Ok here's my setup; I have 2 12" Alpine Type X subs in an Alpine ported enclosure; 2 PDX-M12 and 1 PDX-F6; I have a 5 farad cap and a fused distribution block and Kenwood Excelon HU. The problem I am having is I pulled the stereo out of my old car and set it up in my new car when I play songs the subs don't hit hard they sound weak and like they are in a sealed box; if I unplug either one of the amps RCAs the sub hits hard. But as soon as I have them both plugged in with RCAs weak sounding again.