The inverse square law works in open field but not in a room. If you have a sound meter you can find out for yourself. You are right in saying that "this will change +/- with more/less absorptive acoustics", but in terms of the in room distance effect the change is invariably on the favorable side. How much room gain you get depends on the geometry of the room. In my room I do not lose much at all from 1 meter to 4 meters. There is no question that in open field one would need tons of power but in a room of say 12X20X8, I would take a $5,000 Luxman class A 20X2 amp any time over a $1000 200X2 class AB amp just to satisfy my curiosity. I am not not sure if I can hear a difference but I am confident the 20W class A will do fine in a small room.
I only used that as an example but some people do have very dead rooms, and while it's rare, that is a consideration when designing a system.
I have TrueRTA software on my laptop and it has SPL measurement. My room is fairly inert, because it was so bad before I re-worked it in '02. No more flutter, the sound is diffused and there are several places where the reflections are broken up, instead of causing standing waves. Not perfect, but my speakers disappear pretty nicely. My 100W/ch ES integrated amp does a good job of filling it with the volume control at about 10:00. When I connect my Conrad Johnson power amp to the pre-amp outs I had created, it's a sweeter sound and not quite as loud but still sounds fantastic because it's not a huge room.
You're right- room surfaces and geometry have everything to do with whether any equipment will sound good, bad or in the middle. That's also one thing that completely baffles me about this industry, at least, in the Milwaukee area. We have some pretty decent shops here and almost no attention is paid to acoustical treatment. I ran into an old customer last year and his ex-girlfriend had one place install TVs, cable TV jacks and distributed audio, but she was very unhappy and complained, held money back, said she wanted to return everything, etc. I went there and listened to it. They were right- it sounded terrible but I really didn't need him to turn it on to tell him that it would. Big, open floor plan with high ceilings, hardwood floors, lots of windows, very little furniture, no window treatments and no rugs or carpet. The speakers were ceiling mounted and in one corner of this big space, they had a stereo with a ton of power and medium floor standing towers. All they did was complain but they have no idea why it sounded as bad as it did and if they had come to me, I would have told them up front that it wouldn't sound good unless they decorated the place and put something in that would absorb the sound. That place had an RT60 in whole seconds.
Class A amps definitely have a sound of their own. Pioneer had one in the mid-'80s and for 35W/ch, it was sweet. The 200x2 will be louder but that's not really the only goal, anyway.
