised that sound pressure level links back to this article, which means that the explanation you are seeking is already here in sound pressure. Thunderbird2 (talk) 22:31, 6 March 2008 (UTC)
Oh, there it is. Gah, missed it! >:( -- Denelson83 03:01, 7 March 2008 (UTC)
No worries. I was convinced it was in a separate article myself! By the way there is a case for using 191 dB instead of 194 dB for the theoretical upper limit for sound pressure level in air. If you take the upper limit to correspond to a wave whose amplitude is one atmosphere, its rms pressure would be 1 atm divided by sqrt(2). When you square it that gives a sound pressure level that is 3 dB lower. That could be why 191 dB is preferred by some. In fact the whole calculation is dodgy because the theory of linear acoustics breaks down completely with such high pressures. For water (if also at atmospheric pressure) there is additional 26 dB to be added because of the difference in reference pressure. Thunderbird2 (talk) 08:03, 7 March 2008 (UTC)
191 dB does make more sense so I changed it. Per above reasoning. Thunderbird2 (talk) 11:59, 8 June 2008 (UTC)

Non-linear acoustics and shock[edit]

This article misleads. Shocks and non-linearities occur at SPLs well below 194 dB. And levels above 194 dB are possible. As Thunderbird2 says here "In fact the whole calculation is dodgy because the theory of linear acoustics breaks down completely with such high pressures." I think the whole section should be deleted until someone has time to put in a correct explanation. pheon (talk) 23:44, 26 August 2008 (UTC)

Yes, there are frequency/phase non-linearities in air at any sound pressure level, and temperature, altitude/barometric pressure and humidity have a bearing on such effects. I am not arguing in favor of deletion as I'm hoping some expert can jump in fairly quickly to give a succinct description. Binksternet (talk) 01:43, 27 August 2008 (UTC)

Underwater SPL reference pressure[edit]

The article gives the reference pressure commonly used in liquids as 1 micropascal, which is less than the reference used in air. However, Beranek's Acoustics gives a liquid reference pressure of 1 microbar, which is much greater than the air reference.

Is this a microbar/micropascal typo in the article? —Preceding unsigned comment added by (talk) 16:34, 9 November 2009 (UTC)

From a posting in the comp.dsp newsgroup almost a year ago (14.11.08):
"In water the reference is: 1 micropascal
Historically, SPL in water used to be referenced relative to 1 microbar which is 10^5 micropascals. So, the conversion from the old system to the new system is to subtract 100dB <> 10^5. "
David Biddulph (talk) 16:49, 9 November 2009 (UTC)

.356 PA doesn't yield 78 Db[edit]

Just to point out the bleedingly obvious, this article is self contradictory. is 85, not 78. —Preceding unsigned comment added by (talk) 08:21, 3 March 2010 (UTC)

I believe there are multiple errors of this nature. The problem is that most of the numbers are not cited so in most cases you don't know whether to correct the dB to match Pa or Pa to match dB. --Kvng (talk) 15:13, 14 June 2010 (UTC)

A-C Weightings[edit]

I have never heard of B weightings being used for certain SPL levels and there is no source. I cannot find any information which states this. I think its made up. ErikSorensen (talk) 11:51, 22 September 2010 (UTC)

I've marked[citation needed] that for you. --Kvng (talk) 14:00, 22 September 2010 (UTC)

This article is useless[edit]

I came in here from a link in the article regarding determining absolute thresholds in humans. I came with a simple question; "What is the generally accepted threshold of sound detection for human hearing". I leave, confused by formulas and micropascals with no idea of how they relate to decibels, or what the generally accepted threshold of hearing might be. This article is an excellent example of the cesspool that Wikipedia has become: editors creating monstrous articles out of contributions from experts, but the article does not have a target audience in mind, and instead becomes a firehose of information in attempt to be comprehensive. F-. —Preceding unsigned comment added by (talk) 17:33, 12 October 2010 (UTC)

I'm not sure what you were looking for makes sense. Can you restate what it is? 018 (talk) 22:53, 12 October 2010 (UTC)
I don't understand the question either, but the article Absolute threshold of hearing seems relevant.Dondervogel 2 (talk) 10:12, 13 October 2010 (UTC)
The second paragraph of the lede states (fairly clearly) that the generally accepted threshold of sound detection by human hearing is 20 µPa r.m.s. (for a 1 kHz tone). If you want to know what the threshold is at other frequencies then see the loudness article. This appears to be a simple answer to a simple question, so I'll make guess that it doesn't satisfy you because you expected an answer in dB. If so, then you need to know that decibels are not really a measure of sound, but of relative power; 10dB means 10 times as powerful, 20dB means 100 times as powerful, 30dB means 1000 times he power, 100dB means 10000000000 times the power etc. (unfortunately the decibel article does not make this very clear). Of course sound is often quantified in dB, but that's relative to the nominal threshold of hearing. So saying a sound is 30dB is just saying it's 1000 times as powerful as the quietest audible sound. On this scale the threshold of human hearing is 0dB by definition - but that's just saying the quietest sound you can hear has 1 times the power of the quietest sound you can hear. If it wasn't dB you were after, then you'll have to ask again. --catslash (talk) 12:37, 13 October 2010 (UTC)

Threshold for certain permanent hearing damage?[edit]

The table got levels that might be harmfull but not when it will always be harmfull, i would like to know that. --TiagoTiago (talk) 15:45, 25 November 2010 (UTC)

This is dependent on the individual. To know with certainty, you'd have to expose a large number of people to dangerously loud sound. Not something any researcher would do intentionally. Maybe someone in the military has studied such scenarios. --Kvng (talk) 03:46, 29 November 2010 (UTC)

Table of underwater sources[edit]

The source levels in this table should in most cases be referenced to the sound pressure level at a distance of 1 m from the center of the source (see ref. 12). This is usually an estimated value, since measuring the sound pressure level at this location is usually not possible. Genesis 1:3 (talk) 22:06, 27 December 2010 (UTC)

Good point. Source levels don't belong here, so I deleted the table. Dondervogel 2 (talk) 07:39, 28 December 2010 (UTC)
Why do you think deleting the table is the best solution to this? --Kvng (talk) 19:27, 29 December 2010 (UTC)
A table of underwater sound levels should be in this article. If the table needs a caveat or explanation, one should be provided. Binksternet (talk) 23:30, 29 December 2010 (UTC)
I agree that a table of underwater sound pressure levels would be appropriate. The table did not contain sound pressure levels, but source levels. Source level is a property not of the sound field but of the source itself (related to the source power). I deleted it because it seems misleading to include a table of (transmitted) source power in an article about (received) sound pressure. The values could be converted to an estimate of sound pressure level at some distance from the source, but that might be considered original research. Dondervogel 2 (talk) 10:40, 30 December 2010 (UTC)
Conversions are not original research, per WP:CALC. Have at it! Binksternet (talk) 12:19, 30 December 2010 (UTC)
I'm not convinced. If nobody makes tables of underwater SPL, why should we? Dicklyon (talk) 16:39, 30 December 2010 (UTC)
The conversions are not routine in the sense of WP:CALC, but values of SPL must be available from somewhere. I'll keep an eye out. Dondervogel 2 (talk) 11:39, 31 December 2010 (UTC)

Multiple sources SPL[edit]

Is the equation for calculating the sound pressure level from multiple acoustic sources correct? Consider the situation where there are two acoustic sources, which cancel out at at a point. At this point, there would be no sound due to the cancellation of the sources, but this would not be reflected with this multiple source SPL calculation, where the addition of the RMS of the pressure would give a non-zero value.

Should the RMS value not be calculated from the sum of the pressure sources at the point? — Preceding unsigned comment added by Citizenthom (talkcontribs) 10:34, 20 July 2011 (UTC)

The article refers to "The formula for the sum of the sound pressure levels of n incoherent radiating sources ...". The sources would cancel only if they were coherent. - David Biddulph (talk) 13:03, 20 July 2011 (UTC)

Sound pressure equations and Area[edit]

What is the area mentioned when converting between sound pressure, p, and sound power P_ac. Is it the total area of the wave-front? (I.e. a sphere at a given distance from an omnidirectional source). (It's under the heading Particle displacement, though I'm not sure why) (talk) 06:54, 15 February 2013 (UTC)

Why different symbols for particle velocity, and questioning intensity[edit]

The section "Instantaneous sound pressure--Intensity" says particle velocity is symbolized by (vector) v, whereas "Instantaneous sound pressure--Acoustic impedance" says "U is particle velocity" (actually speed, a scalar). I've just made the corrections. JKeck (talk) 06:08, 4 May 2013 (UTC)

And since when is intensity a vector? JKeck (talk) 06:10, 4 May 2013 (UTC)

Indeed: On the page about the loudness measure sone, intensity is referred to as a scalar, non-instantaneous property of a sound. So, are you sure intensity of a sound is an instantaneous measure? Assume intensity is an instantaneous measure, varying along a wave through space, and varying in time at a given spot: within a sound wave, isn't the particle instantaneous velocity zero at points of maximum pressure, and isn't the particle velocity maximum when the pressure is zero? At these two points, then, intensity would be instantaneously zero. Thus intensity is oscillating with twice the period of the sound wave itself. Maybe just me, but this seems fishy. Randallbsmith (talk) 23:17, 30 September 2013 (UTC)

Intensity is equal to the product of sound pressure and particle velocity. Particle velocity is a vector (and sound pressure is a scalar) so intensity is also a vector. Dondervogel 2 (talk) 06:10, 1 October 2013 (UTC)

200+ Decibal Sounds[edit]

There are incidents that have achieved to result a sound over 200-315 decibals.

1 Ton TNT Bomb: It would probably have a Decibal Count of 210.

Tunguska Meteor: Has resulted in generating 300-315 decibals

Anti-matter?: This can be irrelvant or impossible to happen. If anti-matter (1 Gram) were to collide with a "matter" area (e.g. gas), how much decibals of sound would it generate? Would it be 210 Decibals (1-Ton TNT) multiplied by 42960 Tons (1 Gram Anti-matter = 42960 Tons of TNT)? — Preceding unsigned comment added by (talk) 02:57, 16 June 2013 (UTC)