Installation Question

Correcting phaseing problems inside a car is very difficult.  You have to add DSP time-domain alignment circuits (time delays) to adjust the relative timing between the various drivers.  This is very time consuming and requires significant electrical engineering ability to design yourself.  You are in Bob Carver's field of psycoacoustics now.  An even bigger problem in a system like you describe will be phase problems cause by reflections and cabin gain, rather than those caused by the actual timing from one driver to another.  As wattage increases, the acoustic cancellations from reflections inside a small enclosed space become a bigger and bigger problem, especially if you are using long-throw drivers.  Near-field monitor designs have fewer such problems, but then you wouldn't push those with 4K watts, nor would you use them in a car... 

The best thing you could probably do is install some good quality DSP processors with either Dolby AC-3 or THX parameter compliant capability (like those with a Motorola DSP-560001 chip) and use them to digitally adjust your time alignments, rather than try to design and build something yourself.  I could suggest some equipment for home or theatre audio, but I'm not familiar with available car audio equivalents.  Look for DSP gadgets!

PHASE LAG

   Phase Lag is a term first expained by a Tech that worked for Rockford Fosgate in the mid 80s.

On speaker systems where the woofer and midrange speakers are separated by more than a couple of feet, the travel time of sound through air can produce what is called a PHASE LAG  leading to cancellation .  For the reason On any installation (even with other than 12 db crossovers) try reversing both woofer phases. In almost all cases bass will be mush tighter with woofer reversed.

When a high and low-pass pair of 12 db/octave filters are used, Cancellation  can be avoided by one simple step:

Reverse the woofer phase by reversing the wiring to the + and - terminals. Reversing the woofers has the effect of putting the woofer and midrange back in phase at the crossover frequency, to compaensate for the crossover's phase reversal. Some high end Amplifiers use this feature a 12 db/octave active crossovers, and are wired to use this reversal technique.

These considerations also apply to midrange-to-tweeter crossovers, although usually the problems introduced are less audible. The cure is the same, but applied to the tweeter. Reverse the tweeter phase by reversing the + and - terminale

In General , the acoustics of Auto and the variations of speaker placement can produse a variety of unexpected cancellations. Where possible, experiment with speaker phasing by comparing the sound of the system with in-phase and reversed woofers and /or tweeters to find the smoothest sounding connections.

Avoid Cancellation

Thank You

Julian59