Originally Posted by Skauber

Depends on the amp, if the amp is rated 2 ohm stable and you bridge it, then it needs minimum 4 ohms in bridge mode. 2 vs 4 ohms isn't really that important when talking 2-300w subs. 300w in 2 or 4 ohms sounds the same, the only difference is the amp. That Pioneer mentioned above doesn't require anything major to drive it, and if you go with that amp I linked you'd have to bridge the amp and wire it to 4 ohms. When you're diving into large systems, then it gets more important to go with lower impedance, even down to 0.5 ohms in huge systems.