Thanks for the interest in the Carnivore design. I did this in early 2010 for John's TD18H+ as a state-of-the-art pro audio subwoofer. For our performance target, we were competing with the Turbosound TSW218 (non-DP), a $5000+ box. The Carnivore is about the same size in front, but 8" deeper, so keep in mind that it is very large, and will just fit through a single door. Because it is a pro audio subwoofer, its corner is somewhat higher than most home theater subs, around 35 Hz. This subwoofer is designed to reinforce pro audio main speakers, which are usually most comfortable being rolled off in the midbass, between 55 and 75 Hz. The simulated capability of a single box (using Hornresp) is 140dB at 40 Hz and 142 dB at 85 Hz with 4000W available, so we met our performance target and exceeded the performance of the TSW218 by about 5dB at 40 Hz. However, if your intention is to use this design as a home theater subwoofer, you might be disappointed in its LF extension (which is a function of the design and not a limitation of the drivers themselves).
If it works, but you don't know why it works, then you haven't done any engineering.