staging is a very tough one to get 'right' and its taken me a couple of years to get close to what i think sounds natural, big, wide and balanced.
i wont try and give you a fixed formula or any dogma - or i will say is, experiment with different components, locations, alignements (aiming) and above all else CHEAT
a car is not a purist environment, so its ok to go against the rules of stereo to restore what the car takes out.
as a 'to-get-u-started' consider angled pods (doors or kicks) low and forward, each pod aimed at the opposite listener, trying keeping mid and tweet together, and then try other stuff to improve from there. this is the standard formula, and while it is limited in what it can do i find it gives the basic ingredients for great sound.
as for centre channels - i am one of the few people i know who use one. i used to curse even the idea of a centre channel - until i tried it
it isnt necessary for serious SQ, its just another way to 'cheat' and get around the fact that your sitting outside the magic-V. i personally love what it has done for my system, the stage is very balanced from left to right, the stage is actually 'detached' from the speakers, and obtaining that ever elusive centre image is now a real possibility. however, to make it work well, i find that you MUST equalise the centre independently of the left/right array. while my basic tuning is done, im still doing the fine tuning but so far im very impressed.
as a side note, experiments in Barme's car which i am helping to build has shown digital time alignment to provide good results in evening out image placement and providing a discernable centre image - so thats another way to cheat
but that doesn't affect the stage.
another thing the Americans are doing (and that im now doing also) is to add ambient satellite speakers higher up in the car to raise the sound stage and provide added ambience - can also help counteract the 'rainbow' effect. while you should still have the tweets next to the mids, having secondary ones higher up and set/EQ'ed properly can provide some trickery for improving height (and also depth i've found).
in short - get some cheap mids and tweets, hook them up to looooong speaker leads from your amp, and start bluetac'ing em in different places and take notes. this will help to find what will get your car staging well. what you generally look/listen for is a stage that is wide (same as car cabin width), about as high as the upper dash/bonnet, and has depth and dimension.
imaging (location/definition of instruments and vocalists etc) is then another problem
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Custom SQ System
Source: Clarion DRX-9675z - Front Stage: Boston Acoustics Pro 6.5's - Centre Channel: Boston Acoustics FS50 Midrange - Ambient Satellites: Boston Acoustics 3/4" Kortec Tweeters - Processors: Audiocontrol EQT's - Subwoofers: Earthquake BR12's - Amplifiers: Kicker IX404's - Power: Stinger 1 Farad HPM CapacitorSounding sweet and taking it to the street
