Best Subwoofer for Quad 2805 under $5k

I have Quad 988s with Electrostatic Solutions' maximum current upgrades and the Mye Stands filled with lead shot which provide a great deal of firm bracing for the Quad's driving panels. With the upgrades and the stands, my 988s have better LF performance than when stock, but they still roll off fast below 40CPS and rapidly lose LF impact. I submit that this is the reason that Quads are thought to be "polite" and are not known to good with pop and rock. I recently got an REL S-5 and now have it partially broken in and fully dialed in. The S-5 is not distinguishable and calls NO attention to itself, irrespective of how much very LF information is fed to it. The 988 sound has not been compromised by the addition of the REL. The REL is dialed in at about 40 CPS (the control that does this does not allow precise measurements other than the start point at 7PM on the dial of 30CPS and the end point at 5PM on the dial of 125 CPS. I have set the frequency cap at 9PM which means that its output is severely curtailed above 40 CPS.) The S-5 is fed full range by the output of my amps, as are the Quads. Frequencies above 40 CPS are severely curtailed by a filter circuit in the REL that has no impact on the full range Quads. When the REL receives information that is 40CPS and below, the impact, the power and the high definition of the LF information seems to be coming from the Quads - down to 20 CPS. Now, my studded up 988s are quite good with pop and rock and are no longer "polite" in the negative sense. All sources of music now have a strong and tight LF platform, which with Quads is transformative. This what REL calls a sub bass speaker is highly recommended for use with modern Quads.

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