Crossovers are awesome for getting better sound from even cheap speakers. But what are crossovers, how are they helpful, and what are the best crossover settings for car audio?
In this article I’ll show you how to set crossover frequencies for your car audio system along with some other helpful info:
- How crossovers work and why they make a big difference
- The best car audio crossover frequency settings (table is provided)
- Diagrams to show you how to set your car amp crossovers
…and much more, too. There’s a lot to cover so let’s get started!
Contents
What does a crossover do? Crossover frequency, slopes, and more explained
People tend to talk about crossovers as if they totally “block” sounds you don’t want to go to your speakers. While they sort-of do, in reality, crossovers are filters that greatly reduce the amount of unwanted sound frequencies sent to speakers.
How are crossovers helpful for speakers?
Crossovers are very important for car audio as they help us deal with the poor enclosures they’re used in along with the weaknesses that small speakers have. Some of the most common speaker sizes installed from the factory or sold for aftermarket use like 3.5″, 4″, and 5.25″ sizes can be terrible for playing bass, resulting in bad sound and ugly distortion.
To make matters worse, speakers in cars, trucks, and even boats are often mounted in areas where it’s impossible to get great sound because they leak air and don’t form a good enclosure to deliver sound properly unlike home stereo speaker cabinets. That means they leak air badly and can “bottom out” easily if driven hard with bass sounds, for example.
One reason why crossovers are so helpful there is that we can use them to block terrible-sounding audio frequencies that ordinarily would cause these problems and others, too.
Understanding crossover basics
When we think about musical signals we don’t always realize the important things going on behind the scenes. In fact, you’ll almost never find a good-sounding speaker system that isn’t using one or more types of crossovers; that’s how important they are for great sound.
A crossover (audio crossover) is an electrical or electronic component circuit made up of parts that react to certain frequencies and designed to eliminate unwanted ranges of sound from reaching speakers.
Crossovers allow a desired range of sound to pass unaltered and effectively block ranges of sound past a limit called the cutoff frequency.
A crossover circuit can be used for only one single speaker channel or combined with another to separate and direct sound the best speakers suited to produce it. In car audio, the most common speaker crossovers are used in 2-way coaxial and component speakers.
Simple speaker crossovers can also be added inline with speakers to block lower-end bass as well.
What are the 3 types of crossovers in car audio?
There are 3 types of crossovers:
- Active (electronic) crossovers – work in the signal path (line-level signals)
- Passive (speaker) crossovers – work in the amplified speaker path after an amplifier
- Digital (software) crossovers – they work with sound in the digital music domain
1. Active (electronic) crossovers
An example of an external (add-on) electronic (active) 2-way crossover. These are basically the same as the electronic crossovers built into many amps you can buy today. Some offer a few more options, but unlike years gone by, they’re less and less important these days. Most amps today include what you’ll need already.
Active crossovers use electrical components such as transistor-based chips called op-amps (operational amplifiers) to behave the same way as their much bigger and much less efficient speaker crossover counterparts.
They offer a lot of benefits (especially their compact size) and can be designed to allow you to choose between using no crossover, a high-pass, or a low-pass easily. Unlike passive crossovers, they do require power to work and change the signal, hence the name “active.”
Active crossovers work with a line-level (RCA) signal either before an amp’s RCA inputs (in add-on external crossovers you can buy) or inside the amp. The signal output of an electronic crossover has to be amplified, unlike speaker (passive) crossovers that you connect between an amp and speakers.
2. Passive (speaker) crossovers
“Passive” crossovers are those that use inductor and capacitors, without a power source, to filter out sounds you don’t want to reach speakers. They’re usually used for smaller speakers like with tweeters, 2-way coaxial speakers, and component speaker systems because they’re relatively affordable in those situations.
Passive speakers aren’t used to block midrange and treble (“highs”) from subwoofers because the size of the inductors needed would be really big – and expensive, too! They’re also much less efficient than electronic ones in that case.
That’s one reason the built-in low-pass subwoofer crossovers in amps are so great.
3. Digital (software-based) crossovers
Software-based equalizers and crossovers use advanced software routines to alter sound in the “digital domain.” That means they can alter the sound (or filter it, as crossovers do) by working only with the digital musical signal. This makes them more complicated but saves spaces & money since it reduces size & the electronics required.
This type is implemented in the software code of home theater receivers, car stereo head units, or digital audio processors. Software-based crossovers usually work by implementing math-based functions that alter the signal output based on its frequency.
It’s a really complicated topic, but the basic concepts aren’t hard to understand. By using special formulas, not only different types of crossovers but also equalizers can be implemented and operate on the musical signal when its represented as a binary digital number.
This is a cost and space-saving feature as there are few, if any, parts needed to make it work. However, it usually takes more specialized microprocessors or digital signal processor (DSP) chips to do so.
What are good crossover frequencies for car audio?
Within the range of sound your ears can hear, for most cases crossover frequencies typically fall into a small range you’ll likely use for tweeters (high-pass), full range speakers (high-pass), and subwoofers (low-pass).
The truth is, there’s not a “perfect” set of crossover frequencies that work for every speaker in every vehicle. That’s basically impossible because nearly everyone is using different speakers, a different setup, and so on.
However, here are some of the most common frequencies that work well in many cases.
Recommended crossover frequency table
| Speaker/System Type | Crossover Freq. & Type | Notes |
|---|---|---|
| Subwoofers | 70-80 Hz (low pass) | Good low-pass frequency range for subwoofer bass & blocking midrange sounds. Best for pure, clear bass sound that "hits." |
| Car main (full range) speakers | 56-60Hz (high pass) | Blocks low-end bass that causes distortion or speakers to "bottom out." Great compromise between full-range sound and midrange bass capability. |
| Tweeters or 2-way speakers | 3-3.5KHz (high pass, or high/low-pass) | Most 2-way or 1-way (tweeter) crossovers use a frequency near this as most tweeters can't handle sounds below this range. Same for woofers above this range. |
| Midrange/woofer | 1K-3.5KHz (low pass) | Woofers and many midrange speakers do not perform well above this general range. They're poor for treble and a tweeter should be added. |
| 3-way system | 500Hz & 3.5KHz (Woofer/tweeter crossover points) | Similar to 2-way systems the upper freq. would be the same. Midrange drivers in a 3-way system often do not perform well below 500Hz or 250Hz in many cases. |
How to set the crossover frequency for speakers on your amp
How to set high pass filter options on your amp (for main speakers)
Most people typically use a car amplifier for one of a few basic systems:
- Driving front and rear full range speakers, no subwoofer
- Driving front and rear full range speakers plus a subwoofer
- Driving a subwoofer
For cases #1 and 2, if your amplifier has a built-in crossover option you can use the high pass crossover to block low end bass that small speakers simply can’t produce well, if at all. The end result is that you’ll be able to drive your main speakers with more volume and lower distortion.
We only want to block that certain range of bass that subwoofers can handle. We don’t want to block bass found in the lower end of midrange like from the vocals in music (for example, around 100-120Hz or so). 60 to 70Hz or so are pretty common crossover frequencies that usually work well.
Adjusting an amp’s high pass crossover
For amplifiers with adjustable crossovers, use the following steps:
- Turn off equalizer or bass boost functions
- Set the front channel or front and rear (if using both) crossover switches to “HP” or however they’re labeled for the high pass function.
- Adjust the crossover frequency control to the lowest setting (this is usually around 50Hz for most amps).
- Using a small screwdriver, turn it up slightly – about 1/8 of a turn. This should be around the 60-70Hz range.
How to set subwoofer crossover frequency options
Similarly, do the following to adjust the subwoofer frequency & crossover:
- Turn off equalizer or bass boost functions
- Set the crossover switch to “LP” or however it’s labeled for the low pass
- Adjust the crossover frequency control to the lowest setting (this is usually around 50Hz for most amps).
- Using a small screwdriver, turn it up slightly – about 1/8 of a turn. This should be around the 70Hz range
- Adjust as needed: if you’re not happy with the low-end range (the range of bass sound produced), don’t be afraid to adjust the frequency control a bit.
However, I’ve seen many cases where a subwoofer installed in the wrong type of subwoofer enclosure produces bland, poor sound. A crossover can’t fix that problem.
What crossover slope do I need? Does it make a difference?
In some cases, you’ll be able to choose from a number of crossover slopes (the steepness of the cutoff) on your amplifier or other components. As I mentioned earlier, the slope how effective a crossover is at allowing fewer unwanted sounds to reach your speakers, with higher numbers being more effective.
And as I mentioned ealier, -12dB per octave (“-12dB/octave”) is very common in car audio. While it may seem like the rule of “more is better” applies here, the truth is that most of the time a 12dB or 18dB/octave crossover slope is all you’ll need.
Why do some electronics offer more crossover slopes?
Some amps, head units, and digital processors/equalizers for car audio offer more crossover options for people who want advanced control – especially if you’re working on a high-end sound system. For example, when bi-amping speakers (using an electronic crossover and separate amp channels for the tweeter, the midrange speaker, and so on), you can take advantage of each speaker’s natural behavior and get super-detailed control over the signals you send to them.
That’s a much more advanced topic and worth its own article, by the way.
However here are the basic rules for crossover slopes that will work for 90% of people:
- A 12/dB setting is good and will do the job in most cases for subwoofers (low-pass) and full-range speakers (high-pass).
- However, 18dB/octave can be better for some subwoofers depending on your particular subwoofer, the enclosure, and how your vehicle alters the sound. In that case, experiment using the -18dB setting and see how it sounds.
- 6dB/octave is a bit poor and will allow sounds to pass that can “muddy” the sound and just isn’t good enough for bass speakers. I don’t recommend that in most cases.
Most of the time, the main goal is to have the same cutoff at the same frequency. The goal, in perfect conditions, is that the speakers match up just right so there’s not much overlap in their sound as well as no gaps in the sound.
However, it’s definitely a lot harder in the real world. In my experience, however, 12dB/octave works well and is effective enough to make a big difference in how your system sounds.
