jumpman is correct, but that (ohms law) affects the amplifiers output substantially in that the lower the impedance(ohms)=higher the wattage output from the amp. that's because, like jumpman said, it's about resistance, lower ohms = less resistance. Also, it's Very important to know how to wire a DVC woofer on either a mono amp or bridged, you can either cut your power by 50% or effectively double it right there. Just be sure if you buy a dual voice coil sub with 2ohm voice coils, that your amp can handle a 1 ohm load, which is pushin wattage under any circumstances.