Soundstream Enclosure

I was wondering if there was a High Fidelity Ported Box Size (Gross Cu. Ft.) 3.16 enclosure premade(here are more specs http://www.soundstream.com/sub/support_wooferspecs.html).  I am getting one t4-12.  Or do I have to get a custom one built.

Also what does SPL mean when talking about woofers?  

 I have never been satisfied with pre made boxes, I have always made my own. with pre made boxes they are too generic and cookie cutter in design. so i would recomend either making one yourself or working with someone to design one to your specs. custom boxes are more expensive then pre made due to the man hours to build.

SPL= Sound Pressure Level,  in a nut shell, moving a lot of air.