Lt. front speaker low volume

[95five-oh]

Hey guys, i have an unusual problem. My left front speaker plays much softer than the other three. When isolating the sound output, the other speakers play as loud on setting 7 as the lt. front plays on setting 15. I've switched it with the pass. side speaker and the result is the same, so the speaker is good. The immediate wiring seems fine with no visible splices. The head unit is an alpine 9856....both the speakers and HU are only ~2-3 years old and barely used as this isn't my DD. Any ideas here? TIA

 

[HISSIN50]

I'd connect a speaker to the Left-front speaker inputs at the HU itself (to remove the body wiring from the equation). If the output is normal, the speaker wiring probably broke in the articulated boot in the driver door. The wires get flexed, and the driver door gets way more use than the passenger door, so those wires break first.

If that's the issue, I'd just run new wires. Or at least install a solid (soldered) splice from the kick panel, though the boot and to the speaker.