car stereo systems run of 2 to 4 ohm impedance. home theater systems run on 8 ohms. if you connect a 4 ohm speaker to a 8 ohm home stereo you will overheat the amp and burn it out. to fix this problem, hook your two 4 ohm 12" subs in series mode. to do this, connect the positive on sub #1 to positive output on the amp. take the negative on sub #1 to the positive on sub #2, then connect the negative on sub #2 to the negative on the amp. by doing this, you have converted your two 4 ohm subwoofer speakers into one 8 ohm load which the home stereo amplifier can handle.