Q: What is a crossover and do I need one?
A: For the most complete answer to this question, you'll want to check out our crossover article. In simple terms, a crossover is like a traffic cop for audio frequencies. It filters and directs frequencies to allow only a certain range of frequencies to reach a certain speaker. Frequencies outside that range are attenuated or blocked.
Every system needs a crossover of some type. How sophisticated a crossover you need depends on how elaborate a system you're planning. If you're running just a basic system with an in-dash receiver and four speakers, then you don't need to worry about buying a crossover. Your full-range speakers already have passive crossover networks built in between the woofers and tweeters. And if you're just driving full-range speakers with an external amp, the crossover network on the speakers should be fine.
When you start adding multiple amps or dedicating an amp to driving a specific type of speaker (like a subwoofer), that's when you'll need a more sophisticated crossover.
A high-pass filter allows only frequencies above a given point to pass through. A low-pass filter allows only frequencies lower than a given point to pass through. High- and low-pass filters can be used together to create what's called a "bandpass" that will allow a certain band or range of frequencies reach a speaker.
In a hypothetical car audio system the audio frequencies might be directed as follows:
- Low frequencies (say 100 Hz and lower) go to subwoofers.
- Midbass speakers get frequencies between 100 and 250 Hz.
- Midrange speakers would see frequencies between 250 and 3,000 Hz.
- All frequencies above 3,000 are handled by the tweeters.
Keep in mind that the points listed here are not set in stone and do not apply to every car out there. The best crossover points for one vehicle might not be the best for another. It all depends on the speakers being used and the acoustic properties of the car. Most electronic crossovers allow you to choose from several crossover points.
Q: What's the difference between passive and active crossovers?
A: There are two types of crossovers — "passive" and "active" (also referred to as "electronic"). A passive crossover is basically a capacitor or coil installed on the speaker leads between an amplifier and a speaker. It sets up a roadblock to stop certain frequencies from reaching the speakers. Passive crossovers are relatively inexpensive and easy to install. Their primary disadvantage is that they tend to make your overall system slightly inefficient because they filter out signals that have already been amplified.
Your system will perform better and be more efficient using an electronic crossover, especially if you're running multiple amps. An electronic crossover is installed between your receiver or equalizer and your amplifiers. It filters and directs the frequency bands in the low level signal before they reach the amplifiers.
Active crossovers are usually adjustable (you can select the crossover points) and often have other features like bass boost circuits and phase switches for subwoofers. Another bonus when using an electronic crossover is that you can independently control the relative volume of different types of speakers.
Q: How hard is it to install a crossover?
A: Passive crossovers are very simple to install. They do not require a power connection, a turn-on lead, or grounding. All you have to do is tap into your speaker wires between your amp and speakers. If you're using a tri-way crossover to drive two speakers and a subwoofer, simply connect speaker wires from the amp to the input side of the crossover and then run speaker wire from the output side of the crossover to the speakers and the subwoofer.
Active crossovers require a bit more planning and time, but with a little effort, almost anyone can get the job done. You'll need to provide 12-volt power from your car battery to operate the crossover just as you must provide a 12-volt source of power to your amp or amps. An electronic crossover also requires a turn-on lead to trigger it when you power up the receiver. And of course, you'll need a solid, noise-free grounding point.
You'll route the audio signal from your head unit or equalizer to the inputs on the crossover via RCA patch cables. You then run patch cables from the crossover outputs (frequencies have been properly channeled to each output at this point) to the proper amplifiers.
Q: What does the phase switch on an electronic crossover do?
A: It's important to understand the difference between a reversal in "polarity" and a reversal, or change, in "phase." Polarity problems are usually caused by the positive and negative speaker wires being hooked up backwards on a speaker. They should be corrected by connecting the speaker wires properly.
Phase switches on electronic crossovers are meant to deal with a change in signal phase caused by an electronic crossover. An electronic crossover will alter the phase of the output signal by 90 degrees for every "order" of slope that the crossover uses (i.e. a 6 dB/octave, or 1st order, crossover will skew the output phasing by 90 degrees, a 12 dB/octave slope, 2nd order, will skew it by 180 degrees, and so on).
The phase switch on an electronic crossover usually changes the phase of the output signal by 180 degrees. Depending on the interior dimensions of your vehicle, how the subwoofer is mounted, and where it is mounted, the bass may sound better if the phasing switch is utilized. Sometimes it will sound better if it is not used. The higher the crossover frequency between the subs and the mid-bass, the more noticeable the difference caused by phase switch position.