What Is The Crossover Frequency Fc, Crossover Slopes, And Why Do They Matter?

What is the crossover frequency Fc featured image

Crossovers are extremely important to speaker systems and a big reason we’re able to get sound quality we love.

On the other hand, things like the crossover frequency (Fc), slopes (db per octave, and how it all works can be a little bit complicated if you don’t understand how it all works. I’d love to help!

In this article I’ll explain:

  • What the crossover frequency Fc is and why it’s important
  • What a crossover slope is and the most common you’ll come across
  • How to calculate dB crossover drop for frequencies including Fc
  • The role of inductors and capacitors (and “reactance” for Fc)
Contents

Crossover frequency Fc and crossover slopes explained

Crossovers and crossover frequencies explained diagram

This diagram shows examples of the 3 main filter types used in crossovers. Also shown are the most common crossover slopes which is the “steepness” of the filter (how effectively they block frequencies beyond the crossover frequency).

A crossover frequency, commonly written as Fc, is the audio frequency point in Hertz (Hz) at which the crossover delivers -3dB (1/2) power output to the speaker. Fc is the marking point after which sound frequencies will be greatly reduced to prevent them from reaching a speaker.

Past the crossover frequency (Fc) point the power output by the crossover will drop more and more, with less and less power sent to the speaker. As it so happens, at Fc the voltage output to the load (speaker) is 0.707 x the input voltage meaning you can calculate the decibel drop based on the voltage out versus the voltage in.

Why crossover frequencies are important

When designing speaker crossovers, the crossover frequency (fc) is used as a sort of line that marks where we want to start blocking the sound frequencies sent to a speaker. It’s usually based on the specifications provided by a speaker manufacturer that lists the sound frequencies a speaker can produce with good sound response and without distortion.

For example, tweeters can’t play bass notes from music and can even be damaged by them. Knowing that, we’d want to choose a crossover frequency high enough to block bass notes sent to tweeters to prevent distortion or damage. (Typically tweeters have crossover frequency in the thousands of Hertz [written as KiloHertz or kHz for short] like 3.5kHz, 5kHz, and so on – well above the range of bass & midrange sounds in music).

A crossover frequency is also sometimes called the corner frequency or cutoff frequency since we think in terms of how sounds are “cut off” after that point.

The crossover frequency Fc is very important for crossover design

Image showing speaker crossover examples and resistor, capacitor, and inductors

Speaker crossovers (also called “passive” as they don’t use electrical power to operate) use capacitors and inductors that are selected based on part values available and their cost. A crossover is designed based on a starting Fc frequency and adjusted as needed for the design goals.

Using the crossover frequency Fc as a starting point allows speaker system designers to calculate the part values needed (capacitors and inductors) depending on the speaker impedance. Since you can’t buy parts in just any value, the Fc we get based on what we want is a good starting point we can work with and adjust as needed to work with parts based on availability, price, and other factors.

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

Operational amplifiers, also called op-amps, are the most important building block for electronic crossovers. Electronic crossovers perform exactly the same job (and have the same basic behavior) as passive (speaker) crossovers. The difference is that they work on low-level signals before they’re amplified while passive crossovers work with amplified signals after the amp output.

NOTE: In this article while I describe how passive (non-electronic, non-powered) crossovers and Fc work, the principles are exactly the same for electronic filters.

Just like their larger passive capacitor or inductor-based counterparts, operational amplifier based crossovers have the same slopes and crossover frequency behavior. They simply do it with the signal before it’s amplified instead of after it.

How to calculate decibels (dB) for the crossover frequency Fc

How to calculate decibels for crossover frequency formula example

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 sounds you’d like to prevent reaching speakers, starting at the crossover frequency.

In the electrical engineering world, we traditionally use decibels (dB) when we talk about power measurements since they’re often non-linear. This just means that mathematically, power is often measured, charted, and tracked using exponential math such as logarithms (“10 to the power of x”, for example).

How crossover frequencies (Fc) and dB are related

Because crossovers reduce power at their output, it’s pretty common to measure the output reduction in decibels. One reason for this is that they have a gentle “slope” (downward curve) rather than a straight line if you were to see them graphed across the full range of audio frequencies.

For that and other reasons, we can measure the power output reduction in dB. To do so, you’ll need to know either (1) the power before and after the speaker/from the amp, or (2) the voltage at the speaker and from the amp.

Knowing those, you can easily calculate the dB output of a crossover with a scientific calculator on your computer or smartphone.

You can calculate dB for a crossover using these formulas: 

  1. For voltage: 20 x log(Vout / Vin ) = x dB
  2. For power: 10 x log (Power_out / Power_in) = x dB

Understanding crossover signal level in vs out and “negative gain”

Crossover Viin vs Vout diagram Fc frequency diagram

Crossover voltage out (called here “Vout”, the voltage to a speaker delivered from a crossover) can never be higher than the input – that’s not possible. Crossovers can only reduce the input directed to a speaker – they can’t amplify it. Some electronic crossovers do, but those intentionally have a gain on purpose and that’s not common in most cases.

For that reason, you’ll always get a negative dB answer if you do the math for the output of a crossover.

For the record, a negative dB value is used to show a reduction in engineering math while positive usually means a gain or increase in a signal. Amplifiers have a positive dB output (gain) while crossovers and some other components like resistors have a negative gain (a negative dB effect on a signal).

Attenuation is another way of describing a negative gain.

Note: the gain control of an amplifier is there to compensate for a high or low input signal level and is a separate section from the crossover circuitry.

How a crossover frequency Fc works: example diagram

Crossover frequency Fc explained example diagram

An example of a very common and simple high-pass crossover. A capacitor in series with a speaker will allow higher frequencies (above Fc) to pass with almost no volume or power drop to the speaker. It acts as a zero Ohm resistor (a short circuit wire) in series with it. However, for audio frequencies below Fc, the “resistance” (impedance, called capacitive reactance) of the capacitor will increase, allowing less and less voltage & power to reach the speaker. It will act like a very high-value resistor in series and therefore will block most of the signal from an amp sent to the speaker. In other words, a high-pass filter!

One of the problems I’ve found when we’re talking about this topic is picturing it in your mind. For example, it can be hard to understand what actually happens in real life when actually playing music in the real world vs just some explanation you’ve found on the internet.

All crossovers work the same – understand one, you understand them all (well, mostly!)

One important note I need to make is that the principles are the same regardless of the number of “orders”, or stages, a crossover has. For example, a simple 1st order crossover with a capacitor connected inline with a tweeter works on exactly the same principle as a fancier 2nd order 2-way crossover.

It’s just that the details are a little bit more complicated – not how it works. That part never changes.

There are some crossovers with more sophisticated features & designs I won’t get into here, but for the most part, the majority are all the same and do the same thing to varying degrees. The great thing is that once you understand the basics very well, you’ve got it figured out for the most part!

The fundamentals of how crossovers work with Fc

Image of a teacher demonstrating frequency crossover Fc explanation

The most important thing to know is that crossovers work by “absorbing”, or preventing, voltage and power from going to the speakers they’re connected to for the sound frequencies we don’t want them to play.

In the example from my diagram further above, you can see that:

  • Above the cutoff frequency Fc, a capacitor acts like an almost zero resistance connection – nothing is blocked and it acts almost like a straight section of wire.
  • When audio frequencies begin to reach Fc, the impedance of the crossover goes up, acting like a high-value resistor in series with the speaker. At Fc, the speaker receives only 1/2 the power it would otherwise (which also happens to be .707 times the input voltage from the amp or stereo).
  • The farther we go past the Fc limit, the crossover’s impedance is much bigger in Ohms; in fact, past a certain point, it will be several hundred Ohms typically. When that happens the speaker has about 0v and no power to it.

As you can see elsewhere in my article, the “steepness” of the drop in the power & signal level to the speaker depends on the crossover slope. A crossover’s slope is basically just a result of how many “stages”, or crossover sections, are used as needed for the particular speaker system or speakers we’re working with.

Crossovers like you see here and are always in increments of 6 decibels (dB) Per Octave:

  • 1st order crossover: a single capacitor or inductor is used, -6dB per octave reduction (not very steep).
  • 2nd order crossover: Two components sections are used: one capacitor, one inductor. –12dB/octave reduction (steeper, more effective, very popular).
  • 3rd order: two capacitors + 1 inductor or 2 inductors + 1 capacitor are used: –18dB/octave cutoff.

..and so on, with -12db being one of the most common crossover slopes you’ll find for both car audio crossovers and home audio speakers too.

An octave is just a half or double of an audio frequency. For example, 200Hz is an octave of 100Hz, 400Hz is one octave of 200Hz, then 800Hz, and so on. Equalizers and other audio electronics may use other variations with finer numbers like 1/3 octave, for example.

Crossover frequency formula math: inductive and capacitive reactance explained

Formulas for capacitive and inductive reactance explained

Shown here are the basic formulas for simple 1st order crossovers using capacitors and inductors. Capacitors have an impedance (Ohms) value that depends on the frequency just like inductors do.

Capacitors and inductors have a “resistance” called reactance (in Ohms just like resistance) that depends on the frequency. Here are a few basic things to understand:

  • Capacitive reactance increases as the frequency DECREASES. It’s normally written as “Xc.” Capacitance is marked in units of Farads, with most capacitors being values in the microFarad (uF) range, nanoFarad (nF), or even picoFarad (pF).
  • Inductive reactance INCREASES as the frequency increases. It’s normally written as “Xl.” Inductance is marked in units of Henries and typically found in units of microHenries (uH) or milliHenries (mH).
Note: “Micro” units are 1 x 10E-6 decimal places (ex. .000 001) while “nano” represents 1 x 10E-9 decimal places (ex. .000 000 001).

Again, it both cases, it’s just a form of impedance much like how a speaker voice coil that has a certain amount of inductance due to the coil of wire inside does. Both are measured in Ohms (Ω).

However, they complement each other and behave pretty much like the opposite of each other. For example:

  • Capacitors act like high-pass filters when connected in series and low pass filters in parallel.
  • Inductors act like low-pass filters when connected in series and high-pass-filters in parallel.

Example Ohms graph of the capacitive reactance for a series capacitor used as a crossover

This graph shows an example of a simple high pass capacitor using a 3.98 microFarad capacitor with an 8Ω speaker with a crossover frequency (Fc) of 5kHz. At the Fc value, the impedance is the same as the speaker load (8Ω) which means the speaker power has dropped to 1/2. Further below Fc the impedance grows higher and higher, blocking bass frequencies more and more.

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What Is A Good Crossover Frequency You Should Use For Home Or Car Audio?

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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How To Add A Resistor To A Speaker To Change Or Match Impedance

How to add a resistor to a speaker to change impedance featured image

Maybe you’ve got some extra speakers lying around or just want to know how to add a resistor to a speaker to change its impedance. Either way, you’re in luck!

In this article, I’ll show you:

  • How to change (or match) speaker impedances using resistors (with great diagrams to follow!)
  • The disadvantages of using resistors to change the speaker impedance
  • What kind of resistors you’ll need
  • What to do if you can’t find exactly the right resistors (there are some handy ways around that!)
  • Where to buy the right resistors – without going broke, too!
Contents

What kind of resistors should you use for changing speaker impedance?

Audio power resistor examples

Examples of common “power” (high-power) resistors used for audio & speaker impedance needs. These are resistors built to handle the higher power levels put out by an amplifier or stereo.

To work with the higher output of amps and receivers, you’ll need to use power resistors when working with speakers.

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 (not car amplifiers – those are higher power), you can often get away with around 10W to 15W.

Note: Resistance is usually described in units called Ohms, also commonly shown with the Greek omega “Ω” symbol.

Resistors to avoid

Example of standard electronic axial resistor

Shown here is an “axial” type resistor used for low-power electronics. These types of resistors aren’t suitable for working with speakers, audio, and other high power electrical circuits. Don’t use them for speakers as they can get extremely hot and potentially burn out.

While you might be tempted to try them, it’s important to avoid low-power (small) electronic resistors. These usually are rated for only about 1/8 of a watt to 1/2 watt. They’re simply too small to safely handle the large amount of heat that speakers and amps can dish out.

If you connect these to a high-power audio system they can become extremely hot, possibly causing burns or simply burn out altogether and cause failure (if you’re lucky) or even damage items they’re close to.

How to add a resistor to a speaker to change or match impedance

How to add resistor to speaker to change impedance diagram

You can change speaker impedance with resistors for two situations:

  1. To use a lower impedance speaker than you normally could with an amplifier or stereo.
  2. To use a higher impedance speaker where a lower one is needed (for example: speaker crossover designed only for a certain Ohm rating speaker).

Of the two cases, #2 is a lot less common. However, it’s really helpful when using speakers with crossovers and a few other situations you may run into.

If you’d like to use a higher speaker impedance than required for a stereo or amp, that’s normally not a problem (I’ll cover this in more detail later). I’ll explain 

1. Using resistors to increase the total speaker impedance load

As shown from my diagram above, if you’re planning on using a lower impedance speaker you can add resistors in series in order to bring up the total impedance that the stereo or amp sees. This allows you to safely avoid overheating and burning out the electronics you’re connecting to.

To do so:

  • Connect a resistor with the right resistance (Ohms) value to bring up the speaker impedance as needed, and with at least 1/2 the rated power of the stereo or amp’s power output rating. (Ex.: for a 50W/channel stereo, you’ll pick a power resistor with a rating of 25W or more)
  • Insulate any exposed resistor leads so they can’t short to speaker wire or metal. Always make sure the speaker or resistor wire is fully covered & not exposed.

A resistor connected in series simply adds its resistance to the speaker impedance rating. (Ex.: A 4 ohm resistor plus a 4 ohm speaker = 8 ohms total).

2. Using resistors to decrease the total speaker impedance load

What’s great is that not only can you increase speaker impedance connected to an amp or receiver, but you can also effectively decrease it, too! This isn’t something you’ll run across very often, but there are some situations where it’s really handy to know how to do it:

  • Matching a different impedance speaker to speaker crossovers
  • Temporarily using extra speakers until you can get replacements for the original ones
  • Replacing obsolete speakers with the next best ones you could find, but need to match the impedance
  • Making use of discounted speakers you’ve gotten an excellent price on

In this case, you can decrease the total speaker load seen by connecting resistors in parallel.

To do so, it’s basically the same as connecting resistors in series but the main difference is that you’ll wire it in parallel:

  • Calculate the resistor value you need, in Ohms (this is usually the same as the speaker: for example, to have a crossover see a 4Ω with an 8Ω speaker, you can connect an 8Ω resistor in parallel
  • Add resistor to speaker wire & speaker: Connect the resistor to the positive and negative terminals of the speaker (you can do this using speaker wire – there’s no need to do it right at the speaker if that’s a problem)
  • Insulate & fully cover any exposed speaker wire or resistor leads so they can’t cause a short-circuit to nearby wiring or metal

Resistance in parallel is a little bit more complicated

How to calculate resistance impedance in parallel example diagram

Resistance in parallel is a little bit more complicated to figure out as far as the math is concerned. However, don’t worry! It’s actually fairly easy once you understand how it all works.

Resistance in parallel adds using this formula: R_total = 1 / [ (1/R1) + (1/R2) ]

However, for resistance/impedance in parallel, if the values are all the same you can just divide by how many there are.

What are the drawbacks of using resistors for changing speaker impedance loads?

How power is divided between speakers and resistors diagram

Diagram showing an example of how power is divided up when using resistors to change speaker impedance seen by an amplifier or radio.

One thing to be aware of that it’s not a perfect solution – there are drawbacks.

One of these is that when you add a resistor in series with a speaker, the power delivered is split between the two. The second one is that you can’t get the same maximum volume from your amp or radio as you could using only the correctly matched speaker impedance.

For example, let’s say you want to use a 4 ohm speaker with an 8 ohm minimum 100W/channel home receiver. Adding a 4 ohm resistor in series will bring the total resistance (speaker load, in Ohms) up to the safe level of 8Ω.

However, having a series resistor connected to the speaker means that each one gets only 1/2 of the total power delivered. That means when using a resistor to compensate for the wrong speaker Ohms value, you’ll always lose some power across it. That’s regardless of connecting before or after the speaker – that doesn’t matter.

Overall power available is reduced for parallel resistors, also

Similarly, when using resistors in parallel with a speaker to bring down the impedance the amp or stereo sees, they share power as well. For example, using an 8Ω resistor in parallel with an 8Ω speaker will give 4 ohms total. However, with a 50 watt per channel amp, the power is still divided between them, leaving a maximum of 25W to the speaker.

That’s because they share the amount of electrical current the amp can produce. It’s no longer fully available for only a single resistance (a single speaker).

Using resistors can sometimes slightly affect the sound

Speakers aren’t exactly like resistors – this means in some areas their impedance changes with the sound frequencies they’re playing. This is due to inductance and how the voice coil is affected by an alternating current (AC) musical signal.

This being the case, adding a resistor can slightly alter the sound as it can cause a speaker to behave slightly differently across the range of sound. However, for the most part, this isn’t normally a big issue.

Just be aware that if you notice a difference that may be why.

What if you can’t find exactly the right resistors?

Example of power resistors in retail store on display hooks

Shopping for the right value & power rating of resistors can be a pain! That’s especially true when you can’t find the right values or if they’re out of stock

Here are a few tips for getting the right value resistors if you’re having problems finding what you need:

  • You can use multiple resistors that add up the right value.
  • They don’t have to be the perfect Ohms value – close is usually fine. For example, if you couldn’t find a 4Ω resistor, a 4.2Ω would be fine (as long as it’s ok for handling the power across it).
  • You can use two resistors in parallel to get a lower value: for example, if you need an 8Ω one, you can use two 16Ω resistors in parallel to get 8Ω.

In my experience, not every electronic parts store carries what you need. You may need to get creative if you can’t find what you want.

Some of the most common Ohm rating resistors are values like 1Ω, 2Ω, 5Ω, 10Ω, and so forth which you can use to get fairly close to the value you need.

Example of miscellaneous power resistors different values in package on floor

You can use multiple value power resistors with speakers to change their impedance. To do so, you can mix and match as needed to get the right overall value.

Where to buy resistors for changing speaker impedance load

Power resistors aren’t something you’ll find everywhere. A few places I’ve found them available are at:

  • Fry’s Electronics (may be going out of business, however, so be aware).
  • Parts Express – great supplier of many types of audio & speaker parts including resistors.
  • Amazon, eBay, and other online sellers of miscellaneous parts.

That’s if you’re the USA, of course. For other countries, you’ll need to search a bit if you don’t already have a good source.

How much do power resistors for use with speakers cost?

Power resistors should be affordable. For example, I’ve paid as little as $1.99 for a pair and often have gotten sets of 2 or 4 for about $5 or so. This is for resistors with up to 25 watts power handing, in fact.

More excellent articles to read

Check out these other articles I’ve put together! There’s a ton of great info just waiting for you.

There’s even more waiting, too! Check out all of my how-to & informational guides here.

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How Does Increasing Speaker Impedance Affect dB Volume & Power Output?

How does increasing speaker impedance affect dB output featured image

Does changing speaker impedance make a difference in the volume (decibels, or dB) you’ll get? And what about power – how does that change?

I’d love to help clear all of this up! In this article I’ll cover:

  • What impedance is all about
  • How the dB output (volume) changes if you increase speaker impedance
  • Car and home stereo power & volume differences related to speaker impedance

…and lots of other great info. Read on to learn more!

Contents

What is speaker impedance?

What is speaker impedance diagram

Speaker impedance, measured in Ohms, is the voice coil total resistance to the flow of electric current as it operates with a musical signal.

Any time you can a voltage delivering current flowing through wire you need some amount of resistance to limit how much can flow. Likewise, an amp or stereo needs at least some speaker resistance (a speaker load, if you will) to limit how much electrical current the radio or amp tries to supply.

Unlike straight wire that goes from point “a” to point “b” 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 has resistance depending on the frequency of the alternating current (AC) flowing in it.

This is called inductive reactance.

Speaker impedance changes with music frequencies – somewhat

For car speakers, this means that the real impedance (the total resistance) actually changes a little bit as music plays! However, the good news is that we can still give speakers an Ohms rating (speaker impedance rating) as it’s always within a certain range like 2 ohms, 4 ohms, and so on.

When we talk about the impedance of a speaker, most of the time people are referring to the category (general range) of the speaker as used to match home or car stereo amplifiers.

In the electrical world, Ohms are sometimes represented by the Greek symbol Omega, or “Ω.”

How does speaker impedance work?

how does speaker impedance work diagram

As I mentioned earlier, a speaker’s impedance is made up of it’s resistance and inductive reactance due to the coil of wire that makes up the voice coil.

Impedance can’t be measured fully with a direct current (DC) test meter. For example:

  • If you use a digital multimeter set to read resistance in Ohms, you’ll measure only the DC resistance of the wire.
  • If you had the right equipment and could apply an AC signal you’d see an additional amount of resistance also.

Adding both of these together would give the actual “impedance” total. Like wise, the same things happen when an musical signal is driving a speaker to make sound: the amp or stereo will “see” a speaker load that’s the sum of both.

Resistance and inductive reactance math explained

Unlike standard resistance, you can’t simply add inductive reactance to it. To compute the total speaker impedance, you’d add them together by finding the square root of the sum of the squares, sometimes called the “trigonometric sum.”

Note: For the sake up general discussion, we don’t need to know the exact speaker impedance when matching speakers, talking about dB output & power, and so on.

I’m offering this as additional info to help your understanding of where it all comes from.

How does increasing speaker impedance affect power? 

Speaker impedance vs power & Ohms law diagram

As you can see from the diagram I’ve provided above, increasing a speaker’s impedance doesn’t just affect volume (which I’ll cover in more detail below) but power, too. In fact, it can make a big difference in how much power you’ve got on tap with your home or car stereo or amplifier.

That’s because of Ohm’s Law and how power works:

  • Home & car stereos and amps have a certain amount of voltage they can produce to deliver power to speakers.
  • According to Ohm’s Law, if you change the resistance (speaker impedance, in this case), the power developed changes accordingly.
  • Amps and radios have an upper limit to how much voltage they can put out, so the maximum output doesn’t change if you increase the speaker impedance. It’s a fixed limit.
  • Therefore: if you increase a speaker’s impedance, less power will be developed using the same stereo or amp.

Increasing speaker impedance vs power in watts comparison graph

In this example graph, you can see how much power a 4 ohm speaker will develop with the same amplifier as an 8 ohm speaker. The 4 ohm will not only develop 2x the power of the 8 ohm speaker, but the 8 ohm one will never get the full power available from the amp.

That’s important in some cases and less important in others. For example, for home stereos where you don’t need a huge amount of power, you can use 16 ohm speakers in place of 8 ohm ones without noticing that much of a difference.

However, it’s a different case when we talk about car audio as they often need a lot more power to produce great sound or volume in a vehicle – especially with subwoofers for heavy bass. In that case, switching from 4 ohm to 8 ohm speakers means you’ll have 1/2 the power available that you used to.

That’s a big difference!

Does speaker impedance affect volume? 

Increasing speaker impedance vs dB volume output comparison graph

Diagram showing an example graph comparing the dB output volume of an 8 ohm speaker at the same level as a 4 ohm speaker. A 4 ohm speaker will produce a few more decibels of volume at a lower output level of a radio or amp. When the amp is at its maximum output (maximum output voltage), the 4 ohm speaker will have a much higher dB output than the 8 ohm at the same level.

In the graph above, you can see what happens when we use an 8 ohm speaker in the place of a 4 ohm speaker connected to the same amplifier. It might seem confusing at first, but what the graph is showing is:

  • The dB output of the 4 ohm speaker at its 1 watt output and higher. [This is a lower output voltage on the radio or amp than for an 8 ohm speaker]
  • The dB output for an 8 ohm speaker at those same amp levels.
What this helps show is that when you increase the speaker impedance on a stereo or amplifier designed for a lower speaker impedance, the decibel output (dB, volume) will be lower throughout the full power range.

It can also be a lot less than the correct impedance at the maximum output.

You’ll have to increase the output of the radio or amp to get the same dB volume output for the higher impedance speaker.

This means that:

  • For a higher impedance speaker, the overall volume will be a few dB lower typically, depending on the particulars of that speaker.
  • You’ll never get the full capacity out of the stereo or amplifier as you would with a lower impedance speaker like it’s designed for.

For car subwoofers, for example, that’s a big deal. For every doubling of power to a speaker, you’ll get 3dB more volume, not double the volume. 4x the power is 6dB, and so on.

Our ears work in a way such that about 10dB is considered a big difference, which takes about 10x the power. When doubling the speaker impedance, as you can see from the graphs above, you’ll “run out of steam” well before reaching the maximum power your amp could put out like it would with the correct (lower) impedance speaker.

For home or car stereos with lower power output (most car stereos are limited to about 14-15W or so) that’s quite a difference.

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

Crossover shift due to speaker impedance change explained diagram

What is crossover shift?

Speaker crossovers are designed using predetermined values for the capacitors and inductors they use as filters. When a speaker manufacturer design speaker crossovers, it’s always based on the speaker impedance they’re designed to be used with.

Crossovers behave differently when the speaker load (Ohms load they see) changes. Because of this, when you change the speaker impedance you change the crossover frequency and the sound. The crossover frequency will change – typically a lot.

In other words, changing the speaker impedance will shift the crossover frequency. 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 should only be used with the speaker impedance they’re designed for or they won’t sound right.

For example, using a 16 ohm speaker with an 8 Ohm home speaker crossover won’t work correctly. It’ll sound poor and won’t work as designed. You can definitely expect to be disappointed with the sound.

Don’t forget that if your speakers aren’t of the same impedance, the higher one won’t be at the same output level as the correct one, meaning they’re not properly matched.

Do I need to match tweeter and woofer impedances for 2-way speakers?

Do I need to match speaker impedance in 2-way systems? Image man thinking

I don’t recommend mixing speaker impedances in 2-way or 3-way speakers because they won’t have the same volume level once you turn up the volume. That means the sound won’t be right and you’ll be left having to deal with some sound frequencies being poor after a certain point.

As you can see from the graphs I provided earlier, as the power increases the higher impedance speaker will always fall short of the also correctly matched speaker.

In 2-way speaker systems, that an even bigger problem because very often tweeters already have a higher volume output than their woofer or midrange counterparts. To make matters worse, most 2-way speakers have at least crossover they depend on.

This means in many cases changing the speaker Ohm load will also change the crossover behavior and affect the sound negatively.

I’ve seen some speakers systems where one speaker (typically the tweeter) has a different Ohms rating than the others, but in that case the designers take that into account.

More great speaker articles

There’s lots more to learn!  Check out my other great articles you’ll love:

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What Will A 2, 4, or 8 Ohm Impedance Speaker Measure For DC Resistance?

What will a 2 4 8 ohm impedance speaker measure DC resistance featured image

Speakers a little bit of a curious thing: they’re called 4 or 8 ohm impedance and so on, but most don’t actually measure that amount of resistance in Ohms when you check them!

Why is that, and what should you measure when checking the DC resistance for most speaker impedances ( 2, 4, and 8 ohm)?

I’ll explain everything in detail and provide a handy chart of some DC measurements you can expect.

Contents

What will a 2, 4, or 8 Ohm impedance speaker measure for DC resistance?

Speaker impedance label and ohm meter examples

In the real world an 8 ohm speaker will have a resistance measurement less than its 8 ohm rating. That’s normal and is because the DC resistance and the total resistance, called the impedance, are not the same. DC resistance is always less than the total speaker impedance as you’ll see later.

You can find the typical DC Ohms measurement range for many speaker common speaker impedances here. To use this chart, just find the impedance rating you’re interested in (1st column) and look at the Ohms measurement range in the 2nd column.

Speaker impedance DC resistance/Ohms range chart

Speaker impedanceDC resistance
2 ohms1.2-2 ohms
4 ohm3.1-4.0 ohms
8 ohm5.7-8 ohms
6 ohms4.0-6 ohms
1 ohm*0.5-1.0 ohms
16 ohms*12-16 ohms

*(1 ohm speakers are unusual but can be found in some car stereo products such as Bose premium amplified systems. 16 ohm speakers may sometimes be used for home or other speaker systems but you won’t run across them very often, either.)

The speaker DC resistance chart listed here covers a wide range of speakers. These can vary quite a bit between different models and different sizes of speakers, even from the same manufacturer. Don’t be surprised if your 8 ohm home speaker measures around 6 ohms for example.

What is speaker impedance? Impedance vs resistance explained

What is speaker impedance diagram

A speaker’s impedance is the total resistance to the flow of electrical current when it’s connected to an amplifier or stereo. It’s a combination of the direct current (DC) resistance AND the portion of resistance due to magnetic fields created when an alternating current (AC) musical signal is applied.

Both resistance and impedance are measured in Ohms so the end result is a total value in Ohms also.

For example, when measuring a speaker’s resistance with a test meter or Ohm meter, the meter puts out DC voltage and measures DC resistance. If you had some fancier test equipment and a lab to put out an AC signal, you’d also see that a speaker develops more resistance based on the frequency applied to it.

Speaker impedance, measured in Ohms, is the voice coil’s total resistance to the flow of electric current as it operates with a musical signal, not just the DC resistance of the wire it’s made of.

Speaker impedance vs resistance explained

how does speaker impedance work diagram

As I mentioned, speakers use a voice coil that’s a long length of wire spun into a tightly wound coil by high-precision machines at the speaker factory.

When you play music and drive a speaker with power, magnetic fields are created as current flows through the coil. These fields create an opposition (resistance, called reactance in this case) to the current flowing through it. This is a very common property of wire coils and is also used to create electric motors, spark plug coils for engines, stun guns, and much more.

The coil has a property called inductance that affects how strong the magnetic fields are. Inductive reactance is different from resistance as it changes as the frequency changes, unlike DC resistance.

This kind of “resistance” is called inductive reactance.

Resistance measurements (Ohms) are sometimes shown by using the Greek symbol Omega: “Ω”

Where the total speaker impedance comes from

How to calculate speaker impedance diagram

The mathematical formulas for calculating speaker voice coil inductive reactance at a given frequency and total speaker impedance. It’s a bit complicated, but not too bad once you understand it!

Unfortunately, impedance/inductive reactance is a bit complicated to deal with mathematically. Because of how inductance works and the physics involved, the total speaker impedance (resistance + inductive reactance) isn’t as simple as just adding together the resistance and the inductive reactance.

Instead, speaker impedance is found from the square root of the sum of the squares of the coil’s wire resistance and the inductive reactance.

Inductive reactance is represented as “Xl”, pronounced “X sub L” and is measured in Ohms just like resistance. Inductance is measured using a unit called the “Henrie” and is shown as an “H.” “uH” means microHenries (1/100,000 of a Henrie), mH” represents milliHendries (1/1,000) of a Henrie), and so on.

Inductors are extremely useful for audio – especially for speaker crossovers. In that case, they’re a critical component for high- or low-pass crossovers and are chosen based on their inductance.

How to measure speaker impedance with a test meter correctly

How to measure speaker impedance with an Ohm meter example

In this picture, you can see an example of how to measure speaker impedance using an Ohm meter or any standard test meter set to measure resistance in Ohms. To do so, set it to one of the lowest ranges (0-10 Ohms, 0-20 Ohms, etc) or the auto-range setting if available. Touch the test probe leads firmly against clean, bare metal on the speaker terminals with at least one speaker wire removed to avoid a false measurement.

To measure the impedance of a speaker you’ll need a multimeter or a dedicated resistance meter.

Do the following:

  1. Switch on the meter and set it to measure Ohms on the lowest range. This is often the x1 range, 0-10 Ohms, 0-20 Ohms, or auto-range setting.
  2. IMPORTANT!Disconnect one or both speaker wires from the speaker to avoid a false reading due to other resistance that may be connected to it. If other things are connected they can cause false readings and give you the wrong idea.
  3. Hold the probes firmly against the speaker terminals on a clean, bare metal spot. The meter should quickly settle to a reading. The meter will show the DC resistance of the voice coil wire.
  4. Use the measured value to determine the closest approximate speaker impedance (see my chart above if you like)
  5. For speakers inside a cabinet or enclosure such 2-way speakers, crossovers may be in use and these can interfere with this reading with a few exceptions. However, in many cases, you still measure the resistance of a woofer fairly well. (I still recommend disconnecting at least one wire before taking a measurement.)

Remember that you won’t measure exactly 4 ohms for a 4 ohm speaker or 8 ohms for an 8 ohm speaker, for example. The DC measurement is almost always 30% lower than the impedance rating on the speaker’s package or label.

Selecting the correct test meter resistance (Ohm) range for speakers

Image showing examples of test meter resistance setting for measuring speaker impedance

It’s important to use the correct Ohms range on your meter when measuring speaker impedance. That’s because the wrong setting may display nothing useful or mistakenly give you the idea that the speaker is blown or even an incorrect reading.

If you’re not sure, check the test meter’s manual. Many modern digital meters often have an auto setting that will automatically adjust for the Ohm measurement it detects and will change the range and decimal place automatically for you. Other meters require you to select the correct range manually.

As a general rule, use the lowest range that includes 0-10 ohms (or similar) then go up if necessary.

That should almost never happen, but in the case of a poor connection, a blown (or almost blown) speaker, stuff can happen and you could get a reading that’s not really the speaker’s normal DC resistance.

In my experience, however, that’s not something you’ll run across often, if at all.

What happens if my speaker impedance is too low or too high?

4 ohm vs 8 ohm speaker power comparison graph

This is a graph showing how a higher impedance speaker makes less power than the correct speaker that should match an amp or stereo. For example, using an 8 ohm speaker in the place of a 4 ohm one means you’ll get 1/2 the power and as a result, you’ll never be able to the same volume or performance that you paid for with your system.

Using a speaker that’s not matched to the stereo or amplifier it’s rated for can have relatively minor – or even terrible results depending on what you’re dealing with:

  • Using a higher impedance speaker won’t damage equipment. The result will be lower power developed and therefore lower possible volume. You may also introduce problems with speaker crossovers, however.
  • Using a lower than specified impedance speaker will cause radios or amps to suffer extreme heat and even permanent damage because the current output will be much more than what it’s designed for.

As an example, if you were to use 8 ohm speakers in the place of 4 ohm car stereo speakers you wouldn’t hurt anything because less current will be output and it wouldn’t overheat. The problem will be (although it will play fine, otherwise) is that the total power available will be 1/2 that of a 4 ohm speaker.

What happens if using a higher or lower speaker impedance diagram

However, there’s a huge problem if you use a lower impedance speaker that’s matched to the amp, home stereo, or etc. The end result will be that it’ll being to overheat and can potentially suffer permanent damage and stop producing sound.

That’s because using a lower speaker impedance causes the radio or amp to attempt to put out twice as much (or more!) current than it’s designed for.

If you’re lucky the radio, home stereo, or amplifier will shut off to protect itself. Unfortunately over the years more often than not I’ve seen amps or radios burn out their output stages because of a short-circuit or the wrong impedance speakers being connected.

Why do lower impedance speakers cause an amp or radio to burn out?

The high-power transistors used in home or car audio devices can only handle a certain amount of electrical current (amps) or heat. When forced to handle more than their safe limit they become incredibly hot and start to break down. Before long they’ll stop working altogether as the semiconductor components are destroyed.

Caution! Never wire speakers in a way that gives a total speaker load lower than the radio or amp is rated for. Also, don’t guess about the correct speaker impedance – check first. Don’t risk it as it’ll be an expensive lesson it what not to do!

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.

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!

More excellent articles to help

Check it out – there’s lots more great reading where this came from!

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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 begin to “break up” at a lower volume than they used to.
  • 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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Why Is It Bad If Speaker Impedance Is Too Low? Your Question Answered

Why is it bad if speaker impedance is too low featured image

It can be confusing when we talk about impedance, Ohms, and all that with regards to car or home audio speakers. Yeah, most people are familiar with speakers, Ohm ratings and more…but what does it really mean?

Exactly why is it bad if speaker impedance is too low? That’s what I’ll answer here and clear up once and for all.

In this article, I’ll cover everything you need to know:

  • What exactly is speaker impedance?
  • Two big reasons why a low speaker impedance can be bad…and why it matters
  • Why you can use higher impedance speakers but not lower ones (and what to expect)

There’s a lot to cover so let’s jump right in!

Contents

What does impedance mean for speakers? Speaker Ohms explained

Illustrated diagram of a woofer speaker and its parts (3D exploded view)

An illustrated view of the parts that make up a speaker including the voice coil. The voice coil is a tightly-wound, long length of wire that has a certain amount of resistance from the electrical conductor used. It creates magnetic fields that drive the speaker cone forward and back, creating sound as it moves air.

In the world of electricity and electronics, we need a few things to do useful work:

  • A power source with voltage to move electrical current through a resistor, motor, etc to do something useful. A home or car amplifier or radio provides this.
  • Electrical conductors (speaker wire) to create a path for that current to flow
  • Some level of resistance to limit how much current can flow (too much current causes things to burn out, get hot, etc)

By that same token, just like other electrical devices, speakers are like little motors that use electricity flowing to turn motion (the cone) into sound we can here – that’s basically all speakers are!

What does speaker impedance mean?

What is speaker impedance diagram

Speaker impedance, measured in units of resistance called Ohms, is the total amount of resistance a speaker has to the flow of electricity. 

Speaker impedance comes from two things:

  1. The resistance of the long winding of wire that makes up the voice coil
  2. A special property created when wire is wound into a coil called inductance

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

Speaker voice coils use a very long length of wire that’s tightly wound into the voice coil necessary to produce magnetic fields to create motion of the cone. Because of this length, there’s always a certain amount of resistance that is part of what makes up speaker impedance.

The resistance of a given speaker is almost always a few units of resistance, measured in Ohms.

What does inductance mean? Why it matters in speakers

Example of an inductor

Inductors are very useful electrical parts that take advantage of inductance. Inductance is a property of electrons flowing through a wire loop and the magnetic fields that build up because of it. Similarly, speakers have inductance due to their voice coils, although a small amount.

Coils of wire have an interesting side effect that happens unlike straight sections of wire. The voice coil’s wire winding forms a loop that has an electrical property called inductance.

Inductance is different from resistance as it changes as the frequency changes; resistance stays the same. This is called inductive reactance, which is just a more complicated resistance to the flow of electrical current.

For speakers, this matters because it means that the total resistance is made up of the two things I mentioned: wire resistance and inductive reactance. The name used to describe this total is impedance.

For speakers, this means that impedance (the total resistance) changes slightly as music plays because of the changing sound frequencies. However, the good news is that we can still categorize speakers according to an Ohms rating since it’s always pretty close.

When we talk about the impedance of a speaker, most of the time people are referring to the range of the speaker assigned to categories like 2 ohms, 4 ohms, 8 ohms, and so on. This is how we match speakers to a car or home amplifier, radio, and so on.

In the electrical world, resistance units measured in Ohms can be written as the Greek symbol Omega, or “Ω.”

How does speaker impedance work?

how does speaker impedance work diagram

When a musical signal (made up of alternating current) is applied to a speaker it generates magnetic fields as current flows through the tightly wound wire coil. Interestingly enough, a coil of wire develops magnetic fields that resist the flow of the current (resistance, also called reactance in this case).

Similarly, many other electrical components like motors deal with the same electrical resistance as alternating current (AC) is applied.

How the math works (yeah, it’s a little complicated!)

How to calculate speaker impedance diagram

Because of how inductance works and the physics involved, the speaker “impedance” (total resistance) isn’t the sum of the resistance and the inductive reactance. Instead it’s the “algebraic” sum, meaning it’s the square root of the sum of the squares. You may remember this kind of math from trigonometry class.

Speaker impedance isn’t as simple as just adding the measured DC resistance of the coil wire and the inductive reactance for a given frequency.

Instead, speaker impedance is found from the algebraic sum of the coil’s wire resistance and inductive reactance. You can find this by squaring each and then taking the square root of the two numbers added together.

Inductive reactance is commonly written as “Xl”, pronounced “X sub L” and is measured in units of Ohms just like resistance. Inductance is measured using a unit called the “Henrie” and commonly noted with an “H”: “uH” for microHenries, “mH” for milliHendries, and so on.

There’s also a corresponding value for capacitors called capacitive reactance (Xc) but that doesn’t usually apply for speaker voice coils. It’s very important for speaker crossovers, however.

Why is it bad if speaker impedance is too low?

What happens if using a higher or lower speaker impedance diagram

Just like any other device connected to an electrical power source, the speaker impedance will determine how much or how little current a home or car receiver, amplifier, etc will produce. The speaker impedance also affects how some speaker components such as speaker crossovers behave too.

What happens if speaker impedance is too low?

You can connect a higher speaker impedance in most cases without any problems (at least not major ones). A radio, home or car amplifier, etc will still produce sound and run at normal or low temperatures. That’s because a speaker with a higher impedance than expected will reduce how much electrical current the audio source tries to produce.

As a side effect, you’ll get sound but with much lower power output than you would with the correct speaker load. Car stereos or amps, for example, have to work with lower voltages than home stereos so they need a lower impedance 4 ohm speaker typically to produce more power.

Home stereos, on the other hand, have higher voltage available and can use a higher speaker impedance (8 ohms, typically).

Illustrated image of Rockville marine audio amplifier guts & internal view

Internal view of an amplifier. When connected to a speaker impedance load that’s too low, the amp will begin to get very hot and this can burn out the output transistors as they can’t handle the heat caused by trying to supply excessive current to a lower speaker load.

However, using a lower speaker impedance is bad because it causes the radio or amp to attempt to put out twice as much (or more!) current than it’s designed for. Your home or car stereo will get very hot quickly and if you’re lucky will go into a self-protect mode and shut itself off.

However, in my experience, it’s pretty common for the output stage electronics to burn out when connected to a lower speaker load than they should be. The high-power transistors in a home or car amplifier or stereo are only rated for a certain amount of heat & electrical current.

When they’re forced to try and handle an amount outside that range they become super hot and start to break down permanently. It doesn’t take long before the damage is permanent and they no longer produce sound.

Caution! Never wire speakers in a way that gives a total speaker load lower than the radio or amp is rated for. Also, don’t guess about the correct speaker impedance – check first.

I’ve seen cases where someone’s “friend who’s smart” has as a way to “get more power” but caused a stereo or amp to try to and put out more power than it was designed for. The end result was a burned-out amplifier.

Why does speaker impedance matter for crossovers?

Examples of 2 way crossovers and diagram

Speaker crossovers work to separate the sound sent to certain speakers for improved sound, reducing distortion, and to give you more control over how they’re used. For example, they block bass that tweeters can’t produce and highs that a woofer can’t produce well. However, they’re designed for a specific speaker impedance. Changing the speaker impedance affects the sound.

Speaker crossovers are amazingly helpful for getting better sound with speakers. Even the cheapest, most basic capacitor connected inline with a tweeter working as a high-pass filter makes a big difference in the sound.

The result is cleaner sound and avoiding possibly damaging it when bass sounds are played.

The catch is that because of how crossover components (capacitors and inductors) behave, they’re designed for specific speaker loads and can’t be used with other Ohm loads without affecting the sound output.

Crossover shift when using different impedance speakers

Crossover shift due to speaker impedance change explained diagram

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 frequency
  • Doubling the  speaker impedance (ex: 8 ohms to 16 ohms) halves the frequency

That’s bad because it allows the speakers to be sent a sound range they’re not suited for. In the case of tweeters, bass & midrange are bad because they can’t produce it properly. Similarly, many woofers can’t produce high frequency sounds well.

The end result in either case is poor sound that’s a lot worse sounding that it should be. If you change the speaker Ohms load you’ll have to replace the speaker crossover as you’ll need different parts values for it to work the same.

Is 8 or 4 ohm better? Is higher or lower impedance better for speakers?

What is better 4 ohm 2 ohm 8 ohm speakers

8, 4, and 2 ohm speakers aren’t necessarily “better” than one another. The correct answer is that it depends on the application and what stereo or amplifier is being used. The best impedance is the one that matches an amplifier or stereo’s impedance spec correctly.

By industry tradition, 8 ohms are used for home and some theater speakers. 4 ohm speakers are generally used for car and marine audio, with some 2 ohm models also (usually subwoofers).

For example:

  • 8 ohm speakers are used in home stereo systems and require 1/2 the current of a 4 ohm speaker. That means they can use smaller speaker wire as they can take advantage of home electrical systems that have a high voltage supply for driving speaker amplifiers.
  • 4 ohm speakers are used because car stereos and amplifiers (particularly car head units) can’t make large amounts of power in speakers as they have a very low 12V power supply. Reducing the speaker impedance from 8 to 4 means we can double the power for the same output voltage.

As a matter of fact, car stereos can only put out about a small 15-18 watts RMS per channel, despite the exaggerated peak power ratings you may see in advertisements. That’s because they only have about 12 volts to work with and have to divide that in half in order to produce AC waves that drive a speaker.

Car amplifiers are able to deliver huge amounts of power to 4 and 2 ohm speakers. They use an internal “inverter” power supply that steps up the +12V supply to higher voltages. This way they’re able to supply much more power to 2 or 4 ohm speakers than would be possible otherwise.

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What Is Car Speaker Impedance? Speaker Impedance And Ohms Explained

What is car speaker impedance featured image

Impedance is kind of a “scientific” sounding word, right? At first glance it’s fairly confusing and you might not know how much – if at all – it matters for hooking up speakers.

But what is car speaker impedance? As it turns out, it’s really important and can have some serious consequences on your vehicle’s sound, your car amplifier, and more. Let’s dig in!

Contents

What does speaker impedance mean?

What is speaker impedance diagram

Speaker impedance, measured in Ohms, is the voice coil total resistance to the flow of electric current as it operates with a musical signal.

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 straight wire that goes from point “a” to point “b” 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. This is called inductive reactance.

For car speakers, this means that the real impedance (the total resistance) actually changes a little bit as music plays! However, the good news is that we can still categorize car speakers according to an Ohms rating since it’s always pretty close.

When we talk about the impedance of a speaker, most of the time people are referring to the category (general range) of the speaker as used to match home or car stereo amplifiers.

In the electrical world, Ohms are sometimes represented by the Greek symbol Omega, or “Ω.”

How does speaker impedance work?

how does speaker impedance work diagram

When a musical signal (made up of alternating current) is applied to a speaker it generates magnetic fields as current flows through the tightly wound wire coil. Interestingly enough, a coil of wire develops magnetic fields that resist the flow of the current (resistance, also called reactance in this case).

Similarly, many other electrical components like motors deal with the same electrical resistance as alternating current (AC) is applied.

How to calculate the total impedance (if you like!)

How to calculate speaker impedance diagram

Because of how inductance works and the physics involved, the speaker “impedance” (total resistance) isn’t the sum of the resistance and the inductive reactance. Instead it’s the “algebraic” sum, meaning it’s the square root of the sum of the squares. You may remember this kind of math from trigonometry class.

Speaker impedance isn’t as simple as just adding the measured DC resistance of the coil wire and the inductive reactance for a given frequency.

Instead, speaker impedance is found from the algebraic sum of the coil’s wire resistance and inductive reactance. You can find this by squaring each and then taking the square root of the two numbers added together.

Inductive reactance is commonly written as “Xl”, pronounced “X sub L” and is measured in units of Ohms just like resistance. Inductance is measured using a unit called the “Henrie” and commonly noted with an “H”: “uH” for microHenries, “mH” for milliHendries, and so on.

There’s also a corresponding value for capacitors called capacitive reactance (Xc) but that doesn’t usually apply for speaker voice coils.

How to tell the impedance of a car speaker

Car speaker impedance example

There are a few different ways to tell what a car speaker’s impedance is – even if it’s missing the label or it’s not printed on it anywhere.

Here’s what you need to know:

  • A speaker’s impedance is usually listed on the speaker magnet, packaging, and/or box and specifications. Unfortunately, it’s not always the case as some manufacturers might not have printed it on the speaker.
  • If the Ohm rating (impedance) is not available on the speaker, you can measure the impedance of a speaker using a test meter set to the Ohms (resistance) function. This will give the resistance of the voice coil which will let you determine the speaker’s impedance range/category such as 2 ohms, 4 ohms, 8 ohms, etc.
  • Unlike when a speaker is playing, measuring resistance with test meter won’t give you the total impedance – just the DC resistance of the speaker coil. However, that’s all you need to figure out the Ohms rating of your car speaker.

Long story short, if your speaker doesn’t have the impedance listed anywhere or you can’t find the manufacturer’s specs, the best thing to do is to measure it.

That’s the best way as you can be 100% sure of what you’re dealing with – especially if you need to match the impedance to an amplifier, car stereo, or crossover.

How to measure the impedance of a car speaker

How to measure speaker impedance with an Ohm meter example

It’s easy to measure car speaker impedance using a test meter set to read resistance (Ohms). Once you get a reading you can tell what Ohms rating your speaker is.

To measure the impedance of a car speaker you’ll need a multimeter (test meter with multiple functions) or a dedicated Ohm (resistance) meter. Digital multimeters are inexpensive and easy to find these days so I recommend using one of those.

  1. Turn on the meter and set it to measure resistance (Ohms) on the lowest range. This is usually the x1 range, 0-10, 0-20, or auto range setting.
  2. Disconnect one or both speaker wires from the speaker to avoid a false reading due to other resistance that may be connected to it.
  3. Hold the probes tightly against the speaker terminals on a clean, bare metal spot. The meter should quickly settle to a reading. The meter will show the resistance of the voice coil inside the speaker.
  4. Use the meter reading to determine the closest approximate speaker impedance (see my chart below for help).
  5. For speakers inside a box or enclosure there may be a crossover connected elsewhere which can interfere with your reading, so be sure to disconnect at least one speaker wire if possible. Subwoofers are usually fine to measure while installed in a subwoofer box.

As I mentioned above, the goal here isn’t to try and measure the perfect impedance rating.

Remember that you won’t measure exactly 4 ohms, 8 ohms, etc. You’ll measure an Ohms value that’s close to that and will help you tell the actual Ohms/impedance range of your speaker.

Note: Speakers like tweeters with a capacitor  crossover connected to them will act as an open circuit and will interfere with your measurement.

See my notes below on how to deal with that.

How to set your test meter for measuring car speakers

Image showing examples of test meter resistance setting for measuring speaker impedance

Shown are some example test meter resistance range settings to use for typical test meters.

As I mentioned earlier, it’s important to use the correct resistance range on your meter when measuring speaker impedance. that’s because the wrong setting may display nothing or give you the wrong idea that perhaps the speaker is blown when it isn’t.

If you’re not sure, check the test meter’s manual. Many modern digital meters often have an auto setting that will automatically adjust for the Ohm measurement it detects and will display the reading & decimal places accordingly. Other meters require you to select the correct range manually.

As a general rule, use the lowest range that includes 0-10 ohms (or similar).

Once you’ve got your measurement, use my speaker impedance chart to find the next closest speaker impedance value listed.

Measuring speaker impedance for tweeters & after crossovers

Diagram showing where to measure speaker impedance of tweeters with crossover

Tweeters often are supplied with a high-pass crossover in the form of a capacitor. To get a correct reading you’ll need to disconnect it or measure around it. Be sure to disconnect the tweeter from an amp or head unit!

Measuring the speaker impedance where crossovers are in place is a problem. That’s because capacitors, which are commonly on tweeters as a high-pass filter, appear to behave like an open circuit when measuring resistance as the capacitor charges.

You’ll want to measure around the capacitor if used or disconnect one capacitor lead or one tweeter wire. 

For 2-way speakers, there may or may not be a crossover used on the woofer. Often there’s an inductor in series with it. The good news is that directly reading resistance across a speaker and an inductor doesn’t make much difference – inductors have a tiny resistance value.

In fact, they’re usually in milliOhms (thousandths of an Ohm) which is almost nothing. However, as a general rule, it’s best to disconnect speakers from their crossovers before measuring Ohms.

Car speaker measured Ohms to impedance chart

Measured Ohms*Speaker impedance rating
3.1-4.0 ohms4 ohm
6.0-8 ohms8 ohm
1.2-2 ohms2 ohms
4.0-6 ohms6 ohms
0.5-1.0 ohms1 ohm**
12-16 ohms16 ohms**

To use this chart, take the speaker resistance measurement you got from your test meter reading and use it to compare to the measurements here. Your car speaker should fall into one of the common ranges you see above.

*This is an approximate range and should cover nearly all speakers but may vary slightly.

**1 ohm is rare but can be found in some car stereo products such as Bose premium amplified systems. 16 ohm speakers may sometimes be used for home or guitar amp systems, but aren’t very common.

Can I hook up 8 ohm speakers to a 4 ohm amplifier or radio?

4 ohm vs 8 ohm speaker power comparison graph

This graph shows what happens when you use an 8 ohm speaker in the place of a 4 ohm one. The 8 ohm speaker will work – however, it comes with a price. Since the 8 ohm speaker isn’t matched to the 4 ohm amp, it can only receive up to 1/2 the power output (and a lower volume) than a 4 ohm speaker would.

Using a speaker that’s not properly matched to an amplifier or car stereo can have minor – or major – consequences. 

Using an 8 ohm speaker in place of a 4 ohm won’t hurt anything. However, it can only develop 1/2 the power output of a 4 ohm speaker meaning lower volume. It also won’t work properly with speaker crossovers since it will shift the cutoff frequency.

For example, if you were to use some home stereo 8 ohm speakers or subwoofer instead of 4 ohm speakers, you’d notice the volume would be lower than when using 4 ohm ones. That’s because a speaker needs more and more power output to increase the volume more and more.

Car amplifiers & car head units don’t have much supply voltage to work with unlike home stereo receivers and amps. That means they need a lower impedance speaker to develop the same amount of power by letting more current flow.

I also don’t recommend mixing 8 and 4 ohm car speakers because they won’t have the same volume level once you turn up the volume. That means the sound won’t be right and you’ll be left having to deal with some sound frequencies being poor after a certain point.

What is better: 8 ohm or 4 ohm speakers? Are 2 ohm or 4 ohm speakers better?

What is better 4 ohm 2 ohm 8 ohm speakers

8, 4, and 2 ohm speakers aren’t necessarily “better” than one another. The correct answer is that it depends on the application and what stereo or amplifier is being used. The best impedance is the one that matches an amplifier or stereo’s impedance spec correctly.

Traditionally 8 ohms are used for home and some theater speakers. 4 ohm speakers are generally used for car use, with some 2 ohm models used at times (usually subwoofers).

For example:

  • 8 ohm speakers are used in home stereo systems and require 1/2 the current of a 4 ohm speaker. That means they can use smaller speaker wire as they can take advantage of home electrical systems that have a high voltage supply for driving speaker amplifiers.
  • 4 ohm speakers are used because car stereos and amplifiers (particularly car head units) can’t make large amounts of power in speakers as they have a very low 12V power supply. Reducing the speaker impedance from 8 to 4 means we can double the power for the same output voltage.

In fact, car stereos can only put out about a measly 15-18 watts RMS per channel, despite the exaggerated peak power ratings you may see in advertisements. That’s because they can only work with a 12V supply to develop power across a speaker.

Car amplifiers are able to deliver huge amounts of power to 4 and 2 ohm speakers by using an internal power supply that generates higher voltages for amplifying the speaker signal. Without that, it wouldn’t be possible to drive car speakers with tons of power to get boomy bass like many people enjoy.

When are 2 and 1 ohm speakers used?

Image of a Bose factory installed car amplifier

Factory-installed amps sometimes use 2 or 1 ohm speakers to develop more power without spending the money on amplifier designs using an improved power source.

2 and even 1 ohm (yes, 1 ohm!) car audio speakers are rarely used except for car subwoofers and some special cases for main speakers. Some factory-installed premium amplified car audio systems use lower impedance speakers to “cheat” using a “real” amplifier and save money.

That’s because they use the 2 or 1 ohm speaker to develop more power at each speaker without having to supply an amplifier with an internal power supply as is normally done. While it does technically work, it’s not a substitute for simply using a proper amplifier. 

They introduce other problems, like not being compatible with standard 4 ohm speakers when it’s time to upgrade or replace faulty ones. They also still can’t produce as much power as a decent aftermarket amp can with 4 ohm speakers, meaning you’ll still end up needing to replace them.

Speaker impedance matching

Example of matching speaker impedance to an amplifier

In order to get the most enjoyment (and power) for your dollar – along with avoiding damaging audio electronics – it’s important to match the speaker impedance (impedance load the amp sees at its output).

Here are some simple reasons to help you understand what happens when you don’t:

  • Using a speaker properly matched to the amplifier or radio’s minimum Ohms rating allows it to deliver the maximum output power it’s designed for.
  • Using a higher than specified speaker impedance will work. However, the speaker won’t be able to develop the full power that you paid for. As I mentioned earlier, a speaker needs more power to produce more volume, meaning you’ll lose volume because of this.
  • Using a lower than specified impedance speaker will cause an amp or stereo to run hot and can permanently damage the output transistors. Don’t do it!

While in some cases an amplifier might be able to shut itself off before it becomes damaged when a lower speaker impedance is used, don’t ever assume it will. Sometimes the damage still happens and you’ve just ruined an amp.

Most car stereos don’t have any type of overheating or high-current self-protection circuitry built-in so they’re likely to have their output stages destroyed.

Subwoofer impedance options

It’s a little bit different when we’re talking about car audio subwoofers, but the same rules hold true. Since a subwoofer channel on an amp usually has a lot power output on tap it’s not always an issue when using say a 4 ohm sub vs a 2 ohm sub with a 2 ohm min. amp.

However, as a general rule, it’s best to match the subwoofer impedance to get the power you’re paying for.

More great speaker articles

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What Are The Best Equalizer Settings For Car Audio? A Car EQ Guide

best settings for car audio featured image

Tuning your car sound system with an equalizer can be a frustrating mess and a waste of time if you’re not sure what to do. To make matters worse, there’s a lack of good information out there. I’d love to help clear things up!

In this article I’ll explain in clear words along with great diagrams and images:

  • What an equalizer is, how they work, and the different kinds
  • Why speakers and car audio systems benefit from using an equalizer
  • Some basic recommended EQ settings for many cases
  • How to set your EQ and tune your system the right way (using affordable tools that work great)
  • What to do if you’re still having sound problems
Contents

What are the best equalizer settings? The honest truth

Image of man thinking about car equalizer settings

The honest truth is that there’s not a true “best” equalizer or audio system setting. It depends on your goals, but ultimately, the best settings are those that let you tailor the sound in a way that pleases your ears the most.

However, I do have some general equalizer guidelines that can help you. I’ll make sure to cover those in a separate section below after explaining why an equalizer (EQ) is so helpful and the problems with speaker sound.

Sound systems for cars always have areas that need improvement if you really want to enjoy your music to its full potential. I’ll explain specifically what those are and the EQ settings you’ll need to fix that.

But before we get to that, let’s better understand what equalizers do and how they work.

What is an equalizer? How does an equalizer work?

Car audio equalizer examples

Examples of the most common type of car audio equalizers you’ll find are shown here. It’s possible to find good EQs in some aftermarket head units. However, you can also use an external add-on EQ to get great sound in your ride.

What does an equalizer do? Why are equalizers needed?

Diagram showing example equalizer settings to use

Equalizers allow you to improve the sound of a speaker system by boosting or cutting ranges of sound as needed where they’re lacking or have “peaks” (too much volume). The goal is “smoothing” the sound to remove harshness or a lack of bass, for example. Ultimately though, they’re also a great way to adjust the sound to your liking.

Equalizers allow you to correct problems with a sound system in car audio by boosting (increasing the volume of) or cutting (reducing the volume of) small sections (limited-width segments) of sound in the range of musical sound frequencies. These specifics “sections” are fixed around a central point called the center frequency.

In a perfect world, speakers would produce a perfectly flat sound output with no dips or harshness in the sound you hear. That’s impossible and there are always areas where the sound can use improvements.

The basic bass and treble controls included with many head units can’t correct much, sadly. Fortunately, an equalizer lets us correct many of these problems.

Equalizer bands and boost or cut (attenuation)

Equalizer band comparison diagram

Equalizers split up sound adjustment into small “bands” of sound frequencies centered around a single frequency. The amount of bands (amount of adjustment slots if you will) available determines how much control you have. The more bands, the finer and better the improvements you can make.

The amount of boost or attenuation you can apply is measured in decibels (dB) and usually there’s a maximum range of +/-9dB to +/-18dB. However, it depends on the particular model and design. 9dB and 12dB EQs are very common.

The number of bands an EQ has increases the amount of control you have over the audio sound adjustment range. More bands provide a means for better sound adjustment (you’ll be able to better correct speaker sound problems when tuning).

A 31-band EQ, for example, offers a lot of audio control but take can take a lot of time to tune a system. When choosing a more basic equalizer vs one with more bands, the best choice is the one with more bands

How does an equalizer work?

How does an equalizer work diagram

Equalizers work by dividing up the full range of sound into smaller sections called bands. These are centered around the EQ center frequencies. This section of sound is then increased or decreased as you like to adjust the sound. The bands are then recombined and output as a full range again with the EQ adjustments included.

Equalizers work by taking the full-range sound of each stereo channel (or mono, if it’s a subwoofer crossover, for example) and dividing them into “bands” using filters. Each filter directs the sound frequencies of that band, based around the band frequency, to a circuit that increases or decreases the volume of that range depending on your adjustments.

The sound from each of those circuits is then combined back together and sent out to your amplifier or speaker system. The end result is the same input sound but with EQ adjustments applied to it – not just a simple bass and treble improvement!

Some equalizers use a single set of controls for both of the front and rear speakers (one set of EQ controls for both stereo channels) while others have separate left and right channels for better tuning. Some provide EQ channels for both front and rear speakers.

In some cases, another smaller set of bands for subwoofer bass tuning is provided. This is often the case for digital equalizers like those in touchscreen car stereos.

Analog vs digital equalizers

Analog equalizers use electronic hardware such as op-amps, resistors, or integrated circuits to adjust the sound output as you adjust it. Digital equalizers (in most cases) are different in that they do this in software using mathematical software routines.

While both have their pros and cons, digital equalizers offer more features these days and save money since and space since they don’t need the added hardware to do the work. In many cases they also include adjustable crossovers that make system adjustment even better.

Basic recommended car equalizer settings – setting your EQ by ear

In dash car stereo with equalizer shown

In this section, I’ll share with you some basic steps and EQ settings when doing it by ear. In the section after this I’ll go the best way to do so: by tuning your system using the right tools.

Note that tuning audio in car systems by ear is more for correcting just the most obvious problems you can hear easily. To really know what’s going on with your system, you’ll need the right tools and approach I’ll share in the sound system car tuning guide below.

Getting started with the basics

You’ll want to do a few things before trying to adjust an equalizer because having too many adjustments means they can work against each other, meaning you might not get anywhere!

Image showing bass boost and EQ of car stereo turned off

My advice is to do the following before adjusting an EQ:

  • Disable any special audio modes like bass boost or “musical enhancement.” Turn the bass boost, if present, to “flat” or off.
  • Set the equalizer band adjustments all to flat. That is, to 0dB level, in the middle of the equalizer display (or to 0dB if it uses a number style control).

Diagram showing example equalizer settings to use

For many speaker systems (for example factory speakers with a factory-installed head unit), typically the sound is lacking in 2 or more areas:

  • Not enough bass
  • Too much mid range
  • Not enough treble (high frequency sounds like cymbals and string instruments)
  • Music has poor detail and doesn’t sound like the recording should

In this case, I recommend doing the following, being sure to use small increments of the equalizer and make changes slowly while listening carefully.

  1. Increase the bass a bit in the low-end range. This will be a band with a frequency of 60Hz or close to it – this depends on your particular EQ. You can then increase it a bit in the band above it and hear the results (ex.: 120Hz band, which is still bass but on the lower end of mid range sound & vocals).
  2. Increase the treble 6dB or so around the highest band on the upper end of the EQ, then continue increasing by 3dB if you hear an improvement. Continue until it sounds unpleasant to you, then decrease back until it’s better. This is usually a band with 16KHz or similar (some only go to 12KHz, which isn’t good, sadly). Treble can be a problem because of speaker placement being less than ideal in vehicles along with poor quality factory-installed speakers, too.
  3. If you hear “harshness” and the vocals and instruments in music sound like they’re grating on your nerves, you probably need to decrease mid range sound. Start with a band around 1KHz and decrease by about 3dB and listen for improvement. If there isn’t any, set it back to 0, then move up to 2KHz, 4KHz, and so on as needed.

Diagram showing typical EQ bands for adjustment

Note: I recommend using a music test track to do this. You can buy audio test tracks for download or CDs to buy online. Alternatively, you can use a song you know extremely well that you’ve heard on a high-fidelity system before.

The idea is to know how the music should sound with everything set up properly and judge your EQ settings by ear using test music.

Our ears are most sensitive in the midrange span of sounds so that’s often one of the biggest problem areas of speakers that need attention. Tweeters very often need some increase at the high end, too. It’s a huge problem with factory-installed tweeters that have a poor response (sound output) at the highest end of the sound range.

It’s also a common issue since many car tweeters are mounted in a location where they’re pointing away from you. That’s because tweeters are most effective with a directional installation where they’re facing your ears (called “on-axis”) and not to the side or away from them.

If not, you’ll hear get a fairly high loss in the treble range in music.

How to tune your system for the best EQ settings

Car audio real time analyzer examples

Some examples of your options for measuring and tuning your car audio speaker system. Of the 3, using a laptop and RTA software or smartphone app are the best values for the dollar. Today’s smartphone apps like AudioTool offer many of the same features as much more expensive options.

As I mentioned earlier, without question the best way to tune your system (find the optimal equalizer settings) is to use a measurement tool and find the areas that needed adjusting. To do so, you’ll need a real-time analyzer (RTA) and microphone. There’s simply NO WAY to get the best sound using only some music and adjusting it by ear.

In the past this use to be a serious pain in the neck – if you could even at all find an RTA to use. Until some years ago, real-time analyzers were far too rare and expensive. A dedicated portable unit like the AudioControl SA-3050, for example, often sold for $1,500. They were heavy, limited in functions, and battery power wasn’t even standard!

Thankfully, these days you can find get professional results using your laptop and RTA software (such as TrueRTA, for example) or use an RTA app with your Apple or Android phone.

Of the two, the most affordable and convenient option is to use your smartphone. For the sake of keeping things simple, I’ll cover using a smartphone and an RTA app. I recommend AudioTool for Android as it’s very good and while it’s not free, it’s cheap! ($7.99 at this time).

Using a smartphone app for tuning isn’t as accurate as say a much more advanced (and costly) real-time analyzer tool setup. However, you’ll still get pretty good measurements and results you’ll enjoy if you use it properly.

Using an RTA app for tuning (and why you need a good microphone)

Smartphone vs calibrated test microphone comparison diagram

Although you can use your smartphone’s built-in microphone to get you by, I don’t recommend it for tuning your equalizer/sound system. Built-in mics have poor frequency measurement performance compared to a real test microphone. Calibrated microphones also include a file to allow them to give a near-perfect measurement if your RTA supports it.

While you can use your smartphone’s built-in microphone with an RTA app to tune your system and set your EQ, I don’t recommend it. They’re poor for measuring sound and your readings will be off – way off in some cases!

Dayton Audio iMM-6 calibrated smartphone mic

You’re much better off buying an affordable calibrated microphone like the Dayton Audio iMM-6 at about $17. Each one includes a unique calibration file to help you get more accurate readings. You don’t have to use calibration (the mic is already pretty good) but it’s free, so why not get the most out of it?

How to tune a car equalizer

Using RTA for car audio tuning in car placement diagram

Your goal should be not to get perfect sound but to correct the areas where the speakers have bad peaks or valleys in the sound output.  For that, you’ll want more expensive tools and a lot more effort and time.

The most important thing is to have a pretty good idea of what’s going on with the sound output and correct the most troublesome sound points.

how to tune a car audio system using a real time analyzer diagram

To tune your system and measure where you need to make improvements using your EQ, you’ll want to do the following:

    1. Park your vehicle in a quiet area without outside noise that can interfere with your measurements. Leave the vehicle engine off.
    2. Set up your RTA to an “octave” mode similar to the number of bands on your EQ. Set the measuring speed to medium or slow. I personally prefer 1/3 octave (31 bands) mode but for those of you with fewer EQ bands, setting it to a smaller number of bands for the RTA display should help.
    3. Set your equalizer to all-flat (all settings at zero), bass boost OFF, and any other sound enhancement disabled.
    4. For systems using amplifiers, be sure you’re not using a bass boost for the subwoofers.
    5. With the RTA running and your microphone connected (set up the RTA’s mic option if needed), play a pink noise test track for measuring the system’s sound output with the RTA. (You can use an audio file or CD, but it needs to be high-quality and not compressed audio to make sure you’re generating real pink noise that’s not altered and that could result in bad measurements.) Note that some RTA apps can generate noise so you can connect the output to the AUX input of some head units.
    6. With the RTA running and held in a middle place between the seats near ear level, note areas where there are dips and peaks in your system’s response. 
    7. Begin adjusting the EQ a small amount for the bands in those spots and carefully watch the changes. Turning the EQ up or down too much for each frequency can cause you to have to constantly compensate by changing other bands as they interact. Do it a little at a time.
    8. A near-perfectly tuned system would appear as a nearly flat RTA line across the entire audio range. However, that’s not realistic. We’re aiming to get as close as we can to that then make custom adjustments later.
    9. Once you’re satisfied you’ve got it corrected (it takes a bit of time and patience!), save your EQ settings as a preset if it’s a digital equalizer. For analog (dial or slider type EQs) units, take notes for future reference.
    10. Final touches: play a music track (with good bass) that you’re VERY familiar with and know the sound on a proper system. Carefully make changes as you need to for what sounds best to you. In my experience, this is increasing the low-end bass (around 60Hz), lower midrange (around 120Hz), and higher frequencies (16 to 20KHz) depending on your hearing and taste.

The best goal isn’t to get perfect sound but instead (1) correct the worst problems in your sound system and (2) adjust the results to get the sound that YOU really enjoy with your music.

After tuning the system, feel free to use bass boost or other features if you think you like how they sound. However, be aware that a properly tuned system with good speaker performance normally doesn’t need a bass boost or gimmicks to make it sound right.

You should be able to hear sufficient bass when it’s adjusted optimally.

Those are instead for:

  • Making up for what your system is lacking (for example, poor subwoofer output
  • Occasionally adding that extra slam to your favorite music when you’re in the mood – just not every day
Important: Sometimes there’s only so much you can do. If you’re not able to tune your system enough and there are still terrible “dips” in the sound, it’s because of the speakers.

In that case, no amount of tuning can help. You’ll need to work on improving either the installation, the speakers, or both.

Upgrades that make a huge difference when your EQ can’t

Examples of recommended car audio upgrades for better sound

Equalizers are great but they can only do so much. Since they’re limited to a range of +/-12dB to +/-9db of sound adjustment typically, that means for problems exceeding that, you won’t be able to correct it enough.

Some of the biggest problems with car audio systems are very common based on what I’ve seen over the years. It depends a LOT on the particular vehicle, the speakers used, and much more.

In most case it’s due to one or more of the following problems:

  • Poor or no low-end bass: needs a subwoofer to be added or better subwoofer to replace the current one
  • Poor/very weak treble: Needs tweeters to be replaced and/or added. Also, consider moving tweeters to a better location facing the driver & passenger seats.
  • Music sounds “thin” and unnatural (poor midrange): Requires a speaker upgrade as this is a sign of poor speaker performance.
  • Distortion during playback especially at high volume: Insufficient power to drive the speakers. Consider driving them with an amplifier or replace a factory amplifier (if equipped) or a higher power aftermarket model.

The good news is that these days you don’t need to spend a ton of money on any of these. Each one can be found (with pretty good quality and sound, I might add!) for around $100 or less. In fact, by replacing all of the main components (a better sounding head unit, front and rear speakers, add a subwoofer for bass, driving speakers with an amp, and so forth) you’ll get great sound that no factory system can match.

More related articles you’ll enjoy

I’ve got some other great info to help you learn more:

Questions, comments, or etc?

If you’ve got questions or a comment feel free to post them below! Feel free to contact me here on my Contact page.

What Is A Class D Car Amplifier? How They Work And Why They’re Great

What is a class D car amplifier featured image

There’s a big range of car amplifiers out there and at first glance, they nearly all look the same. However, there are some big differences (and great benefits) you should know more about.

Thanks to modern technology, class D car amps can be one of the best choices for your money. But what is a class D car amplifier? How do they compare to others, and why does it matter?

Read on and I’ll show you!

Contents

Infographic – Class D car amp facts

What is a class D car amplifier infographic

What is a class D car amplifier?

Examples of class A/B and class D car amplifiers

You often can’t tell a class D amp apart from a regular class A/B car amp just by looking. That’s because they do the same thing, have the same features, and the main difference – how they work – is hidden inside. Some though are much smaller than other types of amps so they differ in size vs another amp with the same power rating.

Class D car amplifiers are audio power amplifiers that use a more efficient amplifier based on pulse width modulation (PWM) technology.

Unlike some misleading or misunderstood descriptions, class D amplifiers are not “digital amps.” Instead, they still work with analog (non-digital) signals although they use a different approach.

In the past due to the limitations of technology and sound quality at the time they were used only for powering subwoofers since the lower sound quality they offered wasn’t noticeable in the low frequency range of bass in music.

The good news is that car audio technology & electronics have improved a lot. You can now find a wide variety of class D amps to drive full-range speakers, subwoofers, or both – all from one small amp!

The benefits of class D amplifiers

These types of amps have become more and more popular because of the benefits they offer:

  1. High efficiency: Class D amps typically have about 85% efficiency as they work, meaning they use a lot less electrical current than class A/B and other amps. This also means you can often use a smaller gauge for power wiring which saves money.
  2. Compact size: Since they waste less power, they don’t run hot like other amps and can be made smaller in size than traditional car amplifiers. This also saves money by reducing the metal needed for the amp’s chassis.
  3. More power for your money: They’re capable of delivering more power since the power limitations of other amps make this harder. Class D amps can provide a lot more power for the same money as very expensive amps of the past. Since heat is not a problem, they can deliver power (watts RMS, not “peak power”) without the side effects.
  4. More installation options: Obviously, a smaller amp can fit in more places. However, since they don’t generate much heat, that means you don’t have a risk of them overheating like other kinds. You can fit a class D amp in places with no or very little airflow or space: under seats, inside motorcycle storage containers, and even inside a dashboard near the head unit.

Since the draw less electrical current (amps) than older models, some can be installed using the factory radio wiring. This means you’ll avoid the need to buy & install extra wiring as you’d normally have to. Nice!

What does car amplifier class mean?

Teacher discussing car amplifier classes

An amplifiers class is a name used to categorize an amplifier by the technology used for the operation of an amp. All audio amplifiers fall into one of a few classes. 

Amplifier classes have been around for decades with the number of classes increasing as technology has improved.

In addition to D, here’s a list of others:

  • Class A: The most inefficient but highest-fidelity amplifier type. Not that popular and usually reserved for audiophile use.
  • Class B: Not very common – an older amp class where amplification splits up the positive and negative halves of the audio signal. More efficient than class A, amps but lower sound quality as a result of the way it works. These were used in some vacuum tube amps years are go but are outdated now.
  • Class A/B: For many years, the most popular because they’re a good all-around compromise between low cost, sound quality, and efficiency. These types of amps combine the way class A & class B designs work. However, their power efficiency is somewhere around 50-65% so they still waste a fair amount of power. 

How does a class D car amp work?

How does a class D car amplifier work diagram

Diagram showing how a class D amplifier works. Unlike other designs, this one uses a very high-frequency switching frequency circuit to mix the incoming signal with a waveform to create an on/off series of pulse width modulation (PWM) signals. This is then used to drive power transistors where it’s amplified. The amplified result is then “smoothed” to recreate the original musical signal and filtered to remove high-frequency noise added as it works.

As I mentioned earlier, class D amplifiers are not digital amplifiers as they’re sometimes called for some reason. They don’t convert a stereo’s musical signal into a digital series of numbers; rather, they use an analog square wave design based on pulse width modulation (PWM) technology.

Here’s how a class D car amp works:

  1. The low-level input signal from the head unit is modulated, or altered, by a high-frequency circuit that changes the audio signal into a series of square on/off signals that vary in width based on the input level.
  2. These signals are then used to drive power transistors which amplify them. The square wave signals are amplified to a higher voltage from the amp’s switching power supply and are now capable of delivering high power to speakers. Because the square waves turn on and off rapidly, the transistors never stay switched on for long reducing the power used and wasted.
  3. The amplified square waves are smoothed by electronic circuits that change them back into an amplified version of the original curved musical signal.
  4. Before the speaker output terminals, filters remove high-frequency noise from the output signal as the amp works to eliminate it from the range of sound you can hear. The output is an amplified version of the input signal with a high power capacity.

Nearly all class D amplifiers (unlike class A or A/B models) use a special integrated circuit (IC) that handles chopping up the audio signal and driving power transistors. Some miniature versions are designed to be an “all in one” product and drive the speakers directly. These are usually used for lower-power computer speakers or miniature home stereo amps.

Budget car amps often use an off-the-shelf class D amp controller chip while brand names more often use a more advanced custom IC.

Just like other amps, many also offer high level inputs to work with factory stereo units.

Note: You may see some home & car amplifiers advertised as being “class T”, “class G”, or some similar name. Despite how they sound, those also are just renamed versions of the same basic class D design with some custom changes or tweaks.

Are Class D amplifiers high fidelity?

Man listening to amplifier fidelity

In the strictest sense, no, these types of amps are not high fidelity unlike class A amps with super-low distortion specs or the sound quality of high-end class A/B designs. That’s because the sound fidelity of class D amps must be compromised a bit in order for us to benefit from the efficiency they offer.

In order to provide world-class sound clarity, Class A amps waste a lot of power which is turned into heat. However, they’re still preferred by some people because they offer no-compromise audio amplification, ultra-low distortion, and reproduce the musical signal very faithfully.

High-end class AB amps, while not quite as good as class A, also offer excellent sound quality at the added expense of a higher price tag. Even budget and mid-level class A/B amps can offer high-fidelity sound if they’re properly designed because of how the technology works.

Because class A/B amps offer good sound quality in addition to decent efficiency and are cheap to build, they’ve been the most common type of car amplifier for years. Despite that, class D amps have improved and are becoming more popular.

Here’s why class D amps are lower fidelity:

  • Class D amps use PWM technology to convert the original signal into square waves and back again. This means a small amount of fidelity can be lost. Any time a musical signal is converted some accuracy is lost.
  • As they work, more noise is unintentionally added to the sound signal than other kinds of amps. Because of this, these amps often have a lower signal-to-noise (SNR) ratio than their counterparts. Generally speaking the higher the SNR, the better.

Don’t let that give you the wrong impression, though – today’s amps are very good!

They’ve improved a lot – but quality matters!

5 to 10 years ago, the class D amps I tried were disappointing. The good news is that today’s amps are much better. As long as you shop carefully and pay attention to the details, you’ll be happy with the sound.

For example, the Alpine MRV-F300 4 channel class D amplifier I reviewed here is a great-sounding little amp that I enjoyed.

Most people will find it nearly impossible to tell the difference in sound quality when comparing a very good class D amp to an average A/B amp. Unless you’re extremely picky about sound quality, it shouldn’t be a problem.

If you’re only planning to use an amp for bass the sound quality doesn’t really matter since we can’t hear the difference for bass frequencies. That’s why they were used only for subwoofer amp before the technology improved.

What is a class D mono car amplifier?

What is a class D mono car amplifier

Class D mono car amplifiers are designed to deliver a lot of power to subwoofers for high-volume bass that really slams. Unlike full-range amplifiers, they’re limited to only producing bass.

Most mono car amplifiers have some common features:

  • Lower speaker impedance (Ohms) rating: Many can handle down to 2 ohms or even 1 ohms for maximum power delivery.
  • Not full-range capable. Most can’t be used for coaxial or component speakers, for example. The audio they can produce is limited to only a low-end bass range.
  • High power output: These days, class D mono car amps have power ratings such as 500W RMS, 750W RMS, and even 1,000 watts or more! This is made possible by the class D PWM efficiency.
  • Subwoofer level control: some models provide a rotary knob to adjust the amp’s volume from your dashboard.
  • Adjustable bass filter: Typically, even though they can’t produce sound above 250Hz or so, you can adjust the crossover output cutoff from 20 to 250Hz, depending on the particular amp.

While they use a single monoaural (mono) channel output, some have an extra set of speaker terminals to make it easier to connect multiple subs if you like.

Are Class D amps good for subs?

Most importantly the thing to understand is that these mono amps (also called “monoblock” amps) are designed only to deliver a lot of high power to subwoofer and nothing more. In this regards they’re excellent for subs!

They offer a higher watts-per-dollar value than any other kind of amplifier. In fact, you can find some today that can deliver 500 watts RMS (or higher!) for $100 and below.

Is a class D amplifier better?

Are class D amps better man wondering

There’s not a true “best” amplifier class – at least not currently. Each one has strengths and weaknesses, meaning it comes down to what’s best for you. For example, if you’re like most people and want good sound but the best value for your money, then yes, it’s likely better in that case.

However, when it comes down to what matters for most people, class D car amps are better in most but not all categories that count.

Here’s a comparison of the different amplifier classes and their pros and cons:

Car amp class comparison diagram

Car amplifier classes comparison diagram

A diagram comparing the main things you care about with audio amps. As I mentioned earlier, class A/B amps are a good compromise between sound quality, cost, and power. However, as you can see here, class D amps these days now are a better value and offer more for the money. They’re a better all-around choice for most people who don’t need audiophile-level sound quality.

Like I mentioned before, class D amps now are becoming more and more popular along with being a better value for most people. Unless you’re after the best possible sound quality you can buy, you’ll get more power for your dollar, an affordable price, and easier installation for your money.

As you can see in my diagram above, class A amps excel in sound quality (they’re ultra-low in distortion and do a great job of reproducing the musical signal) but fall short in nearly all other areas. 

A/B class amps were for many years the best all-around choice. They offer very good sound quality even with budget models, fair power availability, they’re affordable, but they’re not as compact. Class A amplifiers aren’t commonly available for car audio much anymore so they’re not really a competitor.

Class D amplifiers as you can see have more pros than they do cons – they’re smaller, you can get more power for the money, and they use less electrical current, but aren’t audiophile-level in their sound quality. When shopping you can find 4 x 100 watts RMS power model vs a 4 x 50 watts RMS power A/B amp, for example.

Ultimately, for most people class D amps are great and the best choice if you’re not very picky about sound quality. Don’t get me wrong – today’s models have very good sound quality – just not high-end, audiophile-level sound. If that’s not what you’re after you’ll find them very enjoyable.

Class D vs class A/B car amplifiers

Class A/B vs class D amplifier operation diagram

A diagram comparing the operation of class A/B vs class D amps. Unlike class D amps, A/B models don’t change the original signal but instead, amplify it and split it into a positive and negative half to drive output stages. Class D amps take advantage of PWM principles and only drive the transistors part of the time, saving power use and wasting less.

What is a class AB car amplifier?

Class A/B amps have been around for decades and range in price from both super-budget levels to high-end designs. In all cases the basic design used is the same: the input signal is used to drive output transistors with a positive and a negative half, boosting the input using the amp’s internal power supply voltage to drive speakers.

Due to how they work, some power is wasted (around 45-35% or so, depending) and ends up as heat that warms the heatsink (heavy metal chassis). They offer very good sound quality as they don’t change the audio signals but instead only amplify them.

Class D circuitry uses PWM principles to save power wasted as they only switch the power output transistors part of the time. Unlike class A/B amps, they do change the input signal: it’s converted to square waves that are converted back to smooth waves just like the input signal as they leave the amplifier.

Are Class D amps better than AB?

Pioneer GM-D9605 review test amp rack image

Class D amps can offer more power and/or more amp channels in the same or smaller size than class A/B. This Pioneer 5 channel amp, for example, can deliver more power to 4 speakers and a dedicated subwoofer channel than A/B amps of the same size. For that reason, you could say it’s better.

There’s a slight difference in sound quality that varies by brand and the quality of the design. As a compromise, the signal to noise ratio is somewhat worse than A/B designs. For example, 90dB or so is more typical for good ones while A/B amps often start at 90dB and 100dB isn’t uncommon.

It’s not really the case that class D amps are better than A/B but to most people they are. For example, not that many people care about the finer sound quality specifications like noise or SNR.

They care more about the power they’ll get for their money – in this regard, D class amps are better. They’re also easier to install in many cases since they’re smaller.

I think the best response is to say they’re better for power, size, and value than most A/B amps. They’re not better for higher-end sound quality. There are, however, some class D amps with excellent sound quality. 

You’ll have to spend more for those as they’re more advanced designs in order to produce a higher level of sound quality than most.

RB-XD400/4 amp side view

Some class D amps like this one from JL Audio offer excellent sound quality that can compete with most A/B amps. They’re more expensive, though.

Can I use a marine class D amplifier in a car?

Example image of a Rockville marine amp installed in a car

A marine amp installed for in-vehicle use & testing. Don’t hesitate to use a class D amp yourself if you like!

Yes, you can install a marine amp in your car, truck, or motorcycle!

As a matter of fact, they offer some great installation options you might not have otherwise!

Here’s a list of some great options possible and problems they solve:

  • Class D marine mini-amps are excellent for reliable power and great sound in motorcycles since they can fit in smaller spaces and won’t overheat.
  • A marine amp is suitable for outdoor vehicles and is far more affordable than specialty amps from the vehicle manufacturer.
  • You can build a sound system without a stereo! Some class D marine amps have a built-in Bluetooth receiver & controller option that makes this possible.

Image of marine amp with Bluetooth in classic car

Marine amps offer some excellent solutions for some special case installations like in classic cars. Rather than spend a ton of money for custom fabrication or metalwork you can use an amp for a direct, easy-to-install sound that works great.

They’re really aren’t any “cons” to worry about, aside from the cosmetic color and style. Additionally, when shopping that means it’s possible to have even more options and you can possibly find a great deal.

More articles about amplifiers and speakers

I’ve got some other great info to help you learn more:

Questions, comments, or etc?

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