Not sure if this helps at all, but it does sound about right, 2.25 cu.ft. found here at :

http://www.cardomain.com/item/ORIHCCA12D

The enclosure should be tuned between 30 - 40 Hertz for it to shake the ground the right way, plus it sounds amazing at those frequencies. I would try out 35 first and from there you will see if you can go lower or higher. Also, I have had some success with slot ports usually around 3" wide so I would also give that a try.

Do you need help with the building of the enclosure? Practice using WinISD Pro, as long as you can find the Specs on that subwoofer WinISD will help you with everything you need.

WinISD Pro can be found here :

http://www.linearteam.dk/default.aspx?pageid=winisdpro