Let me reprase that. The knob should be the reason it is doing it. You would get the same results if you turned up your gain while its off (prolly havent done that huh?). How did you setup up your gains using the bass knob?
I had a buddy that did a 150 in a van with a single l7 with 1500 watts, so dont say they wont get loud.
They can handle more then 1000 but its not recommended. The most i would put to it is 1500.