Best Big Sub? or duals?

Look at the SVS PB13 U before considering anything
the Epik conquest as well. both have CONSIDERABLE output
I own an SVS PB13 and I would personally go with the ED A7-900, The Conquest or the Ultra if anything, Have no personal experience with them, danley as well.

I have an SVS PB 13Ultra in my 23x18 basement with carpet on concrete and it shakes(O.M.G) with great finesse, detail, dynamics, very low distortion & extension is unbelievable. Usefull tuning ports too......ALSO: I'm buying a Sistrum SP-101 stand for it to raise it up off floor as suggested by many. Can't wait ......buy 1, or maybe 2 and shake a city block.....It'll rip yrrrr chest apart too.....
REGARDS Bacardi

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!