Sub-woofers to go with Quad 988 / 989 ?

Does anybody know of a really good sub-woofer that integrates well with the Quad 988 / 989 ?
Hi, I have a suggestion for you but first I want to clearly state that I am connected with the company whose product I am about to recommend. I am currently using a pair of Definitive Technology's new SuperCube 1 subwoofers with Quad 989s and the result is fabulous(in fact I was originally using 1 and the result was quite similar)I run the 989s full range and cross the subs in with their built-in crossovers at 40 HZ. The blending is superb and some very critical listeners who have heard them agree. In fact Jack Wright the US Quad distributor heard them and remarked that it was the best he had ever heard the Quads sound and that the sub(there was just one when he listened) blended perfectly. I normally wouldn't get on here to tout our products but I thought this was a special case.and I'm making my connection clear(unlike a lot of people who get on here and secretly tout their products or knock the competition). I hope this is OK.
Sound Lab B1. Dipole ES bass.
Check out the Art Of Sound Tycus, or Maximus sub. They even work with difficult speakers like Maggies, and etc. Their site is
I'm using a REL Stadium III. It works great with the Quad 988s, at least. The REL subs integrate well, and have power and finesse. Actually, though, in many rooms, you won't need a sub at all -- unless you just want to rattle floors and walls.
get yourself a good, sealed front firing sub w/ cutoff somewhere @ 100hz. i disagree w/ rel and other down firing subs as they're muddied per the downward firing driver..takes away the staging and the imaging (yes, bass images). good ones that come to mind are used entecs and audio physics rhea

i am using a pair of entecs w/ merlin vsm-ms (as fast as stats) to great effect. no other sub worked per the reasons above.

Rhyno: I owned the Merlins VSM-SEs and used a REL Stadium II with them. The sound was seamless and gorgeous.

Have you actually heard a REL set up correctly? And, no, bass doesn't image. You cannot tell where frequencies in the 20-60 Hertz range originate. Show me scientific papers that support your claim.
The only reason front firing subs would have an advantage is at higher crossover frequencies. Otherwise, when crossing at say 80Hz and down, downfiring subs will certainly not sound "muddied" if they are designed and built properly. RELs and ACIs are some of the most musical subs out there. Used properly.
The Quads are VERY difficult to mate with subs, because most subs cannot keep up with their purity and speed. I've tried Entecs, but their cutoff frequency was too high and the X-over well to put it mildly ruined the Quads sound. So NEVER, ever use the high pass out to go on to your Quads, rather let them run all the way and find a subwoofer which cuts off sharply at 30 hz, which is the solution, which I found. Was a bitch to place it right, but then the thing worked. Bobby Carvers Signature, you wouldn't believe it, but never, ever over 30 hz. Gradient had a sub made especially for the predecessor of the 988, which was quite nice, with the Quads placed right on top. I also used old Maggie bass panels with the Quads and let them run until about 100hz. Got a beautifull bass and cello sound that way.
bass does image above 80hz, and as far as i've heard, quad's do need a sub above 60 (up to 100 or thereabouts) to provide some impact and dynamics to the sound. x-over below 100(@ 60-80) will work, and probably easier, but you won't have much in the way of mid-low bass dynamics...that's the limit of the panels. and as jd97 points out, and correctly, front firing does(!) matter @ 100hz...but he's right in that from 60 down it doesnt.

and yes, the entec x-over just sucks. the best x-over i've heard is a passive RCA type x-over, ala audioconcepts (just a cap in line to the amp inputs), but made by TG audio...1st or 2nd order (forget which) at 100hz (custom built, @ $150), passive, and transparent...which few x-overs are. plug this x-over into your amp inputs, run the subs full range via a 2nd output from your pre, and the subs will naturally roll off @ 100hz (depending on the subs), while the x-over rolls off the mains @ 2db / octave starting at 100hz. works very well.

can't stress how important it is to get the last few hz...lots of stage and size comes with it. presentation just gets huge.

one more tip: elevate the sub, particularly front firing. even if its only a few inches, but better still if its 10" and up...decoupling from the floor reduces the 'muddy' aspect found in most subs...rosenberg mentioned this guy, gone too soon.

Seas Excel W26 + Hypex HS 200 amp. I'll post a review ASAP.