There's a new flagship from REL – the R-528 Special Edition. This new subwoofer improves on the 528 thanks to a handful of upgrades and a smaller overall footprint. You'll find similar tech to what's in their higher end Gibraltar G-1 system.
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.