Do You Need Car Audio Crossovers?

What you should know about car audio crossovers

Car audio crossovers are probably some of the most poorly understood audio components out there. Since they aren't absolutely necessary, it's pretty easy to just gloss over the subject altogether when building or upgrading a car audio system. Head units, amplifiers, and speakers get all the good press, but that doesn't mean crossovers aren't important as well.

Illustration of speaker producing sound waves and music notes.
 Alex Bond/Getty

In order to understand what a crossover is, and whether or not a car audio build actually needs one or more, it's important to first understand some very basic principles that underpin car audio crossover usage.

The underlying idea is that music is composed of audio frequencies that run the entire gamut of human hearing, but some speakers are better at producing specific frequencies than others. Tweeters are designed to reproduce high frequencies, woofers are designed to reproduce low frequencies, and so on.

With that in mind, car audio newbies are often surprised to learn that every car audio system in existence actually requires crossovers at one level or another. For instance, very basic systems that use coaxial speakers actually have small crossovers built right into the speakers. Other systems, especially ones that use component speakers, typically make use of external crossovers that only pass the appropriate frequencies to the correct speakers.

The main purpose of breaking music into component frequencies, and only sending certain frequencies to specific speakers, is to achieve higher audio fidelity. By making sure that only the right frequencies reach the right speakers, you can effectively reduce distortion and help improve the overall sound quality of a car audio system.

Types of Car Audio Crossovers

There are two main types of crossovers, each of which is best suited to specific situations:

Passive Crossovers

These crossovers sit between the amp and the speakers, and they filter out unwanted frequencies. Some speakers have built-in passive crossovers. Since these crossovers are simply wired up in-between the amp and speakers, they are relatively easy to install. However, there is a certain amount of inefficiency that is inherent in passive crossovers.

Active Crossovers

These are also known as electronic crossovers, and they are both more complex and more expensive than passive units. Active crossovers require power sources, but they don’t waste power by filtering out amplified signals the way passive crossovers do.

Who Really Needs a Car Audio Crossover?

The fact is that every single car audio system requires some type of crossover in much the same way that every car audio system requires some type of amplifier. But in the same exact way that many head units include a built-in amplifier, speakers can also include built-in crossovers. In basic car audio systems, it's totally possible to get by just fine with no additional crossovers. However, there are a number of circumstances where either a passive or active unit will improve the quality of the sound, efficiency of the system, or both.

If your car audio system uses coaxial speakers, you probably don’t need an additional crossover. Full-range speakers already have built-in passive crossovers that filter the frequencies that reach each driver. Even if you add an amplifier into the mix, the built-in speaker crossovers should be more than sufficient. However, you may need a crossover if you add an amplifier and a subwoofer to that type of system.

On the other hand, you’ll typically need one or more crossovers if you plan on building a system that consists of component speakers, multiple amplifiers, and subwoofers. This is especially true if you plan on using individual amplifiers to drive specific speakers, such as your woofers or tweeters. Whether you choose active or passive crossovers, you’ll need something to keep undesired frequencies from reaching the speakers.

It's also important to note that aftermarket amplifiers typically include built-in filters that effectively act as crossovers if you're building a basic car audio system with component speakers. The high pass filter in this type of amplifier allows you to drive tweeters, and the low-pass filter allows you to drive woofers, without requiring any additional crossovers.

When an Active Crossover Can Really Help

While you can typically get by just fine without a crossover in a situation where you're just using a single amplifier, more complicated builds can really benefit from an active crossover. For instance, a 3-way crossover is a component that you actually wire between your head unit and multiple amplifiers.

In this type of scenario, each amplifier receives a specific range of frequencies from the crossover, and each amplifier is used to drive a specific type of speaker. For instance, one may drive front speakers with a high pass, another may drive rear full-range speakers, and a third subwoofer amp could drive a sub.

Do Crossovers Require Professional Installation?

Installing crossovers isn’t rocket science, but you will need a basic understanding of what you’re doing before undertaking this type of DIY project. Installing a passive crossover is relatively simple since it just involves wiring a crossover between your amp and your speakers. For instance, you might wire a passive crossover to your amplifier output, then wire the crossover's tweeter output to your tweeter and the woofer output to your woofer.

Installing an active car audio crossover is typically going to be a more complicated procedure. The main issue is that active crossovers require power, so you’ll have to run power and ground wires to each unit. The good news is that if you’ve already installed an amplifier, then you should be more than capable of installing an active crossover since the wiring isn't really any more complex. In fact, grounding your active crossover in the same place you grounded your amp will help prevent annoying ground loop interference.

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