Best Big Sub? or duals?

As a Velodyne dealer, I'm going to recommend dual DD18's for that size of room as I have the most experience using these subs in that size of room. To be honest, I don't think a single sub of any caliber will get you what you want.

Other options are dual JL Fathoms or Triad Platinum Powersubs. On a budget, the HSU subs are tough to beat.

The G213 has a huge sweet spot as well as 2 F113's. For the money you may want to go with the two F113's. DD18's would be another great choice. I use the F113's because I felt they have great slam and extension with zero overhang. They look great and have a small foot print but play more like a bigger sub. Don't look at graphs, just go demo them if you can. Guys will try to steer you towards looking at graphs but in the end you either like what you hear or you don't. I have never bought a speaker based on a graph. I read reviews and posts and then try to find a place to hear them. The reviews are pretty much dead on with the F113. They are getting better as I put more hours on them too. The guy at HT shack shows a graph and it shows the F113 distorting at high spl's. Then in the forum he says the F113 is the best commercial sub he has heard. Go figure!

I own a single F113 and all I can say, WOW! There isn't anything it can't do. I have tried it in three different locations in my living room, none of them being where it should go (my living room is wierd), and it sounded amazing in all three positions. It is the one piece of my system that I don't think will ever be outperformed.
I can't even imagine what a pair of them would do!

Christian_coach, I agree. I have only one Fathom F113 for a couple of weeks now, but it blends in great with my main speakers.

You can hear the bass lines walk through the music.
Even older music has a defined bass line.

I have several other Subs that I use for HT, but the Fathom F113 is used strickly for 2 channel audio.

Highly recommended!

Value goes to the HSU. I would do 2 15's in that room, upfront near mains, possibly in center on front wall behind/near the center, run in mono (.1 channel). Better would be two Paradigm Servo 15's (musically even more accurate).
Other dual sub options available, obviously, (yes, I like dual subs for you, EQ'd, up front for best integration....FORGET THE SUBS AROUND THE ROOM TO SMOOTH RESPONSE WITH TODAY'S TECHNOLOGY - besides, it looks unsightly and cluttered around the room) but would likely run more for the quality. Earthquake dual 15's will run more, and not out-do the Servo 15's.
Did I leave any out?