Decibels and Watts

[shaunnutley]

If a human shouted at 100 decibels and this was measured at 1 foot away how many Watts would this be the equivalent to?

[Peter Pedant]

I thought a bel was a ratio of two phons

bel phon and watt are CGS units

and powers go around in watts/sq cm = still a CGS unit.

and a foot is FPS unit.

watts/sq cm is pressure you pling an ear drum at, and you are talking about watts as output of an amplifier

completely different,

I think I might let abother person have a go at this.

[Peter Pedant]

http://hyperphysics.phy-astr.gsu.edu/hbase/sou nd/phon.html

is a start

[Peter Pedant]

or.....

http://en.wikipedia.org/wiki/Phon

basically 100 db at 1000hz has a differnt loudness to 100 db at 2000 hz

[Peter Pedant]

oh!

the calculation is done here :

http://en.wikipedia.org/wiki/Decibel

see undeer examples -

it converts a milliwatt into a bel.....


and then and then, say it is 5 W

then a foot away is a sphere of 4 pi (0.3)2, isnt it. a foot being about 0.3 m, so say that is 2 sq m

then the power is 5/2 w per sq m

[mibn2cweus]

The total acoustic power produced by a 100db source is 10mW.
The amount of power absorbed at one foot depends on many factors including the surface area, angle of incidence, as well as the absorbency, transmittance and reflectance of the surface.

[Gef]

For Peter Pedant - the watt is an SI unit.

For info on decibels see here.

http://en.wikipedia.org/wiki/Decibel

[tubeway]

It also depends what sort of decibel you are talking about - dBSPL - is pure sound pressure, but dB(A), dB(B), dBHL (hearing loss - which is what I use in my career as an audiologist) are all weighted scales