bril814

Some day, one of the 4 speakers (front driver, front passenger, rear driver, rear passenger) make sound midrange and treble only, no bass.

After for a while, the rest of 3 speakers don't sound bass anymore in order.

Now my A4 car audio don't make bass sound at all.

With the help from Youtube, I removed the interior door panel and checked up the speakers with the electric tester.
As a result, I assume that the speakers works and audio unit doesn't work well.

Is there anyone who has the same problem?
Somebody who advise me what to do to solve this kind of malfunction?