We're back...
In the last "Tweak and Tune" article (Oct. '07), we covered some theory and techniques on the basics of setting the crossovers in your system. In this article, we're going to take the next step and get into some practical application of the theory and techniques.
We'll look at active and passive crossovers, and the techniques involved when using only our ears and some familiar recordings to make adjustments. We'll also discuss using an RTA to help tweak the crossovers, followed by using our ears for final system tweaking.
Before getting too far ahead of the game, make sure to read the previous article (if you haven't already) and review it if you already have. Next, make absolutely sure you're familiar with all the features of the system components you'll be using. You should know what all of the controls on the amplifiers, head unit, passive crossovers and on any other components do before attempting to perform any serious system tuning. All too often (and believe me I've done it myself), we jump right in and try to figure it out as we go. Sometimes we're successful, but often, we spend a lot more time "figuring it out" when it would have been much quicker and easier to read the manual first.
R.T.F.M... Read The Factory Manual
Once you acquire a lot of experience, it's easier to take some shortcuts. But even if you're totally familiar with the components and the type of system being tweaked, it's a good idea to follow a standard procedure. The results will be much more consistent and you'll work faster too.
Tuning a Basic System Using Basic Techniques
Let's look at a relatively simple system using a basic head unit, a 2-channel amplifier connected to passive crossovers for the midrange/tweeter speakers and a single-channel low-frequency amp with a subwoofer. After ensuring all connections are made correctly as recommended in the manuals, we need to make some initial crossover settings before turning the system on.
With passive crossovers, set any switches or jumper terminals to the reference or neutral position. We'll try the different positions for these later, but for now, we need a starting reference. On the amplifiers, set the gain control all the way down and neutralize any bass contouring or equalization controls.
On a basic system like this one, the only crossover settings you'll need to work with will be between the subwoofer and midrange frequencies. This active crossover can be inside the head unit with dedicated subwoofer and high-frequency signal output channels. Or, it may be crossovers as part of the input stage of one or both of the amplifiers. The specifics depend entirely on the components you have in the system, so it's impossible to give very precise details here. Wherever the crossover controls are, try setting the lowpass crossover for the subwoofer and the highpass crossover for the midrange/tweeter amp somewhere between 70 and 90Hz. If the crossover slopes can be adjusted, set both the low- and highpass slopes to the same setting, probably 12 or 24dB per octave. Again, these are just starting points.
Now, it's time to set the system gain structure for all the components. Setting the gain structure is a very critical step, but I'd bet over 90 percent of all aftermarket car audio systems built don't have the system gain structure optimized. Setting crossovers and gain structure go hand-in-hand. One definitely can affect the other. When gain structure is set properly, the system will achieve maximum output levels with minimum noise and distortion, the system will be reliable and you will have total usability of all controls, including the ability to turn the volume control all the way up without fear of blowing something apart. It's not that difficult to do and it doesn't take much time, but it does require some special techniques and a couple of special tools. Unfortunately, it will require another article to fully explain gain setting (probably in the next "Tweak and Tune").