I need help designing a bandpass for a 18" sub. I heard that this can be a very complex project. I have built tons of enclosures before but they have all been simple types.

I would really love this sub to sound like the old Sony SAW range which were...

-Deep
-Strong
-Warm

The main problem is I'm having trouble finding the specs for this old 18". Its a Earthquake speaker with a visable spider on the front. have had it for about 7 years now.

Any help would be appreciated