JL sealed enclosure

1.25 cu.ft. is what I would go with for that sub. Remember to adjust for speaker displacement.

And remember to allow for material displacement. If you built your box 12" x12" x12" it would be 1 cu.ft. on the outside but will be quite a bit smaller on the inside. You box volume needs to be a net internal volume. I also would go with 1.25 cu.ft. for this sub.Top Secret, I can tell you but then my wife will kill me.

Do as Forbidden commands!  *and add polyfill*

Im using a site that has a "box calculator", it allows me to enter in the thickness of the material I plan to use. 1.25 it will be, Thanks. What will happen if I made the box to .90 cu? Would it just sound crappy?Thuan

It would sound less then its best...  .9 is a absolute minimum box size.  And the other number is a maximum recommended box size, above that they recommend a ported box.  JL ranks its recommended enclousure sizes with a letter grade, remember in school?  A, B, C, D, F.  Go see you local JL dealer to get a letter grade for your box size, but I think 1.25 is a very good number from my experience.  Remember to add the displacement of the woofer. So the number will really be like 1.45 or something.