What is the fix for my car speaker?
Try swapping the left and right front speakers. You might find out that the left channel of your stereo is weak. Or you might need to swap the + and - wires on that speaker.
Did you have this problem before installing your new speakers or did you notice it after installing them? It may just be a faulty speaker if all your other speakers are performing like they should. A good way to see if your head unit is causing the problem is to swap speakers with the other ones and see if the problem is still the same or if it changes because 1) If the problems still persists (even after swapping speakers) where your driverside front speaker is still not getting as low as your other speakers, it probably means that your head unit either needs to be replaced or the wiring may not be secured or 2) if you swap your speakers and the problem follows wherever your speaker is being moved to means that you may just need to get a new speaker.
Stereo isn't equal program left to right, but examine your connections again. Make sure your left front speaker is connected to left front wires and not grounded in any way. You could also swap speakers left to right to see if that one speaker itself is faulty. Maybe its bass element doesn't work. Good luck.
When something is out of your league, you see the professionals. Time to see a very good car audio shop.