Every car interior is different. There are different shapes and materials inside and as the sound bounces off the interior walls it changes the acoustics and sound. If you are going to install the perfect sound system and truly looking for perfection you must take all this into consideration and that means doing a complete Interior Automotive Acoustic Analysis and Study. Only then can you achieve Perfection in Car Audio Sound.
There is a lot of math involved in perfection of sound waves and a good cad cam technician and PhD researcher in sound waves can help you get there. Additionally you must understand simply putting the speakers, tweeters, base and treble where ever they fit makes no sense at all if you are into perfection. You see as the sound moves through the car it hits the walls and bounces off again. Some of that sound you will want to bounce in certain directions so each passenger in each seat gets the full impact.
While other sounds you want to then dissipate and this is where the special materials can be used in the seat fibers or headliners. Even special coatings on the glass can