guys.. my car stock sony 9 speaker audio is great however i feel the speakers on my doors bass sometimes goes overboard and it makes unpleasant bass rattles. so i'm thinking of reducing bass on the door speakers and channel the bass to my boot. so adding a subwoofer is the way. but i want to find out if i can add like a powered sub or something like that on top of my existing system and if that would be effective? I do not want to add extra amps if that is possible. doable??? opinions and suggestions welcomed. thanks.