JL Audio C5-570 component speaker system: woofers, tweeters, and crossovers

What can a crossover do for you?

A crossover is any device that limits the range of frequencies sent to a speaker. Think of a crossover network as an audio traffic cop, directing highs to your tweeters, midrange to your midwoofers and low bass to your subwoofer.

Without a crossover, a messy, sonic "traffic jam" results. Your midrange and subwoofer duplicate too many of the same frequencies and your sub wastes time trying to put out high notes it wasn't meant to handle. A "fatal pile-up" could also occur, with your tweets being destroyed by some renegade tractor-trailer of a bass note thumping along in the wrong audio lane.

Because they're essential, you'll find crossovers in some form almost any time speakers are present. If your home stereo uses a pair of 2-way bookshelf speakers, it uses a 2-way crossover. Within this crossover, a high-pass filter blocks lows and passes highs to the tweeter while a low-pass filter blocks highs and passes lows to the woofer.

What to look for:

There are basically three kinds of crossovers: active, passive, and in-line.

• A passive crossover installs easily next to your speaker system and doesn't need to be hooked up to a power source. All crossovers electronically filter signals so that speakers, or amplifiers, get only the range of frequencies — high, mid, or low — they're designed to reproduce. For instance, a full-range signal exits an amplifier and goes to a passive crossover which separates the signal into two parts and sends the high notes to a tweeter and the mid and low notes to a woofer.

F-MODS 100 Hz low-pass in-line crossovers

• Besides passive crossovers that operate on speaker-level signals and connect between your amp and your speaker components, there are also in-line crossovers that connect before the amplifier. In-line crossovers make sure your amplifiers don't waste energy amplifying signals you don't want — like the high frequency notes in the full-range signals your receiver sends to your subwoofer amp that would be filtered out later anyway.

  Installing an in-line crossover is a great and inexpensive way to sharpen the sounds of your system, especially in a component speaker system. In-line crossovers each come set to a specific frequency and can't be adjusted. Fine-tuning is accomplished by using the crossover built into almost every car amplifier.

• Active crossovers require additional wiring for power and ground connections, but give you much more flexibility and fine-tuning control over your music. Like in-line crossovers, active crossovers cut out unwanted frequencies before the amp has to boost them so it can focus only on the frequencies you want to hear. Active crossovers usually also have volume controls on every channel or pair of channels so you can keep all the "voices" of the different speakers in balance. Some active crossovers include other sound-processing features like equalization for tweaking the sound to your personal satisfaction.

If you plan on expanding your system in the future, it's wisest to go with a separate outboard crossover, instead of relying on one built into your amplifier. While these built-in crossovers work well, they don't offer the total system control of an outboard unit. Also, if you ever upgrade your amp, you don't have to give up your crossover.

Why get active?

A passive crossover steps into the signal path after your amplification. It's a capacitor or coil usually installed right on your speaker lead. Since it is modifying a signal that has already been amplified, using a passive crossover wastes power. Also, speakers actually change their impedances when playing which also changes a passive crossover's crossover point, or frequency response, leading to inconsistent sound definition, especially around the vocal regions.

Kicker 03KX2 active 2-way electronic crossover

On the other hand, an active electronic crossover processes your audio signal before it reaches your amplifier, so it's unaffected by speaker impedance and makes your system far more efficient. Installed at the preamp level, it lets your amp concentrate its full power solely on those frequencies it passes to your speakers.

A digital crossover uses a menu screen instead of knobs and switches, giving you more filtering options and letting you set your crossover points with much more precision. You can also store different crossover settings in presets, which can be useful for car audio competitors.

Its only potential disadvantage is that since it requires +12V, ground, and turn-on connections, an active crossover presents more of a challenge to install and set up than a passive one. But with a little time and care this shouldn't be a problem, and the rewards and advantages of an active crossover make it clear why you'll find one in virtually every competition-level car audio system. Likewise, stereo systems tuned for high-quality sound will make use of crossovers in order to keep the speakers playing clean and clear.

Tuning your system

Varying your crossover points is one approach to "tuning" your speakers. You can expect this adjustability from just about any active crossover. Setting crossover points also helps define the overall flavor of your system.

Setting your low-pass filter above 100 Hz gives you the type of boom many hip hop fans are looking for, while pushing it down to 80 Hz tightens up your bass and improves front soundstaging. Because each output channel on an electronic crossover usually has its own level control, you can even use this component to compensate for varying efficiency ratings among your speakers.

Let there be music

Let's look at an example. Take a simple 3-way crossover network:

• lowpass filter with a crossover point at 80 Hz;
• highpass filter with a crossover point at 3,000 Hz;
• bandpass filter with a low crossover point at 80 Hz and a high crossover point at 3,000 Hz. (All three components use 6 dB/octave slopes.)

You hop into your ride, slip in a CD and suddenly a hefty dose of unadulterated Dave Matthews Band is headed straight for your speakers. The lowpass gobbles up Carter Beauford's kick drum and the low notes on Stefan Lessard's bass, and passes these tones below 80 Hz to your subwoofer system.

Meanwhile, your highpass sends cymbal crashes and acoustic guitar harmonics to your tweeters, while limiting frequencies below 3,000 Hz at the rate of 6db/octave. And Dave's vocals, Leroi Moore's sax solos, Boyd Tinsley's violin, and other sounds between 80 and 3,000 Hz find their way through the bandpass crossover to your midrange drivers.

The crossover assigns the proper frequencies and levels to the various speakers in your vehicle, the pieces of the sonic puzzle fit together perfectly, and DMB sounds righteous. It's all good.