jqp,
Yes, I've had my full system set up in 3 different locations. And yes, it does sound different. My listening room at home is rather small, about 14' X 17'. I've had it at my shop during our TAAS events (17' ceiling approx 50' X 50' ,close to 40,000 cubic feet in volume). And a friends house, about 16' X 35' with a sloped ceiling of 11' to 8', along the length.
At home, I have the walls heavily covered in skyline type diffusors, with homemade 2'X4' fiberglass bass traps, along with some big traps made from R-12 fiberglass insulation batts. I haven't measured the room response, but just by ear, it's pretty nice. The biggest(readily noticeable) impact was the large fiberglass batts. It really tightened up the bass, and it's much cleaner now.
In my shop, we surround the listening space with (24) 30" X 72" Eckel acoustic panels with a perforated metal face, with 2" rigid insulation, and put carpet down on the floor.
In the third location, there was no treatment at all, and the room was pretty bare. It's not really worth discussing. It was too live a room, with a long decay rate.
The difference in the large room is that the mid range is a bit fuller, and has a little more weight. We can space the speakers quite a bit wider, the sweet spot grows a little, but the center (phantom) image is really, really good. It's like there is a center channel.
Room loading effects are( I'm going to say), not there. The overall effect seems to be a more effortless presentation. The system still gets plenty loud, even sitting back 15' from the speakers. The speakers do the disappearing act really well here. High frequencies are smoother, and the subsonics are more detailed and cleaner. It's like there's not as much congestion in the bass region, but more space between bass frequencies. The big room, is a big deal. It's easy to get totally lost in the sound.
Man, it's really nice, but honestly, I don't think I could accurately describe it. But yes, there is a substantial difference in a bigger room, and it's all for the better. I can't think of one negative in the larger space.
Cheers