Jason, the question of how loudly a speaker has to play in a certain situation(and the related question of how much power is needed at the time)depends on both room size and reverberation time and listener distance. A key concept in this is the "critical distance" of the room, which is the distance at which the sound level reaching the listener directly is equal to the sound level reaching him from room reflections, i.e., with both equal, the total sound is 3dB higher for the listener. A simplified discussion of this is found
here , with the formula for calculating the critical distance(in meters)with a certain room volume and reverberation time(typically about .5 second at mid frequencies for home listening rooms). Linkwitz has a more complex discussion
here in sections C3 and C5 to similar effect. The net result of this is that in typical home listening rooms the critical distance isn't far from the standard 1 meter distance for speaker sensitivity ratings, resulting in an "in room" number about 3dB higher.
Beyond the critical distance the contribution from the room reflections remains relatively constant at home distances and the overall sound level falls much less than the 6dB per doubling of distance that the direct sound theoretically falls. This is the reason that some of the power calculators available online are quite inaccurate, since they use the 6dB loss figure. Dr. Toole makes a similar point in his new book which was the subject of a thread here a couple months ago and which I'm reading now. At pp. 44-48, he discusses with illustrations the fact that sound level drops much less with distance in listening rooms when the room gain is taken into account.
So, the bottom line is that the calculations can get quite complex when all the factors are entered, but the requirement for speaker loudness level(and required input power)is less affected by both listener distance and room size than is sometimes imagined.
