I once knew a guy who put a 10 inch sub in the floor board behind the drivers seat. No box or anything just sitting in the floor and he just spliced off one of the rear speakers. Any ways this thread made me think of that. Yes you HAVE to have an amp if you want a sub to sound like it is supposed to. If you want to get more bass with out adding an amp then you need to replace the speakers that came in the car, and even then it is a good idea to get an amp. but if you just hook up a sub by splicing the wires going to one of the speakers will probadly not even be able to tell that it is there. the factory system DOES NOT have the power to push a sub.