I've heard one 15 sound good in my life and it was in a dedicated sub-woofer enclosure. Other than that I've always been a 10's guy though 12's are really nice. The four 6.5" mid woofers are really nice, they don't pound but the base is so articulated and nice. Still need to do something about the sub. I was thinking about building my own mini klipschorn style thing for an 10 inch sub.