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Acoustic Power Question

Acoustic Power Question

Acoustic Power Question

(OP)
This is probably an easy question for anyone who deals with acoustics regularly..
I'm trying to estimate the amount of power required to drive a speaker(s) which will produce 80dBA at 7 meters - radiating in every direction.
Seems easy enough to calculate the acoustic power from a point source using the inverse square law - comes out to 0.062W for 80dB @ 7 meters.  
Even with a really low efficiency speaker (say 5-10%), I know it is going to take much more power to reproduce that amount of sound from an amp/speaker.  
What am I missing here?

RE: Acoustic Power Question

Nothing really.  "Typical" speakers have efficiency ratings in the 88 - 100 dB/1 watt/1 meter, so your spec does not seem hard to achieve.

BK

RE: Acoustic Power Question

1/16 of a watt?
Yep,  that's what my calculations show: speakers aren't really all that efficient.
And,  a little sound goes a long way.

RE: Acoustic Power Question

And of course, over a certain range of frequencies, the radiation from the speaker is hemispherical (if it is mounted in a cabinet) so you get even more bang for your buck if you are standing in front of it.

M

--
Dr Michael F Platten

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