The bass from my sound system suddenly disappeared. Its not a blown sub!
 

The bass out of the OEM alpine system has suddenly been reduced dramatically. It just happened out of nowhere. The sub has been blown for 4 years now, so nothing has changed in regards to that. The bass from the door speakers is not very deep and sounds weak, even when the bass is turned all the way up. I have played around with the seating position adjustment, bass,treble, and sub settings to no avail. Disconnecting the battery made no difference. Overall the sound system sounds like how I would suspect the standard system to sound like. Even passengers have noticed that it doesn't sound as "high end" anymore.

Thoughts?