is an amp required?

I've heard of people hooking up subs without using an amp. I didn't think that was possible or a good idea but if anybody knows how to do that please tell me how to do it.

Well hooking up subs without an amp would be a waste of money on the subs. Subs will not play properly without lots of power no head unit can supply this kind of power. It also is no good for subs to be underpowerd which is what would happen. They will not sound clean, they will be distorted, they will not have the bass you are looking for. What kind of subs are you planning on using?? What kind of head unit do you have?? What kind of box design are you gonna use? Some of pionner head units clame that you can bridge the rear channels to supply 50 watts rms to a sub ,I have yet to try this and I probably won't. I would use an amp that that particualar sub needs ,post back with some more info and we can help a lot more.