I agree with the above comments. In my opinion, it's easier to make a bad subwoofer than anything else. The integration between your main speakers and the sub is a pain. The easy trap to fall into is running the sub too loud, believe I've been there. It sounds awesome at first then it starts to really irritate you. The best setting I found so far is to set the cross over at the lowest possible level and turn up the volume of the sub just enough to notice it.
