I am looking for dimensions to build a sealed box for one D612D4 Sub. The manual says a volume (Vb) of .875 cubic feet for a sealed box. When I do the internal dimension calculations, that box seems to be pretty small...even with the inner dimensions of 12 7/8 (H) X 12 7/8 (W) X 10 1/4 (D) it comes up to .983 Cu Ft and that seems small. Can anyone give me some dimensions for a good enclosure? I am using 3/4" MDF.