Questions:

Do you already have a driver?

Do you have a target box size?

Will it be used with a solid state amp?

I would bet there is a Pi with your name on it. Most of the 15" Pi's could do well as a sub. Just delete the High frequency horn and crosover.

JBL = pricy but real good. downside is not so much deep bass, but what you get will be as good as it gets.

Eminence = cheaper, deeper and amazing sound for the money.

Then what size box can you handle, and hey maybe a cornerhorn sub pair to get the best bass and keep the horn theme going. Now im getting carried away. (one can always dream/maybe I'll build some next year)

Thomas