Arthur is right - big rooms need lots of powerful bass reproduction - very expensive as loud accurate bass is exponentially expensive. So the sound is indeed far better in a large room provided you have the resources to fill it with sound at necessary high SPL.
The one downside of a large room is long reverb times in the bass...you need plenty of LF absorption on surfaces and soft furnishings to keep this down (wood walls help leak out bass whilst concrete can be bad)....think of how lecture hall or brick gymn sounds awful(this is obviously far to big and too reflective)
My guess is that around 25 to 35 foot dimensions make a good large room with significant improvement over 15 feet. After this improvements diminish and eventually too large is bad....some wall reflections are actually pleasant remember that speakers outside in the open air sound hollow.
The one downside of a large room is long reverb times in the bass...you need plenty of LF absorption on surfaces and soft furnishings to keep this down (wood walls help leak out bass whilst concrete can be bad)....think of how lecture hall or brick gymn sounds awful(this is obviously far to big and too reflective)
My guess is that around 25 to 35 foot dimensions make a good large room with significant improvement over 15 feet. After this improvements diminish and eventually too large is bad....some wall reflections are actually pleasant remember that speakers outside in the open air sound hollow.