While humongous-sounding bass may let people know you're coming, true car audiophiles know that what really keeps people listening to a system is more than a matter of volume and unbelievable bottom end.

Overall sound quality, how naturally a car stereo recreates the sound of a master recording, is a key concern of everyone who really appreciates music in an automotive environment ¡ª from the casual enthusiast to the serious competitor. And a big part of the overall sonic impression your system makes has to do with the quality of your stereo image.

When we use the words image or imaging , we're talking about a speaker system's ability to create sound in such a way that you can close your eyes and envision where all the musicians were standing when the recording was made. The position of the voices and instruments should be easily identifiable and shouldn't seem to change with frequency variation.

The speakers themselves should seem to disappear, replaced instead by this spatial arrangement of music sources, or soundstage . Although the soundstage is created by both front and rear speakers, it should seem to come from in front of you, filling the space from left to center to right.

Getting great imaging is a matter of understanding not only your components themselves, but also how they interact with your vehicle and the people sitting in it. Properly tweaked, your car or truck can be a dynamic "listening capsule" ¡ª a fantastic place to listen to music. But in order to get your vehicle to provide that type of environment, you need to compensate for some of its natural limitations.

"Side-biased" listening
When you listen to tunes at home, you probably don't make a habit of planting yourself smack dab in front of your left speaker. If you did, you'd be missing out on the detail the right channel has to offer, as well as the spaciousness of a complete stereo image. Yet when you listen to music in the driver's seat of your car, and you have conventional speakers in your doors or dash, you probably get the same type of imbalanced listening experience.

To get proper imaging, you need as close as possible to equal path lengths between your speakers and your ears. These paths should be unobstructed as well. With your left door speaker about 2-1/2" feet from your left ear and your right door speaker about five feet from your right ear, this is clearly not the case. Playing with the receiver's balance control can help the driver's listening experience, but it throws the image out of whack for the person in the passenger seat.

There are a number of disadvantages to this "side-biased" listening. The music on your left reaches you before the music on your right. Within certain bandwidths, this may seem to alter your system's response, emphasizing some frequencies over others. The sounds on your left may also seem louder, which will distort the soundstage.

Other mounting options
Despite the growing popularity of products like Q-Forms, many of us, for reasons of taste or budget, still choose to improve our imaging with a more traditional use of matched components, mounting the mid-woofers in factory locations and tweeters up high on the dash or door. It's wise to keep the mid-woofer and tweeter as close together as possible so that the two drivers will act together as a single point source.

While a conventional component speaker set-up does leave path lengths unequal, there usually is a direct line from the tweeters to your ears, and this lack of obstruction alone really steps up the level of detail and the quality of your stereo image. Many matched component sets let you adjust the firing angle of the tweeters to further optimize imaging. (Keep this feature in mind when shopping for add-on tweeters.) In fact, a number of forward thinking speaker manufacturers now offer this feature on several of their coaxial speakers.

Adjusting for rear fill
Once you have your front speakers set up the way you want them, you'll want to make sure that your rear speakers are doing their part to create an ideal soundstage. While personal taste plays a role here, most experts agree that the correct volume for rear speakers is where you're just barely conscious of their presence.

While your front speakers should give you the best high frequencies possible, your rear speakers can be conventional coaxials or low frequency drivers. Their purpose is to add ambience and depth to your forward soundstage and if they reveal too much high frequency information, they'll "pull" the stereo image to the rear of your vehicle, away from where you want it.

If you're running a subwoofer in your trunk, you want to avoid the sensation that all the bass is coming from the rear of the car. To keep the soundstage up front, set your crossover to feed your front speakers the lowest frequencies they can safely handle and set your subwoofer crossover between 80 and 100 Hz if your system allows. This setup allows some bass to come from your front speakers and restricts your sub to low bass which is very difficult to localize.

Testing your system
When you have all your components in place, test your system to see that it's imaging properly. We recommend using the material on. The discs in this series provide several tracks to evaluate your system's imaging and to help you determine exactly where corrections are needed. They also provide a broad group of tests along with several music tracks that are great for overall system appraisal.

As you tweak your system to perfection, spend some time listening to other people's set-ups, informally or at sound-off competitions. Rather than attempting to precisely duplicate the systems you like, try to pick up general concepts and techniques, keeping in mind that every vehicle differs acoustically. What sounds great in a trophy-winning Camaro may muddy up the sound of your BMW. Besides, some of us like very precise imaging, while others among us prefer sound that is a little more spacious and open.

In the final analysis the stereo image that suits your tastes is the one that's right for you. So, trust your ears.