what frequency do i tune my enclosure to?

Well then, it looks like I'll be buying a new sub after all.  I've always loved JL's, so I might as well spend the extra dough.

Gentlemen, I really appreciate your time and comments.  I will look into the program suggested by stevdart (sorry, dude, didn't mean to wiz you off).  I'm taking your posts as, I should tune to ear.

Thanks again.

You're welcome.  :)  I get cranky now and then in my old age.  JLs perform best in sealed enclosures in just about every case, so building it should be a lot easier.

As you can see, in every case of a vented box question we want to look at the driver in question, the size of the space available, the power to be applied etc.  There are no short answers.  I've spent a lot of my free time over the past three or so years studying everything I could find (and there IS a lot to be found) on bass reflex enclosure design.  I would say I'm just now to the point of starting to get it. 

Sealed is much easier and in many cases the best box type to use (e.g. JL).  The old Crunch demanded a vented box, though.  The Xmax was a problematic concern in such a large box, but it would not have had any low extension whatsoever in a sealed box.  The graph I posted a link to (earlier post) was taken from my WinISD workup and shows a pretty decent response, almost akin to a sealed box response.  The problem was power input which might have to be kept reasonably at 200 watts or below.  Here is a cone excursion graph from the same program model showing what happens when given 300 watts ( but keep in mind that the parameters you gave are iffy, as I protested earlier ):  crunch_procast_cone_excursion_300w.jpg

The response, centered at 60 Hz, rises above the 6mm Xmax to about 8mm.  That indicates that the woofer will bottom out with that much power applied.  A smaller vented box could solve this problem but the sound quality would suffer greatly, with a poorer, more abrupt response curve.