I read in an article the best way to improve audio is to upgrade the
speakers. Car is 1992 190E 2.6,  that seems to have had a factory phone
set up, because the  drivers side dash speaker, aside from the normal
bullet connecter,(green and black wires) also had double A battery,
sized condenser attached to it with a plastic strap that plugged into
two wires (blue and brown) via 2 pronged factory plug .     I installed
two Kenwood 51/4 speakers in the rear and two Kenwood 4" in front  using
soldered on bullit connecters from old speakers.    Both rear speakers
went dead in two days,   passenger side speaker output is 30% less than
drivers side,.. sometimes less.    Rehecking every thing I find ....OEM
speakers are 6 ohm, Kenwoods are 4 ohm,  4" and 51/4"...Both door
speakers  work, ... (by running wires from dash speaker wires  to door
speaker contacts.     Alpine amplifier in trunk  not working properly
(door speakers never made a sound)    Dealer: "never heard of one going
bad", "Two hours labor to check it out"    What killed the rear
speakers?   Is that condenser vital to this system ?      Dealer; "what
condenser?.....Got a special telephone speaker in the book, costs 170.oo
........can anyone help untangle this