C-Coupe Rear Speakers Sound Terrible

I have the standard non-Bose stereo and the rear seat speakers on my C-Coupe sound terrible. The front speakers by themselves actually sound decent. Is this how it is on other C-Coupes or is there something wrong with my car? What size speaker are these and would changing the speaker make a big difference or does it need a little boost or is the sound limited by physical constraints? Has anyone replaced these speakers or put an amp back there? <br>
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I'm not an audiophile by any means so any help in this area would be appreciated.