Unfortunately, not much. My wife thinks the RF-35s are bass enough so I think a 15" subwoofer is out. My loft is only 144 sq ft (12 x 12) so maybe a Klipsch 10" subwoofer like Klipsch Reference R-10SW 10" 300w Powered Subwoofer? Will that be a noticeable difference than having no subwoofer and just RF35s? It's only $219 on Amazon with 5 stars and 998 ratings.