Which subwoofer?

@bdp24 

You got me interested! :-)

Which GR Research Kit do you use? The one with 1, 2 or 3x12" drivers per amp? How many in your room? How far away from the walls do you have them in your room?

I have a couple of Rythmik F12 in DIY sealed heavy boxes, with the same plate amp GR uses (A370PEQ), although with the aluminum driver. I've gone deep into DIY speakers and I'm running open baffles above the subs (65 Hz). I was thinking of eventually adding another pair of F12 to create a DBA, but maybe I get a couple of these plate amps and more drivers and have open baffle DBA...

@bdp24 

Thanks for the perspective! I will do some digging at Audiocircle.

In my case my dipole (naked) 18" midbasses go from 65Hz to 275Hz. I agree there is some weight loss (vs a sealed 18") but I have not heard this level of articulation before. Large midbass, though!

I noticed you xo your GR Research subs at 180Hz. What's your view about how much difference it makes to have sealed vs OB subs below 70Hz? I'm sold on the advantages on dipole above that, but wonder if taking the sealed sub DBA below 65Hz wouldn't be the most practical approach and deliver the same sound quality.

@oldhvymec
Not familiar with what VMPSs bass is. I believe you are also into DIY OB speakers. I'm also running an active system, so no passive xo parts between amp and corresponding driver. I couldn't be happier. Currently a 4-way active stereo system...although I smell bdp24 comments might be leading me to a 5-way ;-)

@bdp24 

Danny Richie uses a pair of OB subs in the front of his room and a pair of F12G's in the rear (in both his company's listening room and at hi-fi shows), the F12's in phase opposite that of the the OB's. I believe he uses 40Hz as the x/o frequency between OB and F12.

This is great to know! So he's using F12s up to 40Hz. Do you happen to know how high he crosses over the F12Gs?I guess I have some chewing to do: I run F12s to 65Hz and from there unbaffled dipole 18", so kind of similar to Danny, but he has servo dipoles above the F12s. 

@bdp24 

Thanks again. You are right I was misunderstanding what the models implied. I totally get the F12 since mine are F12-like in heavy DIY sealed boxes. I thought the F12G were paper cone and open baffle (like Danny's designs), but I see on Rythmik's site they are sealed. So let me rephrase and provide perspective for what I was saying:

I though he ran F12 up to 40Hz, xo to OB subs (his Kit 4 or 5) from 40 to say 180Hz, and then xo to another driver. I guess my thinking was biased by the way I set up my system. And I know another user who runs multichannel stereo and used F12s (to 50Hz) in such a fashion with F8s above (frequency-wise) to 175Hz and JBL M2 above, so I though Danny was doing this but on OBs. 

I totally understand why he does it the way you describe it too: below 40Hz he gets 4 sources playing (F12s and OBs) so a DBA. Worth noting Earl Geddes argues for 3 or 4 subs and says the 3rd and 4th subs don't need to be as powerful, which in Danny's case would be the OBs below 40Hz. Then Danny gets OB bass with servos from 40Hz to whatever he xo, and let a regular driver take it from there. Makes a lot of sense and would demand a redesign of my system because those F12Gs would replace my dipole 18" but would not reach as high and the smaller surface (2x12" vs 1x18") I guess would be perceivable. In my prior iteration I had 2x10" in the midbass and the move to 1x18" was a significant step up in impact of bass while also having dipole texture (of course an 18" in a box would have more impact than it in dipole). Maybe I need the 3x12" GR Research :-)

Good food for thought!

BTW: do you place your OB subs close to the side walls? In my case I would need to, maybe 4 or 8" from the side walls in the front corners, 2 or 3 feet away from front wall...not ideal distance to front wall, but space constraints. I wonder if being close to the side walls would further detract from them.

@noble101
Indeed,Earl Geddes has said that subs has been enough for him, but 4 is better. It's important to note when Geddes talks about "better" bass he's referring to seat-to-seat variations across the room. So bass is more Eben across the room. He isn't talking taut, 3D-like, fast or other descriptors often used for "good" bass.

@iananderson
I know of a guy using Quad 63 and 3 Gradient subs who is looking into GR Research OB subs with great interest. I have not heard his setup, but FWIW he's a professional bass musician at Lyon's opera...his understanding of how natural bass sounds is surely better than mine!!!

Closing this loop in case someone in the future is interested in OB subs. I exchanged with several folks, some very knowledgeable in OB.

Danny Richie used sealed boxes in the back of the rooms at some audio shows to prevent large seat-to-seat variations for the audience. He doesn't use these himself. He recommends his OB, period. And if one wants to complement up to 30Hz with sealed he's good and in fact has recommended doing so in some cases. Danny does recommend 4 feet from the front wall, which is too much for my case (maybe I could get to 3 feet...)

I learned that when using OB subs it's very important to take your room dimensions into consideration, especially your front-to-back distance between walls (since dipoles radiate little to the side walls and ceiling/floor). To properly get to 20Hz you need that dimension to be 12 meters. My largest room dimension is 10 meters, close enough, but alas, my speakers are firing along the 5 meter axis (width) and for practical reasons I can't turn them around. 

So I'll drop the idea of adding OB subs and add another couple sealed servo subs. And a MiniDSP 2x4 to apply multi-sub optimizer to allow delaying any of them as needed and other DSP for individual subs. Then the overall DSP will treat the DBA/MiniDSP as a "unit".

As to what drove Geddes to set up distributed bass arrays, I'll pass and let people do their reading. Geddes was proposing his approach well before 2014 and his papers and videos talk about minimizing seat-to-seat variations. Surely more subs provide more, pressurize the room more, etc, but that was his main driver. He also doesn't (or didn't at the time of the videos) believe time-alignment between subs and mains mattered, yet others do.
Toole gets into it too in several places. His chapter 13 in Sound Reproduction gets particularly into distributed bass arrays with time delays among subs for optimal results. This does require measurement equipment, a learning curve, and spending significant time to achieve the results. In my view Audio Kinesis are a great solution that simplifies the approach yet retains most gains for those who aren't interested in going that far in adjusting time and other variables. A great solution indeed!
Not interested in getting into a debate about this, though. There are plenty of materials online and Earl participates in some fora for those really interested. I realize there will be one/multiple replies to this, but really not interested to debate and won't engage. 
Cheers and happy listening