Need help with door speaker resonance, aftermarket speakers 2001 A6

[ENDEE666]

Installed all new speakers a while back in my 2001 A6. CDT Components, amplified & xover'd. Along with a sub & JL Audio Cleansweep. They sound really good with one exception. One of the doors is getting some bad mid bass resonance & muddy sound. Both front speakers are the same, and both doors are the same, yet one speakers sounds bad.. I thought it was maybe a damping issue, so I added a couple layers of dynamat to the inside of the door skin & a bunch of other areas. It did not help at all... But why would that matter on one door and not the others? So now what should I do to fix this? The muddy sound is killing all of it...

[b6onboost]

Make sure the wiring is solid. Make sure the amp gains and cross overs are set equally. Then on the amp where it powers the front speakers, flip them. So the channel that was powering right now powers left and vice versa. If the same physical speaker still sounds muddy its likely faulty. If the muddy sound switches sides...then the amp channel or rca input to that channel is bad. To determine if its the rca input or amp channel...switch the rca input providing signal to the muddy channel. If it sounds clear then the rca/signal is bad. If it doesn't change then the specific amp channel is bad.

This will help isolate the problem.