A lot of us, including myself, have been stuck with being overly comfortable with just placing subs on each side, the same way we do without tops, facing out. It's time for use to start trying some new things with placement.
Anyway, I started out months ago, by just putting one on each side, facing out. That worked fine. Then, when I decided I wanted to play with it more, I decide to try having one on each side, but each loaded against the wall. This sounded better, and I got an increase. Then, I coupled them, and loaded them against the wall. Sounded like a friggin bass machine. I have left it that way the last few times. Then I got reading in Bills forum, and he added a diagram for loading against a wall, for the T24's, but it applies to all Tubas.
http://billfitzmaurice.com/phpBB2/viewtopic.php?t=398
So last night, I decided to try this "W" configuration out, loading against the wall, to see how much of a difference it made. I almost crapped a brick.
From just two Tuba 30 Slims, I was a little scared by the levels loaded this way. It was a bit uncomfortable near the back of the room, from the levels of bass produced this way.
Making use of loading against walls is hugely to your advantage folks. Try it.
As for the Tuba 30s, I was using 18" loaded subs, of a DIY variety previously, but I have many years of experience building such cabs, and in every 18" loaded cab I have built, I've used some hefty drivers with excellent specs. Tuba 30 easily outperforms them, and now loaded with the Definimax 4012, they are monsters. To be honest, a Tuba 30 is bigger than any single 18" bass reflex cab I've built, but weighs about the same. Performance however, is no comparison. It would take atleast four 18" high end subs to compete against my two Tuba 30s at the 1 meter away competition, maybe more, but at 20 meters, forget it, Tuba 30's would eat those 18" subs.