How to get the best stereo imaging & soundstage
Your car can be a great place to enjoy music
Properly tweaked, your car or truck can be a fantastic place to listen to music. But in order to achieve that level of enjoyment, you need to compensate for some of the vehicle's natural limitations. Achieving great imaging is a matter of understanding your components, and how they interact with your vehicle and the people sitting in it.
With the right gear, you can achieve great stereo imaging in any car, giving your music lifelike dimension across your dash.
Imaging describes the extent to which a stereo system reproduces the timbre and location of the individual instruments accurately and realistically. In a system with superior imaging, you should be able to close your eyes and envision where the instruments were positioned on stage, from right to left. Everyone who really appreciates music in an automotive environment cares about stereo imaging — from the casual enthusiast to the serious competitor.
The speakers themselves should seem to disappear, replaced instead by a spatial arrangement of music sources, or soundstage. Although the front and rear speakers create the soundstage, it should seem to come from in front of you, filling the space from left to center to right.
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 driver 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.
"Side-biased" listening has its disadvantages. The music on your left reaches you before the music on your right. Within certain bandwidths, this imbalance may seem to alter your system's response, emphasizing some frequencies over others. The sounds on your left may also seem louder, distorting the soundstage.
Equalizing path lengths
To get proper imaging, the path lengths between your speakers and your ears need to be as close to equal as possible. These paths should be unobstructed as well. If your left door speaker lies about 2-1/2" feet from your left ear and your right door speaker about five feet from your right ear, you won't hear balanced sound. 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.
You can overcome this problem by installing component speakers mounted in a set of custom kick panels in your car. While this option used to cost a bundle, products like Q-Forms from Q-Logic have made the process easier and more affordable, because they come ready-made for a wide variety of cars and trucks on the road today. With the separates installed in the pods by your feet, you're ensured the equal path lengths vital to good imaging, restoring your music's detail, dynamic balance, and natural soundstage.
You can also overcome unequal path lengths by purchasing an in-dash stereo with digital time correction. Time correction allows you to compensate for speaker placement by adjusting the speed at which the audio signal reaches individual speakers. Using the speaker furthest from your ears as a reference point, you calculate the amount of time that speakers closer to you need to be delayed so that all sounds arrive at your ears at the same time.
Certain brands like Alpine design their car receivers to work with smartphone apps that allow more precise EQ settings.
Other mounting options
Despite the growing popularity of products like Q-Forms and angled tweeters in full-range speakers, many of us still choose to improve our imaging with matched components or by mounting the mid-woofers in factory locations and tweeters up high on the dash or door. You should keep the mid-woofer and tweeter as close together as possible so that the two drivers act together as a single point-source.
While a conventional component speaker set-up does leave path lengths unequal, usually the tweeters have a direct line to your ears, and this lack of obstruction improves the level of detail and the quality of your stereo image. Many matched component sets also let you adjust the firing angle of the tweeters to further optimize imaging. (Keep this feature in mind when shopping for add-on tweeters.)
Adjusting for rear fill
Once you have your front speakers installed to your liking, 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 you should adjust the volume level for rear speakers so that you're barely conscious of their presence.
While your front speakers should give you the best midrange and high frequencies possible, your rear speakers can be conventional coaxials or low frequency drivers. Their purpose is to add ambiance and depth to your forward soundstage. 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.
Setting your subwoofer
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, or that the bass player is dancing her way from your trunk to your front kick panels as she plays higher up the neck. If your amp or in-dash stereo includes a built-in crossover, set the high-pass filters to feed your front speakers the lowest frequencies they can safely handle. Start with your low-pass filter set as low as possible, then raise the crossover point until you hear the "sweet spot", the point at which the bass notes sound clearly defined, punchy, and in front of you. This setup allows some bass to filter from your front speakers and restricts your sub to low bass that 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. 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.