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Answers to crossover questions
An active 2-way electronic crossover
Q: What's a crossover and do I need one?
A: For a more complete answer to the first part of this question, you'll want to check out our How to Choose a Crossover article. A crossover divides an input signal into two or more outputs of different ranges of frequencies, so tweeters, speakers, and subs will each get only the range of frequencies they were designed to play. Frequencies outside each designated range are attenuated or blocked.
Every speaker system needs a crossover of some type. Component speaker sets come with separate outboard crossovers, many with tweeter level selectors. Every full-range, coaxial speaker — with its tweeter mounted in front of the woofer cone — already has a tiny crossover network built into it somewhere.
If you want to run an "active" system, however, you'll need a more sophisticated crossover. In an active sound system each driver (tweeter, woofer, sub) has its own channel of amplification. This dramatically increases the available power, dynamic range (softest to loudest sounds), and your control of the system’s tonal response over the whole audio spectrum.
Almost all amplifiers come with built-in high- and low-pass filters that can serve as the crossovers in a component system. But these filters are small accessory features built into the amps and are often more inaccurate with less fidelity than a separate, dedicated electronic crossover.
An active crossover gets wired between the receiver and amplifier and cuts out the unwanted frequencies before the amp wastes energy boosting them, so the amp can focus on only the frequencies it's supposed to amplify. Active crossovers usually have volume controls on every channel or pair of channels so you can keep all the “voices” of the different drivers in balance. Some active crossovers include other sound-processing features like equalization for further tweaking of the sound to your personal satisfaction.
In a hypothetical 4-way active car audio system the original full-range audio signal might be crossed-over 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 Hz are handled by the tweeters.
Keep in mind that the crossover points listed here are for example only and do not apply to every car or speaker system 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.
The passive crossovers from a set of high-end component speakers
Q: What's the difference between passive and active crossovers?
A: Short answer: an active crossover needs power — a passive crossover does not.
Passive crossovers go between the amplifier and the drivers (tweeters, speakers, and subs). A passive crossover circuit is built with coils, capacitors, and resisters beefy enough to handle the high output power of most amplifiers. Some passive crossovers include a tweeter level switch, which gives you some control over how loud the tweeter plays relative to the woofer. A disadvantage of using passive crossovers is that they filter out frequencies already amplified, creating extra heat and lowering speaker efficiency.
An active, or electronic crossover goes between the receiver and the amp. It handles low-level preamp signals with its solid-state circuitry to cleanly divide the signal and send each band of frequencies in the right direction. Active crossovers are usually adjustable (you can select the crossover points) and often have other features like bass boost circuits for subwoofers. Another bonus when using an electronic crossover is that you can independently control the relative volumes of all your different drivers.
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. You connect the speaker wire coming from your amp to the crossover's input. Then the tweeter gets wired to the tweeter output, and the woofer to the woofer output. That's it. The most challenging part of installing a passive crossover may be where to mount it, but most crossovers are small enough to fit inside your car door near the woofer's location.
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. A distribution block is a good way to get power for your crossover via the same main power cable as the amp does. You'll also need a solid, noise-free grounding point — it's generally best to ground your crossover at the same place as your amp.
Your electronic crossover also requires a turn-on lead to trigger it to turn on when you power up the receiver, and you can either run that wire to the receiver or daisy-chain it to the amp's remote terminal. You'll route the audio signal from your receiver to the inputs on the crossover via RCA patch cables. You then run more patch cables from the crossover outputs to the amplifier inputs — highs to the tweeter amp, mids to the woofer amp, and bass to the subwoofer amp, for example.
The -3dB switch lets you take the edge off the highs
Q: What's the little selector switch on my passive crossover for?
A: Many component systems have passive crossovers with 2- or 3-way tweeter level switches included. Ideally, a crossover will put out the same level of signal, or volume, to the tweeter as it does to the woofer. But many people find that sounds unbalanced and too shrill and bright. Many speaker manufacturers recognize that and put tweeter attenuators in their crossovers. The settings should include "0 dB," when the tweeter level is the same as the woofer; "-3 dB," for a little attenuation; sometimes "-6 dB," for a lower tweeter level; and sometimes even "+3 dB," for those who like it brighter.