Best Subwoofer for Quad 2805 under $5k

Vtman-

REL is the best sub period! Any model will do in your system, especially, the "T" series. Even the older models are simply outstanding. Keep me posted & Happy Listening!

The Finnish company Gradient made a dipole sub for the Quad 63 in the late 70's, I believe it was. it was a pair of 12" woofers in an open baffle H-Frame, the woofers facing in opposite directions and wired in opposite polarity. At least theoretically this is a design well suited to use with a dipole speaker.

There is a sub design currently available just like the Gradient, but using servo-feedback on the woofers. The plate amp with servo circuitry is made by a company in Austin, Texas named Rythmik (Martykl mentioned his sealed Rythmiks above), and the 12" woofers are a collaboration between Rythmik's Brian Ding and well know speaker designer Danny Richie of GR Research. The sub is offered as a DIY kit only, the user needing to make (or have made) the H-frames into which the two (or three) woofers are installed. Anyone wanting dipole subs to mate with dipole speakers should definitely check out the GR Research website for more info.

The JL subs will work well, but you might want to consider the latest BalancedForce subs from Martin Logan. They are designed to integrate well with their electrostatic speakers and retail at $2,995 (210) or $3,995 (212). With their optional Perfect Bass Kit (PBK) you can optimize your setup using the provided mike and software with your PC.

for music, rel g1

The problem is not the subs but the room. Hence use multiple small subs and dsp room eq like the DSPeaker 8033.