I wasntld on underground subs for the longest time. I bought a 12" fi btl and a hifonics amp off a kid on Craigslist. It beat really hard in his Dakota in the back seat in a box built for the sub tuned to 30 something hertz. I went home hooked it up in the back of my trailblazer, same wiring, didn't touch the sub kept it at 1 ohm, and it barely sounded like I had a system, I figured it was cuz I had a bigger cabin area, I was pissed and sold the sub for 150, kept the amp and put 3 cvr's on it. Much better, like 2 weeks later i sold the cvrs and threw 3 cvx's on the amp in the same 3 cube sealed box and i was happy for a while. Then i had a fire in my car when a speaker terminal melted, and someone broke into my house a month later and stole my subs. So i went all winter without bumps, first break of nice wether i went and bought the first 2 l7's on a limited budget