I think this is the best place to post this question. I'm looking to add more low end to my bass rig. I've decided to build an 18" cab that resembles a PA subwoofer, then bi-amp it and set the crossover so that it handles everything below a certain point. I'm not sure where yet, but I think it will be somewhere between 35-70 Hz. Also, I plan to play a bass with a low F# (23 Hz) through it. I need to decide what driver I will be using before I plan the cabinet. What traits should I be looking for in a driver for this application? What would be the the deciding factor(s) of air displacement and how much of that would I need to fill a medium sized club (down to 23 Hz) without PA reinforcement? What makes a driver good (NOT sound quality-wise) for live sound vs home theater or very large venue PAs? Something with the length of the driver's excursion or its rigidity? Or even the surround material, foam vs. rubber? Before I begin to ramble, please share you knowledge with me. I promise I'll make a build thread.