Dialing in a pair of subs is quite tough, and I have not been able to figure it out quite yet. In some respects, using a single, dialed in correctly can be much more accurate than two, not so dialed in!
I run a pair of DD-18s and they seem to be pretty close to dialed. Not being a professional, I am sure there is alot of room (sorry for the pun) for correction. I will be trying to locate a JBL Synthesis professional to EQ my room with the SDEC, which should help a bit.
The DD-12 are incredible. I know several folks that run electrostats that use the DD-12. Slouch? Well, I suppose that depends on who/what you compare it to. The DD-15 and DD-18, for output levels and impact, sure. To a midfi levels of Paradigm, Sunfire (sorry guys, it doesn't compare, imo) and just about every B&W sub (I do like the older ASW-800) The DD-12 rips for 2 channel and HT.
Now, onto Aerial. I have owned / lived with Aerial SW-12 subs at least three times. Each time I used a pair as I have not felt a single can give me what the Velodyne subs can, so I ran them in pairs. The SW-12 is one of the best 3-4 subs I have had experience with. (Velo, Aerial, Rel, ATC, Earthquake (nice sleeeper here), Talon, and the others like Sunfire, Paradigm, Energy, HSU, M&K, etc)
My issue with the SW-12s are that in large passages (be it an organ or explosion) the excursion of the 11.7" driver is so much that the ports BLOW ME. On hot summer nights, it is a nice feeling, but the port shaffing noise and air does bother me. Now, at any other time, I love, love, love the Aerial. If they made an SW-15 or SW-18 I would be in as THE SUB!
One gets alot with the DD series subs. Ability to dial them in, they are incredibly quick, output levels unmatched, and their shape is much more appealing (though, in my case, 18's in any cabinet are imposing) than the older HGS series.
I am having Sound Anchors make the first Aerial SW-12 like stand for a DD-18 so they will have the platform in about 2-3 weeks. I will set the DD-18s on the stand and place a very heavy piece of custom black granite on the tops. This is the single largest improvement I have heard with subs. Placing something very heavy on top. Not sure why, but it has made a nice addition, appearance improved as well and when my cats use the top as a catapult, it doesn't ruin the finish (sm!).
Dan