Unless your main speakers are capable of faithful ~20hz reproduction, yes a sub will help. In my experience imaging, and overall accuracy improves no matter the size of the room. A good sub can be tuned to fit, though selecting the sub with the room size in mind is a good idea. IMO it's more important not to have too small a sub, than to have one too large for the room. One that's too large can be attenuated using the volume knob.
will adding a subwoofer improve overall audio
hi. my question is: will adding a subwoofer to my audio system improve overall performance, soundstage, clarity, etc. my system is: jm labs focal 918's(8' triangle between speakers, and away from listening chair), bat amp and pre amp, rega saturn cd player, running springs power conditioner, jps audio interconnects, kimber kable speaker cable. i have a small listening room, and am thinking the sub would help. also, any sub recomendations? i'm thinkin rel, jl audio, or b&w. thanks for the input, gil