REL Acoustics HT/1508 Predator 15" Powered Subwoofer; Black

"The REL gives the kind of Hi-Fi performance and depth to content below 80Hz which is ridiculously good to listen to. Also, because there’s so little group delay, it sounds like the bass is coming from the speakers themselves and not from separate subwoofers, perfectly in sync with the impulse response of the rest of the speakers.".