How To Set Crossover Frequency For Car Audio System
Many drivers often face the challenge of setting crossover frequencies for a new car audio system or one that they are not used to. To solve the puzzle of dividing sound waves on any type of car audio system, it would be better to first understand 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 will reproduce sound 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 3 settings that mainly determine how a crossover produces results.
- 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 or
coupes that have subwoofer(s) installed in the trunk. The reason for this is that 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 S.U.Vs. 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 tweeter.
This article explains how to use these 3 settings in order to achieve the best sound reproduction. In the article, the term range(s) will be used 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 speaker package comes with such information.
If you can’t get the information on the documents, here are two general rules that guide how to set crossover frequency for car audio system:
- 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 above system 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 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, 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 this kind of system design, electronic crossovers are used.
Below are such systems and their recommended filter settings:
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). 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.
If rear speakers (passive) are added to this system, the settings will change a little 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 car audio system starts with knowing how the audio system is configured. You have to know the kind of front and rear speakers that the system features. As illustrated above, the type of speakers determine the High-Pass, Band-Pass, Low-Pass filters, as well as the frequency to use.There may be other recommendations that differ from the ones given here, but 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 impressive.