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Simon Bridge
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Jan19-13, 06:26 PM
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in the following article,the person who answered the question did not take [area of mouth opening] into account
It appears the author did - from the article cited:
80 decibels produces .001 watts of energy(sic)
... the intensity from the sound would be in watts per square meter.

80dB would be about 1x10-4Wm-2 ... so he seems to have used an area of about 10m2 ... which seems a little large. Perhaps the author has a big mouth?

The whole thing is suspect isn't it - I'm sure I can make myself heard in the front rows of a rock concert - well, by yelling in someone's ear.
If I yell at a cup of coffee the same intensity that is more like 0.1Wm-2. Figure a mouth area of about a square decimeter
(0.1m x 0.1m = 0.01m-2) and that's 0.001W directed at the cup.

So the final figure is about right.

ref. http://www.physicsclassroom.com/class/sound/u11l2b.cfm