I have a 2004 e46 BMW 330ci convertible and i want a aftermarket sub that i can replace with my stock harmon and kardon sub that will fit right without any cutting and i don't want a box either. My sub is in the middle of the 2 seats in the back.
Your not going to get anything GREAT
beacuse thatg subwoofer is a free air subs therefore it doesnt use a box to stop the cone and produce bass, meaning that it cannot be THAT powerful.
To even suggest a subwoofer you need to put the specifications of its fit.