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Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 21614
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Just bought a 2011 Mercedes C250 Estate CDI. The sound system

Resolved Question:

Just bought a 2011 Mercedes C250 Estate CDI. The sound system is thinner and more mid dominant at speed, so I've run phase tests on the speakers and found bad phasing.
How easy is it to reverse the phasing as a DIY job?
Submitted: 1 year ago.
Category: Mercedes
Expert:  Matt replied 1 year ago.
Hello the usual method is to hook up your front speakers properly phased (i.e., receiver+ to speaker+ and receiver- to speaker-).and then hook up these rear speakers as follows: receiver+ to speaker+ but speaker- to speaker-. In other words the left and right rear speakers have their + going to the L and R receiver+ but they're - going to each other now to achieve this in car will mean removing the rear door trim cards, the 'b' pillar trim and lifting the carpet and also getting into the boot if you have the optional rear parcel shelf speakers so its not difficult just a bit long winded, as wires will need running across the car, through the b pillar and through the rubber boot that crosses over the door hinge line so be prepared to take a lot of trim panels out achieve what you want
Customer: replied 1 year ago.
REARS: Do you mean the rears mono up? And how do I remove the rear door panels? Just the screws under the arm rests?FRONTS: Door panel removal, again, just the screws under the arm rests?RECEIVER: How do I access the receiver wiring to check the colours for +ve and -ve?
Expert:  Matt replied 1 year ago.
the +ve & -ve terminals are marked on the back of the speakers so there's no need to remove the receiver / head unit
and yes to remove the door panels there's a couple of screws tucked away under the arm rest and sometimes in the corners under speaker trim and the door bin
then it pulls away off its clips take it slow and use a large flat bladed tool to prise the panel off
Customer: replied 1 year ago.
ok thanks - but if I have phase problems, surely I need to check the wiring at the back of the radio? I mean all it takes is one wire wrong at the back of the stereo
Expert:  Matt replied 1 year ago.
Hello I agree that would be wise as its possible that the issue may be the original wiring is not correct on the head unit
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