Imaging Question

The difference in the distance from your head to the left door midrange and the right door midrange causes the output from the speakers to be out of phase when it reaches your ears. Because this is based on distance, it affects some frequencies and not others. Essentially, door locations put frequencies where the fundamental of most vocals (especially female vocals) occur out of phase. The phase will also be reversed for every multiple of that frequency. It's comb filtering, but the condition that causes what you're hearing is centered at the lowest frequency affected by the difference in distance.

In order to create a phantom center, the speakers have to be in phase. Reversing the polarity of the speakers will put the vocals back in phase, but will put the other information out of phase.

Time alignment fixes this for one seat. A phase-reversing all pass filter can be used to fix the fundamental problem as well, but those aren't included in any car audio processors available in the aftermarket--except for an Infinity Basslink II with the 4sc amplifier module. It includes this filter and has settings for door locations, dash locations and kick panel locations. It also comes with a demo disc that makes choosing the correct switch positions simple. It also makes it possible to demo the filter without installing anything.

Too bad it's discontinued...