Talk:Sound intensity
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People seem to get confused by dB vs linear units. When you express sound intensity in dB (giving "sound intensity level"), the physical quantity being expressed is still intensity. dB is just a convenient way of expressing the relative intensity in a convenient, dimensionless form. It's like a change of units. Instead of expressing intensity in watts per square meter, you could express it in horsepower per square foot. Although that would be a strange choice, it doesn't change the physical quantity being expressed.
Note that sound pressure level also started out as a measure of power, not pressure, since the formula is 
, and p2 is proportional to the power per unit area of the sound wave. If the acoustic impedance were always constant, dB-SPL would be a measure of intensity, even though it is based on the pressure. Of course, the impedance is not always constant, so in practice dB-SPL indicates what the intensity would be if the impedence were fixed.
In practice, it is important to distinguish between dB-SIL, dB-SPL, dB-SWL, etc., because they have different reference levels and because different measurement methods may be implied by the choice of units. Obviously if you have a detector which directly measures pressure, it makes more sense to express the results in dB-SPL than in dB-SIL.--Srleffler 04:27, 28 November 2005 (UTC)
As I've said on some other acoustics pages - it's important to remember that sound intensity is a vector and sound pressure is a scalar. So it is not generally true to say that "If the acoustic impedance were always constant, dB-SPL would be a measure of 'intensity'" because one requires the specification of direction and the other doesn't.—The preceding unsigned comment was added by Richardng (talk • contribs) .
[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, and which article I should re-link the word to. Signal strength? Would someone with expertise help, please? Sanguinity 19:23, 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 pressure). Again, if a particular sense of "strength" is meant, please re-link as appropriate. Sanguinity 18:37, 25 August 2006 (UTC)
