Which subwoofer?

Kenrus, it is a double edge sword. You will need two subwoofers of at least 12". Yes, I did see the size of your room. If you are going to spend money don't bunt. You need two 12"s or four 10"s or you are just adding a woofer on top of woofers. Getting them to sound right under the MLs will be a challenge from an analog perspective, relatively easy from a digital perspective. Digital bass management IMHO is the best method of integrating subwoofers. 

@lewinskih01
I have a dual opposing subs as a single sub. Like you I am interested in Rhythmik pair of speakers to make a DBA, possibly open baffle as well?
Something to consider after I've got more room treatment finished.

@bdp24
I'd like to know more about the differences with sealed and OB with the Rhythmik sub amp designs. I wish I could hear both to make a determination, but not likely to be anytime soon.

@rixthetrick: To read lots of discussions about the GR Research/Rythmik OB/Dipole Sub, head over to the GR Research Forum on AudioCircle. There are threads dedicated to the sub which contain info provided by GRR owner/designer Danny Richie, as well as guys who have built it. Once you have heard an OB woofer, sealed/ported are simply no longer good enough!

Rythmik's Brian Ding does not actively promote the OB Sub, though it is listed amongst the DIY/Custom models (not just the OB, but also sealed and ported subs.). On the Rythmik website, owner/designer Brian provides a LOT of info about the Rythmik line of subs, some of it very technical (Brian has a PHD, and is brilliant). On the website there is also a link to another Forum with a dedicated Rythmik section. Rythmik owners are passionate about their subs! 

SVS

@bdp24 - thanks.
I know oldhvymec loves his OB too.

@oldhvymec - have your well fed chickens started laying Emu eggs yet? They are large and dark green, thought I'd share that, might save you puzzling over it in the future if they do :-)