Why does my subwoofer sound distorted?

im not really handy when it comes to car audio. Never really tried to install anything myself. a while back my ex-gf's father hooked up a system in my car. wasnt much. like 700 watt amp pushing two 12 inch subs. just enough to give me a thump but not shake the block. anyway, i had to unplug the entire thing to... show more im not really handy when it comes to car audio. Never really tried to install anything myself. a while back my ex-gf's father hooked up a system in my car. wasnt much. like 700 watt amp pushing two 12 inch subs. just enough to give me a thump but not shake the block. anyway, i had to unplug the entire thing to get to my spare tire, which was under the sub box in the trunk of my car. when i did that, two things happened. my battery died and the fuse in the cord running from the battery to the amp shattered (it was made of glass). so after several weeks i decide to put everything back together myself. was pretty simple since everything was already installed. just had to plug things back up and buy a new fuse. now, it sounds ok when one of the subs is plugged to the amp, but when i plug both up it seems like they lose power and sound slightly distorted. i no longer have that crisp bass anymore. so im wondering could i have blown out the system or could the fuse be the wrong size?
Update: thanx for all the help guys. turns out it was the polarity issue. the speakers were out of phase. i switched the wires around and it sounds brand new. thanx again!! i love you all haha
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