Best Home Theater sub or subs for a large room

If you have the ability, the Infinite Baffle sub systems are the way to go. The is a forum called "Infinitely Baffled" that has tons of info, and I did it in my room, which is a couple feet narrower than yours. I used (4) 15" drivers in 2 manifolds in the floor, the bass is better that any sub I ever owned (Velo, Def Tech, Earthquake, etc.) for movies, and music. I use them all the time. The effect of the floor shaking is the best for movies. Anything else for a dedicated theater is not going to be as good, IMHO.
You will not believe it, and the total system, which included the 4 drivers, 2 pro amps, 1 xover, and the wood for the manifolds was around $1000.
Good Luck !!

I would recommend Velodyne DD18 to shake your nice room. I have been using it since October last year and literally, my neighbor has reported me of shaking his house at night!

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Get a used Velodyne DD-18. My room is huge, it is 22 feet wide 70 feet long with a 22 foot high ceiling. The Velodyne DD-18 brings the room to its knees begging for mercy. Fast accurate and tight bass. A real slam-bam earth shaker.
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Also check out the Vandersteen subs. One is better for 2-channel systems seamlessly blending low bass with the main speakers, the other model is more geared towards home theater. And both are well-built and reasonably priced. Widescreen Review magazine wrote a nice review a few years back.