no base in my a4 cab

[zia]

i drive a 04 plate a4 cab,the front 2 door+back 2 door base speakers are not working,its a symphony 11 head unit,i would like to no if they are wired to the head unit or a seperate amp+were is the amp in the car if they are wired to it.thanks for your help.zia

 

[AndyMac]

If it's non Bose then the fronts run off the HU and the rears off a seperate amp. If it's Bose then they all run off a seperate amp.
So all you're getting is the tweeters?
Has this just happened, or has it always been like this?
Very strange that all 4 woofers would suddenly stop working. If the tweeters are working then it can't be wiring related as they run off the same wiring as the woofers.