I recently built a sealed subwoofer using the Creative Sound Solutions SD12 and am very happy with the results (I will post more on this in a couple of days). Originally, I tried to build an LLT with this driver, but in the end was not able to pull it off.
http://www.creativesound.ca/index.html
However, it appears CSS will soon have a 15” version of this driver with XBL to boot that should be able to pull of the LLT. Below are the target parameters for the new driver. My understanding is this driver will be available next month sometime.
Re: 3.60 ohms (1.8 ohms per coil)
Le: 1.80 mH
Fs: 19.2 Hz
Qms: 3.65
Qes: 0.44
Qts: 0.39
Cms: 0.25 mm/N
Mms: 274.8 g
Vas: 218.44 l
Sd: 790 cm^2
BL: 16.5 N/A
SPL: 87.3 dB@ 1W/1M
Xmax: 30 mm