I had a new system put in a Mercedes coupe but it sounds like crap. The fronts were Diamond 600a seperates so I changed them out to Quart Q series but the sound remained about the same. I have the Quarts in another car we own and they sound great so I figured the Diamonds were the problem. In the Mercedes they sound somewhat hollow or flat with little brightness or sizzle in the highs. I've played with the crossovers and headunit EQ but nothing really sounds right. They just sound odd - even the wife can immediately tell something is wrong. The local shop says they don't know what (if anything) is wrong but agree it doesn't sound right. Question is: if some (or any) of the Quart tweeters or mids were wired with reverse polarity, could that cause any of the poor sound I'm describing? They patched into the existing Mercedes wiring in the trunk that runs up to the doors so a mistake could have been made. Is this worth looking into? Anything else it could be? Thanks.
Try reversing them. you can check the polarity by using a 9v battery and some clip-leads. attatch the 9v battery to the speaker wire momentarily. if the polarity is right then the speaker cone will move out. maybe the problem is with the head unit.