[Tyson]

More displacement is ALWAYS better with bass   Dual 12's actually have more displacement than a single 15, and will also play a bit higher to match with smaller speakers more easily.  A single 15 is going to move less air than dual 12's and will also take up more floor space.  And dual 15's would be pretty damn massive (which would be cool, IMO).  But you cannot take a woofer optimized for a sealed box and use it in an open baffle, it will certainly not perform well.  You have to design it from the woofer for the OB application. 

[Rclark]

Good point. It would be pretty big with 4 15's. I'm gonna talk to the guy at Rythmik though and see what he thinks. 15's could potentially be even better because you would barely push them at all.

[mlundy57]

Like Tyson said, the 15" Rythmik drivers are not designed for OB use. Both the drivers and the amps need to be designed for OB.

If you are going to use two 12" drivers per side the SW-12-08FR (8 ohm) drivers would be the best choice. If you want three 12" drivers per side you need the SW-12-16FR (16 ohm) drivers.  You also need the OB version of the A370PEQ amp.

If you order through Danny you will get the OB versions. If you order directly from Rythmik be sure Brian or Enrico know you are building OB subs so you get the right versions.

I recently finished building a pair of the GR/Rythmik OB subs using three of the 8" drivers per side. The three 8's don't have quite as much presence as two 12's but work fine for my room. You're going to want the 12's with the Maggies. Two or three per side is up to you but you will want the 12's.

I agree with the comments so far about OB bass. I have the bass units mated to GR-Research OB LGK Wedgies. The integration is seamless. The sound is just right. Like one full range speaker instead of two separate units trying to play together but not quite getting it.

Mike