Crossovers can be a confusing topic in the audio world, but they have a simple function. They divide the frequency spectrum into different areas and typically direct these areas to the speaker drivers that are designed to handle them appropriately.
Here we dive into what crossovers are, their different types, how they’re used in live sound reinforcement and recording studio scenarios, and when to use them. Let ‘s jump in!
What is a Crossover?
A crossover is a component of an audio circuit that divides a signal into different frequency bands to direct each band to a specific driver. This ensures each driver is receiving only the frequencies within the optimal range of its design.
Proper frequency distribution prevents distortion, improves sound quality and clarity, and protects the drivers from receiving an area of the frequency spectrum they’re not designed to handle. If frequencies aren’t properly routed to the drivers that are optimized to handle them, distortion and indistinct sound can be the least of your problems. The drivers can be damaged or even destroyed!
There are two primary types of crossovers—active and passive. Active crossovers receive external power. They have more flexibility and more precise frequency distribution and adjustment. They can be manipulated in real-time based on differing audio equipment setups and user preferences.
Passive crossovers, on the other hand, don’t need external power and are usually integrated into the audio system. They have a simpler design and are more cost-effective, with the tradeoff being lack of flexibility compared to active crossovers.
Crossovers in Live Sound Reinforcement
Live sound reinforcement is one of the most common areas where dedicated crossover units are used. There are a few reasons for this.
The first is because sound reinforcement systems employ a multi-speaker setup. Unlike studio monitors where the different drivers are housed in the same speaker enclosure, live sound systems often use a dedicated cabinet for each. Crossovers in a live sound context prevent frequency overlap and distortion which results in more balanced, cohesive frequency reproduction as signal is sent to multiple types of speakers.
Depending on the size of the sound reinforcement system something called “multi-amping” might be used. This is the practice of powering different frequency drivers with separate power amplifiers. Crossovers are especially critical in a multi-amping arrangement to precisely divide the audio signal and distribute it to the drivers and amplifiers to maximize efficiency and audio fidelity.
Crossovers can have, in theory, any number of bands—that is, any number of outputs for specific spectral ranges. Typically, crossovers feature two or three bands, though four bands are not uncommon. You can these of these as being somewhat like a collection of parallel filters: one audio source passes to all filters, and each filter has a direct output. Usually, the upper band is a highpass filter, the lowest band is a lowpass filter, and all bands in-between are bandpass filters, where the boundaries of the passband are tuned to overlap seamlessly with the highpass and lowpass filters.
Crossovers in the Recording Studio
There are two different types of crossovers used in a recording studio context. Crossovers are now typically built into studio monitors, but since professional studios typically use subwoofers for low-frequency monitoring, a crossover is necessary to properly route the low end information to it.
But when it comes to integrating them into a recording rig, line level crossovers are used. They function under the same concept, but are designed to work with line level signals. Separating the frequency spectrum with a line level crossover opens up all kinds of options for mixing and mastering. Some engineers like to use them when processing low end sources like kick drum and bass guitar to manipulate the lows and highs independently.
It’s useful in effects processing too. With a line level crossover you can isolate which frequencies to compress, like only the bass frequencies so the top range can “breathe” a little more. Or only apply an effect like chorus to the high end of a vocal while leaving the low mids and bass range alone.
Modern plugins have made it easy to process different areas of a signal’s frequency range separately, and some tools (like multi-band compressors) use crossovers in their design for specialized frequency-dependent processing. That said, a lot of mix engineers still prefer to tackle tasks like these using a line level crossover and outboard gear.
When to Use a Crossover
Live sound reinforcement scenarios aside, most of the time crossovers are built into speakers. This is the case for studio monitors and hi-fi audio speakers alike. Even if you’re adding an amplifier to the system the built-in speaker crossovers should be more than enough to properly route frequencies to the drivers. But there are times when you should consider adding a dedicated crossover. Serious audiophiles add subwoofers to their setups so they can get proper bass frequency reproduction.
When adding a dedicated low end driver and an amplifier to power it, adding an additional crossover is a good idea. This ensures that areas of the frequency range above the bass range stays out of the subwoofer.
And of course, there are plenty of creative applications for crossovers as well—it's possible to build unique approaches to audio processing by using a crossover to route different frequency ranges from an sound source to multiple independent effect processors. This is especially useful for full-spectrum, harmonically-rich sounds. For instance, you could run a heavily distorted guitar through a crossover and then apply pitch shifting to the higher frequencies and compression, further distortion, or filtering to the low frequencies. You could send a drum kit through a crossover and process the highs through a reverb and the lows through a gnarly, synthy fuzz: the possibilities are quite open-ended.
Summary
They can seem complicated at first, but the role crossovers play in sound reproduction is pretty simple. They split up the overall frequency range into sections and direct certain portions of it to the different speaker drivers that are designed and optimized to handle it. This ensures the minimum amount of distortion and the highest audio fidelity.
Whether you’re setting up a studio and learning how to get the best sound out of it or an audiophile looking for the full sonic potential and best performance out of a home system, crossovers are an invaluable audio tool that provide accurate sound reproduction in audio systems of all kinds. And of course, if you're looking for a way to experiment with sound design, they can prove to be an invaluable tool.
Brandon Stoner is a lifelong musician and audio engineer who owns more guitars than anyone needs. As a lover of all things writing and music technology, he crafts every piece with his dog Max on his lap.
