If you tried to set it for 1200 watts, its safe to say you are clipping the sub. From my own prior experience (and yes i have a damn o-scope) you will start to see a dirty pattern around 1050 watts depending on your input signal and voltage drop. If you have no idea where your head unit starts to throw out a clipped signal, if it does, then you could be clipping a lot worse than you think.
Find someone with an o-scope, set it up correctly, and save your equipment and your wallet some money. You will thank yourself later...