The R-528SE has a 12 inch carbon fiber woofer as well as a 12 inch passive radiator, the combination of which gives a much stronger bass response. REL says that using these two in tandem provides the same bass as would a 16 inch driver on another sub.  You'll also find high-quality installer-friendly parts, like low level RCA and LFE.1 inputs that sport individual volume controls. The REL R-528SE will be available this month at a price of $2,800.