[thxgoon]

Sounds like an interesting build. Any reason you don't want to go bigger than a 12" driver? Do you have a budget?

Rythmik makes great subs and are an easy solution. DIYCable offers the Shiva X which is about as good as 12" drivers go at the moment. Two of those (ported if you can manage it) would do nicely.

Any possibility of using an external amp? Porting? I assume this is for home theater by the Z11 :R

 

[thxgoon]

Using the largest enclosure you mentioned the Shiva 12's in a sealed box will muster about 101db at 20hz, whereas the ported version tuned to 20hz nets you 110db!

The Audiopulse Axis 15 looks pretty good too. 107db sealed and 116db ported. Overall response looks pretty good with this driver too. Don't worry about designing a port, we can help you with that. For these examples an 8" by 3" slot port 40" long looks great.