ChickenWinGs

Hey guys.. i just purchased a RE SXX12D2 and a hifonics brz1200.d with a 4 gauge Rockford fosgate amp kit and im getting my custom box made for the sub. i wanted to know how it would sound it my car? its a mitsubishi eclipse.. i called a few websites and they suggested a 10'' or 12'' max they said a 15 would be too much for the car, and i also wanted to know will my stock alternator with an upgraded battery and big 3 will be able efficent enough to power the system? thanks!