2006 civic Ex
110k
has a back bass amp but standard factory install stereo
front speaker are LOW volume I can hear sound, barely but very low.
Back speaker are fine. I turned gain and cut over all the way down on the Bass Amp in the rear

Just recently, the right front passenger came on. Still low on left front driver. Rears seem fine.
This is my kids car (ie she's had it for 3 years from 16-19). She loves it LOUD. Apple doesn't fall far from the tree...LOL. I thought she might have blown out the front Amp chip.
One solution I as thinking was to just replace the factory stereo---they are like $150 on ebay.
Thoughts

 

Check if the terminals are corroded on the speakers.