Sound suystem

hello there , i have just got a 2001 golf 1.4s, loving it so far, but im only get sond out of the drivers side door, theres no sound from the back doors either , whys this.i have fully check adjusted the balance, to the left and ionly get sound form the tweeter, in the passenger side door.

how are the back doors wired in, are there to the front door speakers as my car radio doesnt seem to have an output for the rear, is this common on 5 door golf ?S

Thanks