if you get a dual 2 ohm, it will need to make the wattage you desire at 1 OR 4 ohms. If you get a dual 4 ohm sub, your amp will need to make the power you desire to put on that sub at 2 ohms. There are two voice coils, when wired together, that produce a final ohm load of either half or double(depending on how you wire it up) the impedance of one of the coils. You need to learn about all of this before you decide on what you want.... it's VERY important that you understand the basics before you spend your money. You can probably learn most of what you will need to know (well enough to not ruin new equipment, anyway) within a week if you study up on it. There's tons of info online.