The 18 inch Ultimax is a nice driver but wrong application imho. HT is fine (in fact excellent), so somewhat unfair in your comparisons.
I would encourage folks to try drivers that are designed for professional audio and then go for the swarm. I did the OB and Rythmik thing for a few years, then I discovered B&C, BMS and Funk. Quad subs. No bass that sounds like you are in a “submarine” and just as quick if not quicker than Rythmik. My comparisons were to triple OB12’s for each channel and even then, I felt the bass attack/punch was missing. Both setups did not boom at all. But the quad sub swarm won out on freedom from SPL compression and felt livelier giving music even more of a foundation.
It takes measurements and patience. Whether you go for Rythmik, OB Rythmik or professional drivers, you will NEVER escape the REQUIREMENT for proper measurements, room treatments and some EQ. It’s a fact and implementation is what counts! Not
blanket assertions that Rythmik and OB are the
end all be all!
I see both the swarm setup and OB Rythmik as the finest examples of state of the art bass but honestly the devil is in the details and the musical requirements of the end user. And whether the individual has the space to implement these designs is terribly important to consider. Enthusiasts of classical music (and orchestra) will more easily appreciate the spatiality afforded by OB Rythmik designs, while for nearly all other genres of music the Geddes/Toole/LeJeune swarm bass system is really the finest I’ve heard (and it’s damn good at classical too).
Different strokes for different folks but the strokes have to be well executed!
Single subs, and full range speakers? That’s prehistoric when considering bass and you’ll run circles in trying to make it sound right. It’s an acoustical nightmare!