A Crossover is not a Puzzle. Well, sort of.
You can severely damage your speakers if you don’t pay attention to the way your amps and crossovers work together. For example, if you’re forcing too much high volume bass out of a smaller midrange or tweeter speaker, you’re going to force the speaker to its “excursion limit,” or its limit of movement. The voice coil in the stressed out speaker bangs around, gets bent out of shape, and destroys your speaker (see the page on how a speaker works for more about speaker movement).
Not surprisingly, this is a common problem with 4" and smaller full-range and coaxial speakers. And equally unsurprising, there’s an easy way to prevent it. Simply “roll off” speakers with an in-line capacitor-or “bass blocker”-to keep the lowest bass frequencies from getting to that driver. (You won’t be “missing” anything, since you’ll be filtering out frequencies the speaker can’t reproduce anyway, and your subwoofer will easily pick up the slack.) Any good car stereo dealer can help you choose a capacitor value that’s right for your speakers. They probably have them in stock, too.
There are Two Types of Crossovers: Active and Passive.
A passive crossover appears in the circuit after your amplifiers, and divides the signal that then goes to your speakers. A passive crossover has no power, ground, or turn-on leads and are rather inexpensive. But, they tend to be inefficient and can even add some distortion.
An active, or electronic, crossover does its job before the amp, taking the signal directly from your head unit before it gets to the amplifier and needs an external power source. Active crossovers give you control over which frequencies you want to use as the crossover points for bass and treble. Some active crossovers allow you to customize the crossover slope as well as the crossover point. Because they filter frequencies before the signal is amplified, active crossovers ensure that the amp gives its full attention to the filtered signal, which is very efficient.
Chose your crossover points and crossover slopes by consulting the frequency response measurement on your speaker specs. The frequency response is the range of frequencies that the speaker can successfully reproduce. The frequency response of two separate speakers (woofer and midrange, for example) must overlap a little, or you will hear a “gap” in the music. The crossover point appears within this overlap. The crossover slope is a measurement of how abruptly the crossover cuts off the speaker’s sound beyond that crossover point. If your speaker frequencies overlap just a little, use a steeper slope. The steeper the slope the narrower the range within which two speakers are producing the same signal, and the smoother the transition from one speaker to the next. The opposite is also generally true.
This article was last modified Dec 8, 2013