Sound not coming from all speakers

[anm]

Hi,
My octavia has factory fitted music system. Sound does not come from the woofers at the back. What could be the issue?
The receiver is 4 channel only so I guess it can power the 2 tweeters and 2 speakers in front doors. Could it mean that rear speakers are not at all wired?
If I try to get other speakers connected to the same receiver, could it blow up the system? Should I buy exta amp to power remaining speakers?

regards

[carparts.abhi1]

You can install a bass tube.

[TDI 100]

THE DOOR TWEETERS RUN OF THE SAME SAPPLY AS THE DOOR speakers. Sounds more like a fault with the head unit rear speaker outputs and replacement is the only real thing. but test the ouput when removing radio if there is signal at head unit end some new wires will be required

[TDI 100]

Have you tried adjusting the balence/fade controls

[bigbrother]

Just got a level 1 Fabia that has 4 speakers - trouble is they are all in the front (2 x doors and 2 x "A" pillars). I noticed the level 2 spec has 6 speakers so i guess they are the additional rears that i kind of expected.
Regards,
bb