Imaging And Staging
Imaging is being able to pick certain sounds from certain places. The singer would normally be located towards the middle of the car, in a car audio installation, guitars, trumpets, and other instruments towards the sides of the car, in a car audio installation. If you scatter speakers all around the car, in a car audio installation, your imaging would be very poor, since you would be producing the same sound at different places. If you have a system with good imaging, the sound should seem to come from different instruments and voices, not speakers.
Staging is the ability of a system to "fool you" into thinking that everything (including bass) is in front of you. The sound should be similar to a stage in a concert, where the singer would be in the front center, and the rest of the instruments and background vocalists would be located to the left and right (but always on the front). Good staging and imaging are not so easy to implement in a car audio installation. It takes a lot experimenting with speaker location and direction.
Directivity of sound is related to frequency. At higher frequencies it is easier to pinpoint where the sound is coming from, than lower frequencies. This can be used to our advantage in car audio installation. Tweeters are the most important part of getting good staging. They should be aimed towards the middle of the car, in a car audio installation. A way to "bring" the bass to the front of the car is to fool our ears by overlapping frequencies played by midbass and subs, so that your midbass actually "pull" the bass to the front, since lower bass in not too directional. You should crossover your midbass as low as you can (without getting distortion). Then cut your subs at a bit higher frequency. This will mix the bass coming from the front and rear, making the bass seem to come from the front. Adding a center channel also improves staging, if it is set up correctly, in your car audio installation.