what type of subwoofer is good for ribbons

Since the only Maggies w/true ribbon drivers are the 3-series and the 20-series, you will be in a very good class of panel.
However, I'd skip the sub until you decide you really need it. The 3.6, soon to be 3.7 is pretty good while the 20.1 is very good. (for bass output).

Match a sub w/ panels? Cross over very low...near the lowest rated frequency of the panel. I cross over my 1.6s (not ribbon) at about 40hz or less.

setup is key. Also, for Maggies, you'll need a good amplifier. NOT because they are a bad load, but because of fairly low sensitivity. Make sure you have a large enough room to integrate larger panels and can place them into the room far enough....3 or 4 feet from 'front' wall, as a start.

My HSU Research sub has 2x ports and a single optional plug. I use the plug and run in 'maximum extension' mode. Good output is reached down to a usable 16hz...the lowest organ pedal note. Bass guitar, standup bass and kettle drums are all musical. The lowest octave of an Imperial Grand is real, in room.

Go audition the Maggies without sub and see if you can live without it. I'll bet that the larger panels can mostly do without.

Subwoofer design that integrates well with Maggies and Quads and such is something that I've been interested in for a long time. Briefly, after building a very wide variety of prototypes in search of a subjectively "fast enough" sub, I learned from Dr. Earl Geddes that the primary problem is the room itself, so that is what needs to be addressed. But I'm not talking about room treatment here; I'm talking about an unorthodox approach to subwoofing. First a bit of background:

Dipoles inherently have smoother room interaction in the bass region than monopole speakers do, according to a paper pubished by researcher James M. Kates. The problem with dipole subs is, they don't give you that chest-compression whump! that good monopole subs do because they don't pressurize the room.

The peak-and-dip pattern imposed by the room itself is arguably the single largest hurdle to natural-sounding bass. It can be changed but not eliminated by moving either subwoofer or listener. It can be equalized in one spot only; move a foot or two away, and the equalization may well have actually made things worse.

The solution I learned from Earl Geddes is to use multiple subs scattered asymmetrically around the room.

The more bass sources you have spread around the room, the smoother the in-room bass. The reason is, each will produce a different room-interaction peak-and-dip pattern, and the sum of these multiple dissimilar peak-and-dip patterns is smoother than any one alone would have been.

Therefore, in order to minimize the discrepancy in the bass region between the Maggies (two dipoles in the upper bass region = smooth upper bass) and a single sub (one monopole in the lower bass region = lumpy lower bass), I strongly recommend NOT using a single sub; rather, I recommend using four. If that's not feasible, two or three are still significantly better than one. And the more you use, the smaller they can be.

If you scour the internet for comments on using Maggies with subs, here is what you'll find: Many people who try a single sub go back to using their Maggies with no sub. But nearly everyone who tries their Maggies with two subs keeps them. My recommendation merely takes that trend one generation further, to four subs.

As for sealed vs vented and so forth, in general sealed subs synergize better with the room, but a vented sub can be optimized to actually outperform a sealed sub in this respect. When Magfan plugs one of the ports on his Hsu, he's probably addressing this issue by optimizing the sub's native frequency response to complement the room's inherent gain at low frequencies, which is well worth doing.

All of the above imho, ime, ymmv, etc.

Duke
dealer/manufacturer

Hi, Check out TBI subs, there is a dealer selling some demo's on audiogon. They are probably the best sub for ribbons that I have heard. They truly are different in their approach than most subs, just take a look at their website for how they achieve building subs that are extremely fast and can keep up with ribbons and other speakers that are usually hard to integrate a sub with. I have a pair of their smaller subs run in stereo with great effect!!
Check em out!!! Tish

Asymmetrical sub placement is good.....Very Good. I read the Harman white paper some time ago and that was one major conclusion.

However, not having deep enough pockets to afford even a pair of the modest sub I ended up with, I must rely on my wacky Asymmetrical ROOM.
8 sides, 2 of which are at 45degrees to the rest, while the ceiling is about 11'6" at the off center peak.
This room really helps and acts to break up bass modes which may otherwise be troublesome.