Help with RSS315HF-4 12" & LT ckt

[Marzen]

I wanted to incorporate two methods I've been interested in, using mostly left over parts. So I thought I'd have a run at a LT sub with curved sides.
I'm having trouble with the LT part in regard to calculating my initial target enclosure size even before applying the LT circuit. Is there a walk thru on the web for this?
I think I'm shooting for a flat ~70% max excursion from 20hz up to around 40hz in an attempt to end up with a critically damped Qb with extended bass response while using a small enclosure that would normally have a high Qb response peak.
Parts on hand are...
Dayton RSS315HF-4 12" High Fidelity Sub woofer
Rythmik Audio A250 watt Amp - Basic
Add on parts..
Rythmik Audio Half Installed Linkwitz Add-on Board for A250 amps

I like the look of this Phil Jones cab...
-Ward

[nayr]

That IS a nice looking cabinet. It also looks like a lot of work to build! 8)