My speakers have two 6" TL drivers per side, and a ribbon, and I augment them with an EQ'd 15" sub in my 24' x 20' room--but that's a personal choice. I listen mostly to rock, pop, and old-school R&B and country, and my combination of speakers/sub delivers a decent amount of impact in my treated room. But I think the choice depends a lot on room size and listening preferences.
