Choosing a subwoofer is not only about size, RMS power, or how much bass you want. One specification that can change the entire setup is impedance. When shopping for a new subwoofer, you will often see 2-ohm and 4-ohm models sitting next to each other, and it is easy to assume one must simply be better. The reality is different. A 2-ohm subwoofer can allow an amplifier to deliver more power...