Talk:Sound pressure

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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 = \frac{F}{A} \ \mathrm{ \ or \ } \ \frac{F}{S}
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

1 \ \mathrm{ Pa = 1 \frac{N}{\, m^{2}} } = 1 \mathrm{ \frac{kg}{\, m \cdot s^{2}} }\;

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

"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)

--- 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)

Contents

[edit] Strength

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)


[edit] Discrepancies in the SPL table

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.

75.26.195.139 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)

[edit] WikiProject class rating

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)

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

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)