Have you ever seen stock car speakers facing outwards from under the seat? Although stock speakers in cars are no engineering marvels, they aren't engineering failures. Or, think about it this way: If you were at a concert, you wouldn't have your back to the stage, correct? Thats what your doing by putting speakers (not subwoofers) behind you. If you have a proper front stage (the speakers in the front of your car), ie. a component set (a midbass speaker, usually ranging in size from 5.25" to 6.5", in normal applications, and a tweeter, both of which use a passive crossover that is provided with the component set), that is powered by an amplifier, with, at a minimum, your door sound-deadened, your front stage will be plenty loud enough to keep up with most any subwoofer application. Rear fill (the speakers in the backseat of your vehicle) are usually unnecessary, but alot of people like to throw them back there anyways.
