Crossovers and crossover frequencies may be an intimidating language for the stereo layperson. But if you’re looking to get the very best sound out of your system, crossovers are unavoidable.
Crossovers help to separate the full frequency stream flowing to your system into the appropriate frequency ranges for each of your speakers. Without crossovers, your tweeters will try to push out the big bass signal, which they can’t, and your subwoofer will try to tweet the high-end, which it’s not designed for.
If you want superior sound, learning how to set crossover frequency for speakers is an absolute must.
- What is a Crossover (Frequency)?
- What are Crossovers For?
- How Do Crossovers Work?
- Setting Your Crossover Frequencies
- The Most Common Cut-offs for Crossovers
- Different Types of Crossovers
- Active Crossovers
- Passive Component Crossovers
- In-Line Crossovers
- A Word on Crossover Slope
- Further Reading
- Looking to Improve Your Sound System?
- How to Set Crossover Frequency for Speakers – Conclusion
What is a Crossover (Frequency)?
While a bit of this article might get technical, the name sure doesn’t. A crossover is an electric or electronic device that filters out the electronic signal headed to your speakers. As a result, each type of speaker plays only the range of sounds it was designed for. It makes the signal path crossover from a tweeter to a woofer, or from a woofer to a subwoofer.
A crossover frequency is the frequency level in Hertz that is set as a cut-off. Everything below this frequency goes to a lower-end speaker, and everything above goes to a higher-end speaker.
For example, the standard recommended crossover frequency for a subwoofer is 80Hz. In a very basic sense, this means that any frequencies lower than 80Hz will be played by the subwoofer. Anything higher will not be played by the subwoofer.
What are Crossovers For?
When a speaker gets hit by a frequency that’s too low for it to handle, the poor thing will still try. This causes it to distort and sound muddy, and generally terrible. On the other end of things, a big low-end speaker like a woofer or subwoofer is designed to handle the frequencies of lower mid-range and bass.
If you send high-frequency signals to a sub-woofer, they interfere with the bass sounds it’s meant to produce. Making it sound unclear and gross. You wouldn’t play the flute inside a tuba or blow a tuba into a flute mouthpiece and expect it to sound good. Speaker systems without crossovers are the same.
How Do Crossovers Work?
Crossovers, whether electric or electronic, work on a principle of filtering. They don’t split the electronic signal running through your wires and send a bit of it here and a bit of it there. Instead, they work to block out or at least greatly reduce parts of the signal running to different points.
Let’s use a 3.5kHz high-pass filter as an example
The 3.5kHz number refers to a pretty standard crossover frequency set for protecting tweeters from the damage and distortion that lower frequencies can cause. If you install a crossover set at 3.5kHz, it will filter out the frequencies lower than that level so that only higher frequencies reach your tweeter.
It does this by dropping out the strength of the signal in the lower frequencies. These filters use -3dB as a standard at the cut-off frequency point. From there, they will increase the number of decibels that are removed according to the crossover slope, which I will explain later, until they’re essentially inaudible and have little to no effect on the speaker.
As we’ll also see later, they don’t do this perfectly, and different crossovers have different levels of effectiveness.
Setting Your Crossover Frequencies
Since the title of this article is “How to Set Crossover Frequency for Speakers,” it’s high time I get to this part.
Most stereo systems have three types of speaker cones – tweeters, woofers, and subwoofers. These represent the high, mid, and low-ends of your sound profile. But I’m sure you know this already.
However, what you need to do when setting crossover frequencies is to select two points, or two frequency cut-offs if you like. This then separates the electronic signal into three distinct ranges.
The Most Common Cut-offs for Crossovers
Low-pass filter: 80Hz (up to 100Hz)
High-pass filter: *3,500Hz (down to 3,000Hz)
*That high pass number should look familiar to you. Earlier I used 3.5kHz as an example. Well, the “k” in kHz stands for “kilo,” which means thousand, and is used in all metric measurements (kilometer, kilogram, even kilobyte). So, 3.5kHz is the same as 3,500Hz.
Some important info
Human hearing can detect sounds at frequencies as low as 20Hz and as high as 20,000Hz. Of course, this depends on the person, their age, and their specific hearing ability. Anything lower than 20Hz is in the realm of elephant infrasound, and anything higher than 20,000Hz is getting into the range of dog whistles.
So, here’s how crossover frequencies break up an audio signal. With your low-pass set at 80Hz and high-pass set at 3,500kHz, the speakers take the following ranges:
- Sub-woofer: 20-80Hz
- Woofer: 80-3,500Hz
- Tweeter: 3,500-20,000Hz
Anything lower or higher in the signal will technically still be directed to the sub-woofer and the tweeter, respectively, but you won’t hear anything. Your dog or pet elephant might, though.
Different Types of Crossovers
Now that we know what crossover frequencies are and the standard values they’re normally set to, it’s time to talk about how to pick up and install crossovers in your system.
There are commonly three types of crossovers that are used in both home stereo and car stereo systems. These include active crossovers, passive component crossovers, and in-line crossovers. I want to explain these in detail because understanding the differences between them will help you choose what’s best for your system.
Just like the name suggests, active crossovers need to be actively powered, normally through 12V DC power. Either through an electrical connection or batteries and also need to be grounded (or “earthed” in the UK). That makes their installation more difficult. While this might be inconvenient, the positives of active crossovers generally outweigh the negatives by a long shot.
Active crossovers need power to work because they are electronic devices that filter electric signals through the use of capacitors and variable resistors. They’re wired into your system between the receiver and the amplifier so that they only handle low-power signals.
By filtering these signals before amplification, you don’t need to waste power by boosting signals and then blocking them out.
How active crossovers work
Active crossovers typically use RCA inputs. They split your signal into two pairs of RCA left and right outputs, which then go into your amp and to the individual speakers.
An active crossover will include a low-pass filter to keep the bass sound pure and clean from your subwoofer, and a high-pass filter to ensure that distortion-causing mids don’t reach your tweeters.
They may also include a band-pass filter, which cuts out both low and high ends and isolates the frequencies that will go to your main speaker set (especially in car stereo systems).
Customizing the sound
Most active crossovers give you volume controls on each of the channels running through them. Some even let you set equalization, allowing you to tweak your overall soundscape. And, of course, they allow you to set your crossover frequencies to the exact points that sound best in your system.
Even though they’re more expensive, for all these reasons, I still recommend active crossovers for most stereos as long as powering them is an option. Here are some excellent crossover options.
An affordable active crossover with two filters producing three channels of output. This device also includes level controls, phase shift control, selectable crossover slope, and a bass boost that gets the most out of your subwoofer.
This is a mid-range crossover with 4-way filtering best for car stereo systems. You can set your crossover frequencies to target high, high-mid, low-mid, and low channels for added accuracy. It also includes a booming bass boost on the sub-woofer channel to make your vehicle shudder and shake if that’s your thing?
In the same range as the PRV Audio, this crossover gives three channels of output. It also features level control for your sub-woofer and bass boost up to a whopping +16 decibels.
Passive Component Crossovers
Passive crossovers, on the other hand, are perhaps more convenient. This is because they don’t need to be powered and are simple electric components. They use inductors and capacitors to filter out unwanted frequencies and are pretty basic technology.
This is what you’ll find built into 2-way and 3-way bookshelf and floor-standing speakers. Passive component crossovers are installed beyond your amplifier in the speaker lines.
Examples of Passive Crossovers
With a 2-way component crossover like the Audiopipe CRX-203s, your signal is split into a high-end for your tweeters and a low-end for your woofers. Additionally, with a 3-way crossover like the CRX-303s, you get three output ranges for your subwoofer, woofers, and tweeters. The crossover frequency is generally preset, so that takes some of the control out of your hands.
The other major downside of passive component crossovers is that they’re wired in after the amplifier. Meaning that you need to use power to boost your signals only to then filter out a lot of that signal.
This wastes power as heat and also reduces the overall power potential of your system. On the other hand, these crossovers are cheap, incredibly easy to install, and don’t need power to work.
The third option for crossovers is in-line crossovers. The name comes from the positioning in your system. These crossover units are placed between your receiver and your amplifier in the same way that active components are.
Because of the placement before your amp, they work with low-power signals. This helps to solve the issue of wasting power to heat as you find with component crossovers.
However, the main difference between in-line and active crossovers is that in-line ones are very basic, and their crossover frequencies are preset. This gives you less control over your sound profile, but it does make them cheap and easy to install.
Using in-line crossovers
Generally, in-line crossovers are RCA in and out and connect from your receiver directly into your amplifier. You just look at the preset crossover frequency you want. And then select high-pass (meaning everything lower will be filtered out) or low-pass (meaning everything higher gets filtered out).
Examples include Harrison Laboratory’s FMOD 70 Hz Low Pass Crossovers, which isolate only the signal below 70Hz, or their FMOD 100 Hz High Pass Crossovers, which let only signals over 100Hz through.
These are simple and affordable RCA plug-in devices used extensively in car stereo systems. Furthermore, they come with multiple drivers of different sizes.
A Word on Crossover Slope
One more thing that I haven’t mentioned yet is crossover slope. Think of a diagram showing volume (y-axis) over frequency (x-axis). You would want to see a nice level line on one side of a crossover frequency and a pretty sharp drop off down to zero on the other side.
This is the crossover slope, and what it measures is how effective a crossover is at filtering out unwanted frequencies. So, you might expect a very sharp slope to be best, and in general, you’re right. But you can get away with a shallower slope on high-pass filters than low-pass filters.
Slope is measured by how many decibels the sound drops over an octave. Generally, you’re going to find crossovers with slopes of -6dB, -12dB, and -18dB. Going from tweeters to your woofers, -6dB is generally okay, although -12dB is pretty standard. For subwoofers, -12 or -18dB will produce the cleanest, purest bass sounds and prevent muddying.
If you want to get deeper into the design and planning of a great sound system, I recommend Loudspeaker Design Cookbook by Vance Dickason. He goes into everything you need to know on how to set crossover frequency for speakers. From speaker selection to placement to crossover installation and frequency selection and a whole lot more.
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How to Set Crossover Frequency for Speakers – Conclusion
We’ve seen what crossovers do and the different types you can incorporate into your car or home stereo system. I also discussed what crossover frequencies are and which are the most standard frequencies to choose.
However, now that you know what setting crossover frequency does, you can experiment with your system. This will allow you to find the best points for your speakers using active, passive, or in-line crossovers.
By limiting the signal to the right frequencies, you can get the most out of each speaker in your stereo system. Your tweeters will shine, your woofers will sound full and clear, and your sub-woofer will have the purest, strongest bass tone possible. Everything will be perfectly tuned and performing at its very best, thanks to crossovers and a little patience.
Best of luck, and happy listening.