The voice coils will determine the final ohm load you can wire it up to the amp at. When running off the amp, 1 ohm is going to be the least efficient and 4 ohm will be the most efficient. Of course 2 ohm would be somewhere in the middle. Efficiency means how much current the amp is drawing off your car in order to produce the power its creating. For example, if you have a 500 rms amp and say it's 80% efficient, 500/0.80= 625. So your electrical would be seeing 625 watts, while your amp would be producing 500. This is important so you don't pull more current than your alt and battery can handle. It'll also be important to upgrade your big 3 and be sure to have a solid ground in the rear for your amp. Most amps are rated at 14.4 input voltage and as the voltage drops, so will the output from your amp. Maintaining your voltage as high as possible helps with your overall output from the amp. Different ohm loads as determine dampening over the sub, this is important for sound quality. Some people will say you won't be able to hear the difference from 1 ohm or 4 ohm, but 4 ohm will offer greater dampening than 1 ohm will. Dampening is basically control over the woofer. When the tone the sub is playing stops, how quickly does the woofer respond. A single voice coil will do as stated, a dual voice coil, by itself will go up or down from its stated ohm load. A dual 2 ohm can be wire 4 ohm or 1 ohm and a dual 4 ohm can be wire to 8 ohm or 2 ohm.