Yeah, I figured you were an incorrigible audiophile! 
Completely guilty
One of the most beautiful--and most frustrating--things about developing products is how hard it can be to determine when stubbornly persisting in an effort is
exactly what's needed to make a breakthrough, and when it's actually going to be a waste of time (or otherwise fail).
To this day I still get surprised how often concepts that were initially favored go down in flames, and unlikelier-seeming ones morph and combine and then surpass the early leaders.
Serendipity plays a key role with shocking regularity, too. Someone misunderstanding a sketch and thus coming up with a neat idea, a flip comment made in gest inspires a winning solution path, a random material grabbed for a mockup simply because it was in the box at that moment in time accidentally had useful qualities no one would have anticipated...
It seems counter-intuitive to get good sound from drivers driving into one another. Have you contacted Brian at Rythmik Audio to inquire about using servo subs in a ripole configuration?
I'm not the right person to attempt to explain how it works, but two drivers moving toward each other and squooshing air out through an opening about a 1/3 of their combined piston size seems reasonable enough to me. The rest creates the dipole-like front to back separation, as I understand it, but with less energy out the back.
I do find the inherent force cancellation of the opposed drivers very appealing, especially since my living room is suspended over air space (vs a concrete slab).
I asked Brian and he didn't signal any problems with the servo system working. Basically, he confirmed that it's an OB kind of construction, then confirmed that the servo would both work as designed and work regardless of driver orientation (up/down would be ok). However, he didn't say whether he knew or otherwise thought that the
acoustic results would be good, just that the parts would function (the drivers would go where they're told to go).
Eventually, you'll need to test your ideas by building a ripole servo sub and an H-frame sub so you can demo them in the same room with an NX-Studio on top.
You're probably right. I'd hoped someone would be like "Sure! I've tested 30 variations of this exact servo ripole concept. It's awesome! Here're the CAD files for the version that a dozen audiophile friends all found best in their respective systems and rooms, after which we had to commission a pair for each person to be build in order to avoid fighting."
Which may still be the case, but I haven't found it yet.
I may try posting in another forum or two. The problem is that as much as I'd love to fool around with this stuff, I don't have much free time to invest (busy job, active kid, house, physical activity, the usual) so was hoping to accelerate or eliminate the learning curve. I'm starting to consider which way to build a testing platform... particularly about how much variation to try to enable in the prototype (port dimensions/geometry, air gaps, etc).
The other challenge is that I don't have any of the other parts to compare the servo ripole prototype with, and non-endless funds.
I live near Berkeley, CA. Does anyone with at least H-frames happen to live within a couple hours' drive? Or maybe I could ship someone the mockup to test.
