How To Set Crossover Frequency For Car Audio System

Sound enthusiasts often face the challenge of figuring out how to set crossover frequency for theirw car audio system. To solve the puzzle of dividing sound waves on any type of car audio system, let’s talk about what crossovers are and how they work.

A crossover filters unwanted sound waves so that they are not sent from one frequency range to the other. It allows you to send each speaker the ranges that it will play most efficiently. In other words, each speaker is given the frequency group(s) with which it reproduces sound in the best way. This ultimately improves the entire audio system’s volume and sound quality.

How you set these filters depends on the type of sound system you use. But there are generally three settings to determine how a crossover produces results.

Filters To Set Crossover Frequency: The Big Three

  • Frequency – the level at which the filter will start to function. It’s measured in Hertz (Hz)
  • High-pass, Low-pass, or Band-pass – determines whether certain ranges will be blocked or allowed to pass through the filter.
  • Slope or Q-Factor – determines the rate at which the audio system’s volume will diminish as the frequency extends past the crossover point. It is measured in decibels (dB) per octave, and the most common slope options used range between 12 dB per octave and 24 dB per octave.

A slope of 12 dB per octave is a more gradual cut-off. It’s mostly useful in sedans that have subwoofer(s) installed in the trunk because the car’s rear seat acts as a filter and can reduce upper bass range amplitude. To counter this, this slope will allow more bleed-through of frequencies.

A slope of 24 dB per octave is considered a more abrupt cut-off. It’s great in open vehicles such as wagons, hatchbacks, and SUVs. The bass does not filter through the seat material. Since this slope is more abrupt, you can safely use a slightly lower crossover point between the midrange and the tweeter.

This article explains how to use these three settings to achieve the best sound reproduction.  We will use the term range(s) to refer to frequency range(s), and “crossover” will be used interchangeably with “filter.”

When determining the best setting for a sound system, it’s important to know the frequency range of the speaker as well as that of the subwoofer. Usually, the documentation accompanying the speakers has the necessary information. If your documentation doesn’t yield the information you’re looking for, you can rely on two general rules about how to set crossover frequency on your car stereo setup.

General rules about how to set crossover frequency 

  • For any subwoofer, the highest frequency it can handle is the highest level that should be used for filter settings.​
  • For any speaker, the lowest frequency that it’s able to handle is the lowest level to which you should set its crossover.

Settings for Different Car Audio System Configurations

1. Front components with passive crossovers and subwoofer(s)

With this kind of audio system, a High-Pass Filter (HPF) can be used. The filter will sufficiently split the frequencies between the midrange drivers and the tweeters. Lower bass sound kicks are blocked out from the midrange drivers since they are not designed to play them effectively. For the subwoofer, a Lower-Pass Filter (LPF) can be used to ensure that high ranges are not sent to the subwoofer.

You can switch the slope options (if adjustable) to achieve the sound quality that pleases you. The most common slope options for many types of car audio systems are 12 dB per octave (green) and 24 dB per octave (orange).

2. Front Components (passive), Rear Coaxial Speakers and Subwoofer(s)

This system is slightly different from the first system (above) in that coaxial speakers have been added. If the coaxial speakers use a crossover network, then the setting is set just like the component speakers. That is, for front component speakers and rear coaxial speakers, each should use a High-Pass Filter and a 12 dB or 24 dB per octave slope. And for the subwoofer(s), a Low-Pass Filter and the desired slope option should be used.

Most coaxial speakers come supplied with a basic filter instead of using passive crossovers. The filter blocks low sound waves from reaching the tweeter. The midrange rolls off its frequency in relation to the tweeter, but a High-Pass Filter should be applied to block lower groups.

The two stereo systems discussed above are the most common audio system configurations used in cars. The recommended settings are based on the assumption that the speakers have a diameter of at least 5.25 inches. For smaller speakers, the frequency for the High-Pass Filter should be higher than 80 Hz. You can start with 300 Hz and then keep tuning it down as you listen to the sound quality. Note any signs of stress from the midrange and tune the filter up or down as needed.

There are other systems that use a more advanced configuration called an Active System. In these kinds of system design, electronic crossovers are used as detailed in items three and four below.

3. Front 2-Way Components (active) and subwoofer(s)

Here, an electronic crossover is used to high-pass the tweeter (5000 Hz), band-pass the midrange (80 Hz), and low-pass the subwoofers (80 Hz). The slope can be either 12 dB or 24 dB.

4. Front 3-Way Components (active) and Subwoofer(s)

This system uses a 3-way active front stage with a pair of tweeters; it has small midrange speakers and bigger woofers. The front stage created here is more even and efficient in sound reproduction than the 2-way component set. Here are the recommended crossover settings for this system:

Tweeters = 5000 Hz HPF; Midrange to Band-Pass = 500 Hz HPF and 5,000 Hz LPF, respectively; Woofers to Band-Pass = 80 Hz HPF and 500 Hz LPF, respectively; and subwoofers = 80 Hz LPF. 12 dB or 24 dB slope options can be used.

Other systems may have rear speakers (passive) in addition to the Front 2-Way Components (active) and subwoofer(s). The rear speakers will need a High-Pass Filter and two channels of amplification. Thus, the recommended settings are an HPF (5000 Hz) for the front tweeters, an HPF (80 Hz) for the front midrange, an HPF (80 Hz) for rear speakers, and 12 dB or 24dB slope.

If rear speakers (passive) are added to this system, the settings will change a bit. Band Pass to front midranges would use a 5000Hz LPF and a 500 Hz HPF respectively. Band Pass to front woofers should use a 500 Hz LPF and an 80 Hz HPF respectively. Other settings remain the same. Since rear speakers use a passive crossover here, only 2 channels of passed amplification is required.

The understanding of how to set crossover frequency for a car audio system starts with knowing how the audio system is configured. You need to know the kind of front and rear speakers that the system features. As illustrated above, the type of speakers determines the High-Pass, Band-Pass, and Low-Pass filters, as well as the frequency to use.

Fine tuning is the most important thing. You can use these recommendations as a guideline, but the final settings depend on your fine-tuning and the quality of sound you find most pleasing. Have fun!