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Re: "This is completely wrong"


>That was an oversimplification - and the full unsimplified version that takes into consideration room modes, etc is unnecessarily complex in the context of the question posed.

If you want a useable simplification in typical rooms the best thing to do is to throw out the distance. Otherwise you're going to end up with an answer that's off by 6-10+ dB (implying you need 4-10X the amplifier you actually do).

I got curious about this once and measured my center channel (left and right speakers were actively tri-amplified dipoles which were too messy to make sense of). It took .88 VRMS to produce pink noise at 75dB SPL at my listening position 9' distant, which is the same thing as 75 + 20 log (2.83/.88) + 20 log 2.74 meters = 93.9dB/2.83V/1 meter sensitivity.

Since actual sensitivity is 90-91dB/2.83V/1 meter, the SPL at my listening position is what it would be at .6 - .7 meters distant.

This is in a not atypical 13x19x8' room with some openings to the rest of the house, the center channel on a short stand a couple feet out from the screen wall and no room treatments, just carpet, window treatments, furniture, and other stuff. The center channel was high-passed at 80Hz so most of the gain from front wall + floor proximity was outside the speaker's pass-band.

If you want an actual calculation that's meaningful, you need to start with room volume and Rt60.

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