Best Subwoofer for Quad 2805 under $5k

Looking for musical subwoofer for 2 channel listening (Not home theatre!) that has the speed and finesse to keep up with Quad 2805s. Heard the Wilson Benesch Torus is an amazing combination, but don't want to spend $13k.
Thinking about the REL Gibralter G2 (carbon fiber driver) or the JL Audio Fathom f112. Has anybody tried these subs with the Quads? Any other thoughts?
check out the review of the VANDERSTEEN V2Q here in AGON
one of the fastest and most musical subs out there at any price

Review: Vandersteen 2Wq Subwoofer
Might want to take a look at the manepan bass unit:
Experiencing great results using 2 REL B2 subs with Quad 2905's. After much experimentation seamless intergration was found in my room by placement only about 3 feet behind the inside edge of the Quads and toed inward.

Room resonances were controled with cast concrete blocks under the Rel's (aprox 25 kilos) and about 5" thick. Cones are placed under the front feet resulting in a backward tilt.

A pair of REL B2 or B3 here on can be had well under your budget and 2 subs are better than one in my subjective opinion.

I havn't had any experience with the subs in your enquiry and don't doubt their application, but I've found subs are like real estate ,location , location, location .

Keep us posted on what you end up with and the results, very interesting.

I have used a pair of REL 505s and later the G1s with great success with the Quad 2905s. Superb subs, easy to blend as the G1s have a remote.
My recommendation would be a pair of Anthony Gallo TR1D subs. They are small and unobtrusive sealed cylindrical encloseure with a 10" woofer and a 200 watt amp. They are simple to integrate and do not produce ponderous bass. I use them with ESP speakers driven full range and the subs connected speaker line input and utilize the sub crossover. The ESP's are sealed and the bass they produce is tight and quick but not that deep. The TR1D's match perfectly adding the deep bass without bloat.
I never could get my REL B3 or the six previous subs to perform to expectation. The Gallo's do what I want and for only 1200.00 for the pair.
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Ime when it comes to low bass, the elephant in the room is the room. No matter how flat the subwoofer starts out, the room will superimpose its effects. We can change the room-imposed peak-and-dip pattern by moving the sub and/or moving our listening position, but we cannot make it go away. It is impossible to find a location for a single sub that provides approximately flat response in the sweet spot, much less elsewhere in the room.

Distributed multiple subs offers an elegant solution, each sub being in a different location and therefore generating a different peak-and-dip pattern, but the sum of several such dissimilar patterns will be vastly smoother than any one alone. Instead of a few big peaks and dips that are quite audible, we end up with more, smaller, closer-spaced peaks and dips, and the subjective improvement is even greater than we might expect because (at low frequencies) the ear/brain system will average out peaks and dips that are within about 1/3 octave of each other.

While it's possible to equalize a single sub to be flat at the microphone location, its response will be far from flat at other locations within the room. A distributed multisub system significantly reduces the spatial variation in response, such that the difference from one location to another is greatly reduced. If further EQ is needed, it is likely addressing gentle global problems, rather than acute local ones.

As a general rule of thumb, two subs have about half as much variation in in-room response as a single sub, and four subs have about half as much in-room response variation as two subs (assuming they're spread around somewhat). Smooth bass = fast bass, because it is the excess energy in peaks that makes a subwoofer sound slow (the ear/brain system having poor time-domain resolution at low frequencies, it is the frequency response that dominates our perception). Also, smooth bass = powerful bass, because we're likely to set the average level of the subwoofer lower than it should be if the response has distracting peaks that stick out like sore thumbs.

Dipoles have smoother in-room upper bass than monopoles do, so the discrepancy between two dipole mains and a single monopole sub is greater than what we get with conventional main speakers. If you read accounts of people who have tried subs with dipole speakers, it seems like most people who try a single sub eventually give up because they can hear the discrepancy. Most people who try two subs keep them, because they don't hear much discrepancy. Three or four subs would be better still, and they can be small subs.

I spent several years trying to design a super subwoofer that was "fast enough" to keep up with Quads and Maggies while offering good extension and impact. I tried sealed, transmission line, dipole, isobaric, aperiodic, and more. Then a conversation with Earl Geddes changed everything, and I'm now an advocate of distributed multiple subs, in particular for use with dipole mains. I'm using his ideas with his permission.

Imo, ime, ymmv, etc.

Ken Kreisel
An under-appreciated sub is the Martin Logan Depth i (and I assume the Descent would be aswesome as well, though I have not heard one). I have used either a single or a pair of the Depth i in my systems for years. They are very configurable, very musical, and fast, and I never had an issue paring them with any speakers that graced my system, including Eggleston Andras, Klipsch LaScallas, Zu Essence, etc. They also server dual duty for HT.

I'd be lost without at least one!
There are a lot of great subs out there. I use Rythmiks (they pair wonderfully with little Maggie panels), but SVS, HSU, and several others are also well regarded. I'd only offer a couple of general thoughts you might want to consider.

Think of "tight" rather than "fast" bass. IMO, You'll get to the same end and save yourself some headaches of mis-communication along the way. Tighter bass may or may not be better for your system/taste, but at least it makes sense conceptually.

Integration of subs can be executed in several different ways and may affect your choice of subwoofer. If you use room correction software, you may end up happy with a single, high quality subwoofer. If you use a more traditional, non-EQ approach, I'd think hard about Duke's multi-sub, distributed bass advice.

Good Luck

Depending on room size, I would recommend a REL T5. Very fast sub which works great with my SF GH's and I'm sure will work great with Quads.
I have had the Rel T5 with my Quad 2805's and the Rel T5 is surprisingly very good with the Quads. Very fast and satisfyingly deep on a lot of music. However, I upgraded to the Rel R328. The R328 is in a different league with a 10" active and 12" passive. Very Fast,very musical and articulate deep bass. I am very happy with the R328 with my Quads 2805. Well under the 5k. The Rel G1 or G2 would be worth an audition. You can't go wrong with the Rel Subs.
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.

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.