Bryan. It's just a reflex cab, nothing too special. The "overdamped" design is a function of the driver more than anything. I guistimate the internal volume to be roughly 5.0cu.ft. which is small for an 18" driver.
If you plug the drivers TS specs into a modelling program like WinISD Pro (
www.linearteam.dk), you can see the effects different box sizes and port tuning will have. The Pro version will also simulate power response so you can see how much power the system will take before cone excursion becomes an issue. The modeled response in WinISD and the measured response published in the project are close enough to be considered valid. I don' think any additional EQ would even be necessary, the system should provide fairly flat response down to 50hz all on it's own, and soak up 1200w without exceeding xmax. It will definitely make a compact and powerful sub.
P.S. The port dimensions in the plans tune the box to about 40hz, this accounts for the gentle rolloff in response as frequency drops. With this tuning driver excursion is exeeded at 900w. If you raise the tuning to 50hz,(make the ports 7.5" deep instead is 13") the system response is now flat and power handling goes to 1200w before excursion is exceeded. The tradeoff is steeper rolloff below tuning, but if maximum power handling for short term peaks is the goal, then this is the tuning you want.