What Is A Good Crossover Frequency For Home Or Car Audio Speakers?

What is good crossover frequency featured image

Crossovers are one of the single most helpful parts or features for getting great sound in car or home audio systems. However, using them the right way can leave you scratching your head if you don’t know the basics.

On that subject, what is a good crossover frequency for speakers in your car or home audio system? That’s what you’ll learn here.

In this article I’ll explain:

  • How crossovers work and why they make a big difference
  • The best crossover frequencies for car audio amps, speakers, and subwoofers
  • Recommended crossover frequencies for small, medium, and large home stereo and home theater receiver speakers including subwoofers
  • What to know about crossover slopes and which you should use

Let’s get started so you can enjoy better sound right away!

Contents

The basics: What does a crossover do? What does crossover frequency mean?

Crossovers and crossover frequencies explained diagram

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 aren’t blocks but instead filters that greatly reduce the output level of certain sound frequencies sent to speakers.

How are crossovers helpful for speakers?

Diagram of man listening to speaker with crossover vs without a crossover

Crossovers are very important for audio as they help us deal with the weaknesses of commonly available speakers as well as poor installation environments. For example, some of the most common speaker sizes used in cars such as 3.5″, 4″, and 5.25″ sizes can be terrible for playing bass. They end up with bad sound and ugly distortion when driven with low-end bass and more power.

To make matters worse, many speakers aren’t used in proper enclosures. This ends up giving poor sound and distortion at higher volumes because they leak air and don’t properly trap sound waves like others. That means they can “bottom out” easily if driven hard with music with “thump” and hard bass.

An excellent solution to these and other problems is to completely remove that area of sound that causes poor sound quality. This lets you drive the speakers with more power yet get more clarity and volume from them – even cheap speakers!

2-way and 3-way speakers become possible

Additionally, 2-way and 3-way speakers rely on crossovers to act as a divider between the speakers, resulting in excellent sound thanks to limiting the range of sound each produces.

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 crossovers; that’s how important they are for great sound.

A crossover is an electrical or electronic component circuit made up of parts that react to certain frequencies and is designed to prevent 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 a single speaker channel or combined with others to separate and direct sound to others, too. In car and home audio, the most common speaker crossovers are used in 2-way coaxial speakers, component speakers, and 2-way speaker cabinets.

There are 3 types of crossovers you’ll find in home or car audio:

  1. Active (electronic) crossovers – work in the signal path (line-level signals)
  2. Passive (speaker) crossovers – work in the amplified speaker path after an amplifier
  3. Digital (software) crossovers – they work with sound in the digital music domain

Electronic crossovers

Electronic crossover functional diagram showing the basic blocks of operation

Active (electronic) crossovers use tiny signal amplifier chips called op-amps (operational amplifiers) to act similar to much bigger and far less efficient speaker crossovers.

Not only are they much smaller in size, but they can also be designed to allow you to choose between using no crossover, a high-pass, or a low-pass filter easily using a slide switch. Unlike passive crossovers, they do require power to work and change the signal, hence the name “active.”

These types work with low-level (RCA) signals 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.

That means you’ll still need to use an amp to drive speakers with them.

Speaker crossovers

Home and car stereo speaker crossover examples illustrated and labeled

Examples of car and home speaker “passive” (non-powered) crossovers. These are circuit boards using electrical components to block unwanted sound frequencies from going to speakers not best for producing them. This effectively separates splits the incoming sound signal into 2 or more and sends them to the speakers as needed.

“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 typically used for smaller speakers like with tweeters, 2-way coaxial speakers, and home theater 2-way speakers because they’re cost-effective and can deliver great sound.

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.

Electronic crossovers are typically used in subwoofer amps because of the cost and size savings – as well as better sound altogether.

Digital (software-based) crossovers

Example of home stereo digital subwoofer crossover menu display

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.

Crossover frequency vs music range chart

Crossover audio range chart diagram

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. 

What are good crossover frequencies for home audio?

Man teaching about good crossover frequencies for home audio

Since different people have different needs, I’ll cover the general best crossover frequencies for ome stereos and home theater receiver speakers in a table below.

One thing to remember is that these are general guidelines that should fit most people’s needs. However, just like anything else, what sounds good to one person or with one home audio system might not sound good for another.

Feel free to try out and adjust the crossover levels recommended here for what sounds best to you. Ideally, the crossover speaker frequencies (for example, for the main speakers and subwoofer) will blend seamlessly and there won’t be any “gaps” in the sound. If there are, you’ll need to keep tweaking it until that problem is removed.

TIP: I recommend you set any equalizers, bass boost, or “loudness” controls to off before adjusting the crossovers to be sure those don’t interfere during adjustment.

Home stereo crossover frequency table

Speaker/System TypeCrossover Freq. & TypeNotes
Subwoofer 80 Hz (low pass)

Good low-pass frequency range for subwoofer bass & blocking midrange sounds. Best for pure, clear bass sound that "hits." *For THX Certified/non THX Certified 80 Hz is advised, but test 80-120H for the best sound.

Tower/main front speakers [4", 5.25", or 6" woofers] 60-80Hz (high pass)

Blocks low-end bass that causes distortion & speakers to "bottom out." Great compromise between full-range sound and midrange bass capability. Works best complimented with a subwoofer.

Tower/main front speakers [8", 10" or larger woofers] 40Hz (high pass) or "flat" (full-range)

Larger woofer cones are usually much better at handling deeper bass. Also, home theater surround systems normally send very low bass to the subwoofer as well.

Small center, surround, or bookshelf 100-120H (high pass)

Many surround or center speakers use drivers not suited for lower bass - only midrange and above.

Mid-sized center, surround, or bookshelf 80-100Hz (high pass)

Better suited for playing bass notes slightly below vocals and notes around 100Hz, but not good for lower bass.

Large sized center, surround, or bookshelf 50 or 60-80Hz (high pass)

Larger speakers of this type can often handle a bit more bass nearly down to, but not including, the subwoofer range. Try 50Hz for larger woofers and 60-80Hz for others if unsure.

On-wall or mini satellite/surround type speakers 150-200Hz (high pass)

Many can't produce much bass but instead midrange and above. May distort badly if sent low bass notes so be sure to use a HPF as recommended.

What are good crossover frequencies for car audio?

Man teaching about good crossover frequencies for car audio

Car audio speakers are somewhat different from home audio in that they often suffer from terrible enclosures which aggravates the problems they have when producing certain sounds. The crossover frequencies below are general guidelines that work well in most cases but be aware you may need to tweak them.

For example, small speakers with no real enclosure may have horribly “thin” sound – in that case you may need to raise the high-pass filter (HPF) frequency even higher to minimize sound problems. Use these as a starting point, see what you get, and go from there.

TIP: Disable any equalizers, bass boost features, or “loudness” controls to off before adjusting the crossovers to be sure those don’t interfere during adjustment.

Also, be aware that a crossover can’t compensate for a subwoofer that’s poorly matched to a speaker box. It’s very important for good bass sound to have subwoofers in an enclosure of the right size and quality.

Car audio speaker & amp crossover frequency table

Speaker/System TypeCrossover Freq. & TypeNotes
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.

What is a good crossover slope? Does it matter?

What crossover slope do you need image of man thinking

In some cases, you can choose from a number of slopes (the steepness of the cutoff) on your amplifier or other components. As I mentioned earlier, the slope controls the steepness of a crossover filter, or how strongly it reduces & blocks sounds you don’t want to reach your speakers.

And as I mentioned earlier, -12dB per octave (“-12dB/octave”) is very common for both car and home audio systems. While it may seem like the rule of “more is better” applies here, the truth is that most of the time a 12dB/octave crossover slope is all you’ll need.

I’d had some success using an 18dB/octave slope with subwoofers, but aside from that, it won’t usually make much of a difference – at least not enough you’ll take notice of.

Here are a few tips to help:

  • I don’t recommend a -6dB/octave crossover for speakers, especially small main ones. That’s because a 6dB slope still allows a lot of bass to pass when using tweeters and small speakers.
  • 12dB is almost always fine. 18dB is fine too, but you likely won’t notice much difference in most speaker systems.
  • Don’t spend extra money, time, or effort for a more advanced crossover unless you really need the features. The majority of the time, even for amplified speaker installations at home or in the car, a standard crossover works great when properly set up.

Why do some car or home audio components have different slope settings?

Close up image of a car amp crossover controlsExample of a car amplifier without crossover slope options. If it’s not labeled near the controls, it’s nearly always a 12dB/octave and you’ll be fine.

It’s not unusual for home & car audio stereos and amps to offer 6dB, 12dB, 18dB, and even steeper (ex.: 24dB) crossover slopes you can choose. That’s especially true for mid to high-end equipment. The extra selectable crossover slope options allow more advanced control and flexibility when working with custom audio systems.

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 eliminating waste and any audio interference a speaker crossover may cause by driving them directly without a crossover.

That can give you some of the best sound possible if you’re really wanting to pursue high-end sound using more advanced techniques.

What is a good crossover slope for car audio and home audio?

However here the best crossover slopes for most 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 it in most cases.

The main goal is to have the same sound filtering at the same crossover frequency. The goal is to have the sound put out by the speakers match up perfectly so there’s neither much overlap nor gaps in the sound between the speakers.

I don’t think I’ve installed a home or car audio speaker system yet where the -12dB per octave wasn’t able to do the job well.

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What Happens If I Use A Different Impedance Speaker On A Crossover? Can I?

What happens if you change the impedance of a speaker on a crossover featured image

Have you ever wondered what really happens if you use a different impedance speaker with a speaker crossover? It’s a great question!

As it turns out, the speaker impedance (Ohms) does make a difference for how a speaker crossover works and affects the sound. I’ll explain it all in detail in a way that anyone can understand.

Contents

What is a speaker crossover? What does a crossover do?

Home and car stereo speaker crossover examples illustrated and labeled

Top: A typical car stereo speaker crossover, with the main parts labeled. Bottom: A typical home stereo speaker crossover, which is extremely similar. (These are normally installed inside the speaker cabinet) Both use capacitors and inductors to form crossover filters and control the sound sent to tweeters, midrange speakers, or woofers for best audio sound quality.

Speaker crossovers are often called “passive” crossovers because they pass signals without need a power supply unlike electronic (“active”) crossovers. They work using passive components: capacitors and inductors.

A speaker crossover is an electrical circuit that uses inductors and capacitors to filter a speaker signal and split it among 1 or more outputs. The outputs depend upon the frequency response of the speakers used.

They’re different from electronic crossovers in that instead of being connected to the signal path (RCA cables, for example) speaker crossovers are connected to the output of amps or stereos. The speakers are then connected to the crossover’s speaker connections.

2 way speaker system and crossover diagram

One of the most common speaker crossover types in use today: A 2nd-order 2-way speaker crossover with tweeter and midrange/woofer outputs. Inductors are represented with an “L” symbol and capacitors with a “C” symbol. Speaker crossovers work to separate the sound sent to certain speakers for improved sound, lower distortion, and to control over how speakers are used. For example, they block bass that tweeters can’t produce and highs that a woofer can’t produce well.

Inductors and capacitors have some really interesting (and really useful!) properties when an electrical audio signal flows through them:

  • Inductors are coils of wire that have more resistance (called impedance, in this case) to a high-frequency signal than a lower one. Therefore they filter out higher sound frequencies when connected in series.
  • Capacitors have more “resistance” to a low-frequency signal than a higher one when in series. The lower the frequency, the less signal that is allowed to pass.

When a capacitor or inductor has a signal applied to it past a certain frequency range called the crossover frequency, corner frequency, or cutoff frequency, the amount of signal it allows to pass is lowered, making it act like a filter.

This means the speaker will receive less and less of the speaker signal that we want to block, reducing the volume output for that unwanted range of sound. It’s important to understand that the frequency at which this happens depends on the speaker impedance (Ohms load) connected.

Speaker crossover orders (slopes) and designs

Image of a tweeter used with inline bass blocker capacitor speaker crossover example diagramWhen used in series with a tweeter, a crossover filters out damaging and distorting bass that it can’t handle. When used alone, a single capacitor is a 1st order (single-stage) crossover with a slope of -6dB per octave – the most basic level.

Crossovers come in different designs for different types of audio tailoring & performance levels, but they all work in the same basic way. They’re designed with “orders”, or stages, which when added make their filtering even better at blocking unwanted sounds from reaching speakers.

Crossover slope diagram and examples illustrated

For example, here’s a list of common order crossovers you’ll often see:

  • 1st order: Not very steep -16dB/octave), consists of a single capacitor or inductor in series with the speaker.
  • 2nd order: Better -12dB/octave filtering, using TWO components for each speaker.
  • 3rd order: Even better, with -18dB/octave filtering, using THREE components for each speaker.

Crossover filters are always multiples of 6 decibels (dB) because of how the components work. A “steeper” (higher) crossover order just means it’s more effective at blocking the range of sound frequencies we don’t want to reach the speaker.

What is speaker impedance? How does speaker impedance work?

What is speaker impedance diagram

Speaker impedance is the total amount of resistance a speaker has due to both the resistance of its wire coil and the inductance of the wire coil loop. Impedance is rated in units of resistance called Ohms.

Just like you can’t have a short circuit across a battery, an amp or stereo needs some amount of speaker load impedance to limit how much electrical current the radio or amp tries to supply.

Unlike a straight wire that goes from one point to another when you hook up power, the voice coil’s wire winding forms a loop that has an electrical property called inductance. Inductance is a bit different from resistance as it changes as the frequency changes. It’s called inductive reactance.

For nearly all speakers, this means that the real impedance (the total resistance) actually changes somewhat as the music plays.

When we refer to the impedance of speakers, most of the time we’re referring to the category (general Ohms range) of the speaker used to match home or car stereo amplifiers.

Resistance measurements, in units of Ohms, are sometimes shown by using the Greek symbol Omega: “Ω”

How does speaker impedance work?

how does speaker impedance work diagram

When a musical signal (made up of alternating current) drives a speaker it creates magnetic fields as electrical current flows through the tightly wound wire voice coil. What’s interesting is that a coil of wire develops magnetic fields around it that resist the flow of current when this happens.

That’s where the frequency-dependent part of a speaker’s impedance comes from.

(This also happens with other electrical devices too, like motors, engine spark plug coils, and more. They also deal with electrical resistance as alternating current (AC) is applied.)

What happens if I use a different impedance speaker on a crossover?

Crossover shift due to speaker impedance change explained diagram

Diagram showing what happens when you change the speaker Ohm load connected to a crossover: crossover shift occurs. This means because it was designed for a different speaker impedance, the frequency at which it works changes.

Crossover shift when using different impedance speakers

As I mentioned earlier, speaker crossovers are based on parts (capacitors and inductors) that work as filters according to the speaker load they’re connected to. Because of this, when you change the speaker impedance you change the crossover frequency and the sound.

You may notice several problems after doing this:

  • A “harsh” sound from woofers or midrange speakers. Tweeters may sound distorted and being to “break up” the sound at volume.
  • A “thin”, weak quality to the music.
  • Gaps in the sound ranges you should be hearing.

Speaker crossovers can only be used with the speaker impedance they’re designed for or they won’t sound the same.

For example, using an 8 Ohm home speaker crossover with a 4 Ohm car speaker won’t work correctly. That’s because the part values were chosen for one impedance only. When you change that, it dramatically changes the crossover frequency!

What happens to a crossover when I half the speaker impedance?

When you change the speaker impedance connected to a speaker crossover it can significantly shift the crossover’s cutoff frequency. As a general rule:

  • Halving the speaker impedance (ex.: 8ohms to 4 ohms) doubles the crossover frequency (Ex.: 3.5kHz goes to 7kHz)
  • Doubling the speaker impedance (ex: 8 ohms to 16 ohms) halves the crossover frequency (Ex. 3.5kHz goes to 1.75kHz)

We don’t want that because it allows the speakers to be sent a sound range they’re not suited for and sounds bad. In the case of tweeters, bass & midrange are bad because they can’t produce it properly. In fact, after a certain power level tweeters can be damaged when driven hard by bass frequencies.

Similarly, many woofers can’t produce high frequency sounds well and can sound terrible.

Normally, if you change the speaker Ohms load you’ll have to replace the speaker crossover as well to match the Ohms load.

However, there is a workaround that offers some hope…

How can I use speakers with a different impedance? Is it possible?

How to use a different speaker impedance with crossover diagram

The great news is that it is possible to use a different speaker impedance with a speaker crossover it’s not designed for! There are some compromises you’ll have to make, though.

How to match a different speaker impedance to a crossover

This is actually pretty simple! To match a speaker impedance to a crossover:

  1. Case #1: speaker that has a lower impedance: You can add a resistor in series with the speaker to bring the total Ohms load up to what the crossover needs. You’ll need a resistor with enough power handling (called a “power” resistor) to avoid it overheating (see below).
  2. Case #2: speaker that has a higher impedance: You can add a resistor in parallel with the speaker to bring the total Ohms load down to what the crossover needs. 

Examples:

  • You can use an 8 ohm speaker with a 4 ohm crossover by connecting an 8 ohm resistor in parallel with it. The end result is 8 Ohms/2 = 4 ohms the crossover will see.
  • You can use a 4 ohm speaker with an 8 ohm crossover by connecting it in series with a 4 ohm resistor. The end result will be 8 ohms total seen by the crossover.

What is a power resistor?

Audio power resistor examples

Examples of power resistors commonly used with speakers. Unlike the tiny resistors used in electronics, these can handle much more power and won’t burn up due to heat. They’re available from electronics suppliers including speaker component retailers.

A power resistor is just a larger-size resistor that can handle a lot more power & heat than the small ones commonly used on electronic boards. They’re actually fairly inexpensive, too ($5 or so for 2 to 4 in a pack) and are commonly used for custom speaker projects.

For speaker systems, I recommend using one with a power rating of 25 watts or more to be sure. For car stereos, you can often get away with around 10W to 15W, however.

The drawbacks of using resistors to match a crossover

Like I said earlier, it’s not without a compromise. You’ll have to live with a few things depending on which case you’re dealing with:

  • Adding a resistor in series with a speaker will drop the maximum power & volume available to it. In the case of a 4 ohm speaker and a 4 ohm resistor, this means you’ll lose 3 dB of volume (a tiny amount) but the power will always be 1/2 of what it used to be.
  • Adding a resistor in parallel with a speaker means the power will be split between the two. In the case of an 8 ohm resistor parallel with an 8 ohm speaker, a each side will receive 1/2 of the power formerly sent to one speaker. (Ex.: a 50W amp would now deliver 25W max to the speaker)

Ordinarily, I’d recommend using the correct crossover but if you’re “in a pinch” this solution is a great way to get your speakers going and still sounding good.

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What Is A Crossover Frequency? What Does A Crossover Do? A Helpful Guide

What does a crossover do? What is a crossover frequency? Featured image

Wondering what crossovers do and what a crossover frequency is? Trust me, I know – it can be a bit confusing at first.

Crossovers are incredibly important for a great-sounding stereo system whether in your home, car or nearly anywhere that speakers and an amplifier are used.

In this detailed post, I’ll explain what they are, how they work, and much, much more in a way that anyone can understand.  

Contents

Infographic – Audio crossover facts

What does a crossover do infographic diagram

What is a crossover frequency? What does a crossover do?

Crossover frequency and crossover basics summarized
  • Crossovers are used to separate an incoming musical signal into 1 or more outputs. They offer a way to “cut off” certain sound ranges to send the best range to each type of speaker (For example, tweeters and woofers in a 2-way speaker system)
  • A crossover works using the principle of electronic filters to filter out (block) a range of musical sound frequencies as desired.
  • A crossover frequency is the sound frequency that starts the cutoff point for crossover filters. It’s the frequency point at which signals are reduced by 3 decibels (represented as -3dB)
  • A crossover’s outputs are the signal ranges allowed to pass such as high-pass (lower frequencies are blocked) and low-pass (higher frequencies are blocked)
  • There are 2 types of crossovers: active (electronic) and passive (speaker) types. Both types are very commonly found in home, car stereo, and professional audio systems

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 1 or more types of crossovers.

That’s how important they are!

A crossover (audio crossover) is an electrical or electronic assembly that separates a musical sound source and provides outputs best suited for certain types of speakers.

There are 2 types of crossovers:

  • Active (electronic) crossovers
  • Passive (speaker) crossovers

Crossover frequencies explained

Shown: One of the most common crossovers used directly on speakers and the crossover frequency as a real-world example. As tweeters can’t produce bass sounds, they distort and can even be damaged by heavy bass. Using a crossover, therefore, makes it possible to block (filter out) unwanted sounds below the crossover frequency. (Shown is a typical frequency used at 3,500 Hz [3.5 KiloHertz]).

The crossover frequency is the sound frequency point at which sounds after that will be greatly reduced, effectively blocking them.

We use it as a reference point at which the output to a speaker (or the input to an amplifier, when using active crossovers) is reduced by 3 decibels (-3dB). Normally the crossover frequency is used as a starting point in mathematical computations for crossover design.

In the world of electronics, it’s also sometimes called the corner frequency or cutoff frequency.

What’s the simple answer?

All sound frequencies after the crossover frequency are cut more and more past it, with an increasingly steep reduction – to the point where they’re almost completely blocked.

In other words, a crossover filters out a range of sound you’d like to prevent reaching speakers, starting at the crossover frequency.

What does sound “frequency” mean?

Diagram explaining sound frequency definitionIn this simple diagram, you can see what I mean by “frequency.” After all, the word simply means “how many times something happens.” Likewise, sound frequencies are assigned a number by the number of times they occur per second.

When we talk about “frequency” we’re referring to a number range for the human ear. For math & engineering purposes most of the time we use the range of 20 to 20,000 Hertz (20 to 20 KiloHertz, or 20 thousand Hertz).

In reality, the human ear can only hear down to around 30 Hz and near 16 KiloHertz, although it depends on your ears.

Hertz is a label used to represent frequency in terms of cycles per second. It’s because all sound waves (and electronic audio signals too) are alternating waves that happen many times per second.

“Hz”, “KiloHertz”, “kHz” are shorter ways of writing it (Kilo = the thousands marker, as you might recall from math class).

As an example, here are some of the most common sound frequencies that crossovers help with:

  • Bass: 20-100Hz or so
  • Midrange: (vocals, instruments, and more) ~100Hz to around 3Khz
  • Treble: (high-frequency sounds) Around 3KHz to 20Khz

How does a crossover work? What is a speaker crossover?

As I mentioned earlier, there are 2 kinds of crossovers. That’s true even if they’re built into an amplifier or speaker cabinet itself. The same basic designs are used just in a different package.

1. Active (electronic) crossovers

Illustrated diagram of an electronic (active) crossover example

A typical example of a separate electronic (“active”) crossover. In this example of a separate crossover used with car stereo amplifiers (nearly identical to those used in home stereos, too) you can see the RCA jack audio inputs and the crossover’s adjustable/switchable outputs. One set of output jacks provides a high-pass signal to connect to an amp for driving tweeters or full-range speakers while blocking bass. The 2nd output is for providing a bass-only signal to the amp for woofers.

Illustrated view of a car amplifier built-in crossover and componentsA typical car amplifier’s built-in electronic crossover circuitry illustrated. Sometimes called the “front end”, an amplifier’s internal crossover section is made up of a few basic electronic parts: Variable resistors, operational amplifier chips, capacitors, and fixed value resistors. They’re designed just like separate crossovers to give adjustable features & variable crossover frequency settings.

Electronic crossovers are also sometimes called “active” crossovers as unlike speaker crossovers, they need a power supply connection to work. Also, unlike speaker crossovers, they’re used before an amplifier.

While speaker crossovers connect directly to the higher-power output terminals of an amp and then to speakers, electronic crossovers work only with small signals. They’re connected to the outputs of a stereo in most cases.

How electronic crossovers work

Image showing a typical op amp IC and low pass crossover circuit example

Left: A typical operational amplifier (Op amp) integrated circuit (IC), the Texas Instruments TL072. Right: An example of a low-pass crossover circuit using an op-amp to filter out high-frequency sounds.

Electronic crossovers may sound very complicated (and they are, at least in some ways) but they’re actually based on pretty basic principles.

They work using a variety of electronic filter circuits based around a very common electronic component: the operational amplifier (“op amp”). Op amps are tiny multi-purpose amplifiers that are very useful for amplifying or changing an input signal in many ways.

They, together with resistors and capacitors, can be used to control how a music signal is output and will block certain ranges of frequencies.

Alpine car amp electronic crossover schematic exmaple

A schematic of a typical electronic crossover. In this case, the left stereo channel of an Alpine car amplifier’s built-in crossover circuitry is shown.

Electronic crossover functional diagram showing the basic blocks of operation

When put together in a way in which you can select your preferred filter (high or low pass, for example) and adjust the crossover frequency they form a complete crossover unit.

Basically, they offer several adjustable filters so you can prevent a range of musical frequencies from going to the wrong speakers. The crossover frequency is usually adjustable using switches or dials to allow you to change it as you like.

Once an input signal is applied, you’ll get the following outputs (depending on the type, as there are many options available):

  • High-pass outputs to block bass from tweeters or to block low-end bass from main speakers. This allows more volume without distortion as small speakers can’t handle heavy bass well.
  • Low-pass outputs for bass: When used, this blocks the vocals and other higher frequency sounds that woofers and subwoofers can’t reproduce well. The result is good, clear, heavy-hitting bass.

2. Speaker (passive) crossovers

Home and car stereo speaker crossover examples illustrated and labeled

Top: A typical car stereo speaker crossover, with the main parts labeled. Bottom: A typical home stereo speaker crossover, which is extremely similar. (These are normally installed inside the speaker cabinet) Both use capacitors and inductors to form crossover filters and control the sound sent to tweeters, midrange speakers, or woofers for best audio sound quality.

Speaker crossovers are sometimes called “passive” crossovers as they don’t need an external power supply connection. They work using passive components: capacitors and inductors.

A speaker crossover is an electrical circuit that uses inductors and capacitors to filter a speaker signal and split it among 1 or more outputs. The outputs depend upon the frequency response of the speakers used.

Unlike electronic crossovers, normally they’re connected to the outputs of an amplifier and then to the speakers you’d like to use.

2 way speaker system and crossover diagram

One of the most common speaker crossover types in use today: A 2nd-order 2-way speaker crossover with tweeter and midrange/woofer outputs. Inductors are represented with an “L” symbol and capacitors with a “C” symbol. A “2nd order” crossover just means that the second stage of parts is used to make the crossover filter out the unwanted frequencies even more effectively.

Capacitors and inductors have some interesting properties depending upon the frequency of a signal applied to them:

  • Capacitors have more “resistance” (called impedance, in this case) to a low-frequency signal than a higher one. The lower the frequency, the less signal that is allowed to pass.
  • Inductors are coils of wire that have more resistance to a high-frequency signal than a lower one. Therefore they filter out higher sound frequencies.

This works because when a capacitor or inductor has a signal applied to it that’s past the crossover frequency (depending on how it’s used), the resistance increases, which reduces the speaker voltage.

This means the speaker will receive less and less of the speaker signal that we want to block.

In all cases, the part value is chosen according to the speaker “Ohms” (impedance rating) it’s planned to be used with. That’s super important!

Note: Speaker crossovers can only be used with the speaker impedance they’re designed for, or they won’t sound the same.

For example, using an 8 Ohm home speaker crossover with a 4 Ohm car speaker won’t work correctly. That’s because the part values were chosen for one impedance only. When you change that, it dramatically changes the crossover frequency!

Image of a tweeter used with inline bass blocker capacitor speaker crossover example diagramWhen used in series with a tweeter, a crossover blocks damaging and distorting bass that tweeters can’t handle. Capacitors like in this example can be used as a simple speaker crossover for tweeters.

Speaker crossovers are designed in many ways but all have the same basic design structure – only the details change.

They’re also often labeled with names like “1st order”, -6dB/octave, “2nd order”, -12dB/octave, and so on. I’ll explain a bit more about that as we go.

For now, you only really need to know that 2nd order and 3rd order crossovers are the same thing but with more crossover stages, or “orders”, added to make the filtering ability even more effective.

What are decibels and why do we use them for audio?

Diagram showing the formula for crossover voltage in decibels with example math problem solved

Crossovers (and a lot of other audio electronics & equipment) are measured using Decibels. Decibels (“dB”) are a convenient mathematical way of dealing with numbers that occur as powers of 10, unlike linear numbers, which occur in a straight line. Shown is an example of figuring out the reduction, in dB, of a crossover output.

In the real world, lots of measurements deal with things that don’t increase or decrease in a straight line (“linear”) but instead on a curve (“non-linear”, or logarithms).

I won’t bore you with heavy math here, but we use Decibels in the world of audio as a mathematical way of dealing with musical electrical signals. That’s because a lot of it happens not in a straight line but in curves.

That is, much of the audio world works with powers of 10 (logarithms, which you might remember from your algebra class). Hence the need for a way to deal with those – that’s where the dB representation comes in handy.

And it’s not just crossovers that work with decibels but even your own ears are “logarithmic”! That is, the volume your ears perceive is measured in dB, too.

What is a crossover “slope”?

Crossover slope diagram and examples illustrated

Diagram showing the crossover slope, or cutoff steepness, for the most common crossover types. Crossovers have “orders” – that is, 2nd, 3rd, or more stages that increase their ability to filter out the unwanted sounds frequencies sent to a speaker.

A crossover slope is the steepness of a crossover’s filtering ability. In other words, it’s how much a crossover’s blocking (filtering) ability is past the crossover frequency point.

Slopes, just like the crossover frequency, are determined according to a level in decibels (dB). The negative symbol is used to show they represent an attenuation, or reduction, of the signal. (Which of course is how crossovers work!)

As you might have guessed, the larger the steepness (greater the slope), the more effective the crossover is at filtering out bass sent to a tweeter, as an example. Likewise for other speakers connected to it.

In the audio world, we commonly refer to frequencies in octavesAn octave is a doubling or halving of a frequency number.

For example, when we refer to a crossover having a cutoff of -6dB per octave, we mean it will continue to cut the input signal more by a factor of 6dB for every doubling of the previous frequency.

Like this: (Low pass crossover frequency) -6dB @ 1KHz, -12dB @ 2KHz, -18dB @ 4KHz, -24dB @ 8KHz, –32dB @ 16KHz, up to 20KHz.

What are the most common and best crossover slopes?

12dB per octave speaker crossover example image

There’s a lot more to say here, but crossovers are designed to be a good compromised between complexity, price, and sound quality. While you might think “the higher order, the better” would always apply, things get much more complicated once you get past 3rd or 4th order crossovers.

Generally speaking, a -12dB crossover slope is one of the best compromises and works well for most speaker systems used today.

One reason is that it’s simple. has fewer design complications, but still gives a good cutoff ability that works great both for single speakers or 2-way speakers.

In general, the most commonly used are:

  • -6dB
  • -12dB (the most popular, by far)
  • -18dB

Electronic and 2-way speaker crossovers are nearly always -12dB models.

What is a two way speaker?

Image showing diagram with home and car stereo 2-way speaker examples

Examples of very common 2-way speakers you’ll find in either car or home stereos (in addition to other types as well). They have nearly the same things in common except that home stereo speakers are usually placed in a speaker box (speaker cabinet/enclosure) while car speakers may be installed separately in many cases. Both use a 2-way crossover to produce a very nice sound.

What are 2 way speakers?
  • 2-way speakers are a speaker system in which 2 speakers work together to produce the full range of sound. Audio from a stereo amplifier is divided between the speakers by a 2-way speaker crossover.
  • 2-way speakers are the most common type in the world, and many offer low-cost with great sound
  • These types of speakers use a tweeter for high frequencies and a woofer speaker for the midrange and bass portions of the music.
  • While the type of crossover varies from model to model, one of the most common and best-performing is the 2nd order crossover with a slope of -12dB per octave.

2-way speakers use 2 speakers on each channel and a crossover to divide the audio frequencies reproduced between the two. Each speaker receives a signal range it’s best suited for.

Illustrated diagram showing examples of 2 way home and car stereo speakers with 2 way crossovers

For example in 2-way speaker design:

  • Tweeters receive only high frequencies – typically around 3.5KHz and above
  • Woofers only receive lower frequencies – typically around 3.5KHz and below

The crossover frequency used varies by design needs, to there’s no “one” crossover frequency that works in all cases. Additionally, crossovers must be matched to the right impedance (Ohms rating) for the speakers they’re designed to work with.

The 2-way crossover evenly splits the incoming sound and sends it to the correct speaker such as the tweeter and a woofer.

Image of coaxial 2 way car speaker example

Coaxial speakers are 2-way speakers, too. In fact, in the example shown here, you can see crossovers on the rear of the speaker. Just like separate crossovers, lower frequencies are directed to the large woofer and highs are sent to the tweeter.

The result is that the sound produced is a full range of sound, but without distortion or poor performance you’d get when trying to play the same range in only 1 speaker. In other words, a 2-way speaker design can produce a clean, detailed sound.

In many systems, you won’t necessarily need expensive components or speakers to get great sound. Even low-cost 2-way speakers can sound very nice!

What is a good crossover frequency? What crossover frequency should I use?

The truth is, there’s no good set of crossover frequencies that work for every speaker. It depends on a lot of things.

However, here are some of the most common frequencies that work well in many cases. This is based on my experience with speaker design and many stereo installations.

Recommended crossover frequency table

Speaker/System TypeCrossover Freq. & TypeNotes
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.

Recommended reading

Product image of the Loudspeaker Design Cookbook by Vance Dickason

Want to learn a lot more and truly understand speakers, crossovers, and how to design a great sounding system of your own? Here’s the very book I learned a lot from myself.

You can pick up your own copy of the famous Loudspeaker Design Cookbook at Amazon today. It’s an excellent source of information including formulas you too can use to build your own car or home loudspeaker projects.

Interested in learning more about what tweeters do and the different kinds? Check out my wonderful guide to tweeters here.

For some great articles about crossovers, speakers, and lots of DIY projects, check out the Elliot Sound Products page.

Did I leave anything out? Drop a note!

I hope you’ve found my post helpful, clear, informative, and most of all what you were looking for. If you’ve still got questions, suggestions, or just want to say hi, leave a comment below or send me a message from my contact page.