Speaker location determines your entire sound image. The problem with cars is that fact that the listener isn't in the middle of two speakers but in a corner making one speaker sound louder than the other. The distance between the left speaker and the left ear isn't the same as the distance between the right speaker and right ear. Try to make the difference between the distance on the left and right as little as possible. Placing the speakers near the ground does the job but creates a risk of sound coming from below. Placing an extra speaker on the dashboard doesn't help because that will rip the sound in two.

To find the perfect location in your car temporarily install the front speakers in card board boxes. This test is only to find a location, so poor sound due to the minimal enclosure of the card board boxes is no problem. Play at a low volume, the speakers may even be driven by a home audio system, and move the speakers around the car to find the perfect location. Listen, don't look. Some very unlikely places may proof to be good for audio.

Subwoofer location cannot be found using this method. Location of amplifiers and other equipment is a cosmetical case only. Just keep in mind that some devices may interfere with each other.