They both use a B&C Neo 12 - don't remember #, but could get if its important.

Why two?

One is for the 25-50 Hz that the Summa cabinet size does not allow. This is a bandpass tuned to about 32 Hz covering about the octave mentioned. It has a very long port on a tall cabinet and thus has its output about five feet in the air - intentional to get it away from the floor. Takes a lot of power to drive - very inefficient, but adds a notible effect at VLF.

The second sub design, of which I have two, is also bandpass, same driver, but completely different design. This one is designed to cover a, 35Hz - 120Hz and is put into the LFE channel. It too is ver low efficiency - no tube amps here! These subs are located around the room. In my system, even in stereo, the LF are routed to the LFE channel, so in essence I have two speakers 50Hz and up (monopoles), two 35 - 120 Hz. and one 25-50 Hz. they were balance by measurements and tweeked by ear.

This seems to work in my small room, but does not seem to be required in my very large room. In the large room the single VLF sub with ported speakers works great.

The small room needs a different solution with subs placed around the room and a very well damped low end. This would be true of all small rooms.

Global solutions for frequencies above about 200 Hz. are possible, but below this the solution has to be matched to the room, and try as I do, I cannot find rules of thumb that work. Although bigger is always better - of that there is no doubt. But my home theater is small because of the sound proofing. I can use it anythime. The big hoowm upstairs is a 'cooperate with the family" issue. When I am home alone I always listen in the bigger room.