The information was very helpful. I will try to read more on the SPL. Is there a recommended dBSPL at the distance where one sit and listen?
The reason I posted my original question was because, I was looking at Hsu website and they have 7 speaker packages deals (Sub+L+R+C). Each of these packages mention the room in cu. ft. it is suitable for. Some up to 2000 cu. ft. Some up to 3000, 4000, 4500, 5000 and 6000 cu.ft. Going over it in deal an hour back, I found it interesting to see that for all these 7 packages, the L+R+C is same and the Sub differs (its power increases as the room's size increases). So is it the power of the Sub and not of the L+R+C that matter when the size of the room changes?