i just had a jensen flip-out tv installed (jensen i know, it was a gift!) but the guy that installed hooked the sub up with the driverside back door speaker...doesnt sound too good....how can this be fixed, do i need an amp? the head unit comes with a slot for a sub!! help me cause im an idiot when it comes to this

 

re post this in the audio forum, look at the top of your screen for the "off topic" catagory.. you will see the audio and video section there.

 

sounds like an installer is an amateur, or was too lazy to read the diagram on the factory stereo that vividly displayes the subwoofer wiring.
If you will hook up your stock sub to the unit, it will be very weak. My suggestion either get an amp for the stock SUB, or even better, get a nice amp with a nice aftermarket sub.