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

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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

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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 impedance DC resistance
2 ohms 1.2-2 ohms
4 ohm 3.1-4.0 ohms
8 ohm 5.7-8 ohms
6 ohms 4.0-6 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

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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 ohms 4 ohm
6.0-8 ohms 8 ohm
1.2-2 ohms 2 ohms
4.0-6 ohms 6 ohms
0.5-1.0 ohms 1 ohm**
12-16 ohms 16 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

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

Something on your mind? Feel free to leave a comment or question below.

How To Tell The Impedance Of A Speaker And Understanding Speaker Ohms

How to tell the impedance of a speaker featured image

We take for granted how certain stereos and amplifiers need  2, 4, or 8 ohm speakers to work right. But what is speaker impedance?

And how can you tell the impedance of a speaker if it’s not on the speaker or you can’t find it?

Great news – it’s not that hard! In this helpful article, I’ll explain how speaker impedance works, how you can measure speaker impedance (Ohms), and much more.

There’s also a handy speaker Ohms chart to help you identify what impedance your speaker is to know for sure.

Contents

How to tell the impedance of a speaker

Let’s cover the main ideas before going into more detail as I cover each topic more.

How to find a speaker's impedance
  • If the Ohm rating (impedance) is not available on the speaker, you must 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 category. (see below for more detail)
  • A speaker’s impedance is usually listed on the speaker magnet, packaging, and/or box and specifications. This is not always the case, however, as it depends on the manufacturer and model.
  • The total impedance changes with frequency as speakers don’t act like resistors but instead have inductance which opposes the flow of current as the audio signal frequency increases. You can calculate impedance based on the formulas included here. Note: you won’t need this just to determine the general impedance range of your speakers.

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 way you can be 100% certain and avoid problems with your stereo, amplifier, and crossovers.

You definitely don’t want to use a speaker with lower impedance than expected as it’s possible to damage your stereo or amplifier permanently!

What is speaker impedance? (Speaker Ohm ratings explained)

What is speaker impedance diagram

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.

Unlike standard electrical conductors, 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. This is called inductive reactance.

How does speaker impedance work?

Magnetic fields are created as current flows through the tightly wound wire coil. These fields have an opposition (resistance, also called reactance) to the current flowing through the coil wire. (Similarly, many other electrical components like motors have this too).

Because of how inductance works and the physics involved, the speaker “impedance” (total resistance) isn’t a simple addition of the resistance and the inductive reactance together.

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

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.

How to calculate speaker impedance

How to calculate speaker impedance diagram

If you’re a math person, you can see here how speaker impedance is calculated. As I mentioned, it’s the geometric sum of the resistance in the voice copper wire winding and the inductive reactance at a given frequency.

The most important thing to understand about speaker impedance is:

  • The speaker impedance is always equal to or greater than the voice coil wire resistance. You can measure this with an Ohm meter.
  • The impedance number on a speaker is a general guideline for compatibility, not exactly what the speaker measures.
  • The impedance changes slightly (goes up) as the frequency being played increases.

In fact, if you were to use a test meter to measure the Ohms (impedance) of the voice coil on a speaker, you’d find a reading of about 3.2-3.6 ohms or so for a 4 ohm speaker and 6 ohms or higher for an 8 ohm speaker.

Example of calculating speaker impedance

Let’s take an example. We’ll use an example speaker and real-world specifications then do the math.

Calculating speaker impedance example parameters used

Example parameters to use from a real speaker for the voice coil’s resistance (Re) and the winding’s inductance (Le).

Example of calculating the speaker impedance using 1kHz as the frequency:

  1. Calculate the inductive reactance. Use the formula given earlier Xl = 2*Pi*Le*frequency: 2*3.14159*.000028*1,000 = 0.1759 Ohms (Ω)
  2. Find the total impedance (represented by “Z”). Find the root of the sum of the squares of both Re and Xl: Z = ( (3.0)^2 + (0.1759)^2)^-1 = 3.005 Ohms (Ω)

Therefore, for our example speaker, the total impedance at 1kHz is 3.005 Ω, only a tiny bit higher than the voice coil’s own resistance.

This is because (1) most speakers have a very small amount of inductance, and (2) speakers work in the audio range and no higher than 20kHz, meaning the inductive reactance will be limited.

Speaker impedance due to the resonant frequency

That’s not to say that speakers never have a high impedance. In fact, at their resonant frequency where they behave differently, the impedance can be HUGE! In fact, as high as 50 ohms. However, that’s a separate topic.

(Note: as you see from the example speaker’s specs, the parameter “Fs” tells us the resonant frequency of 84.8Hz is where that happens for this particular speaker)

How to measure speaker impedance

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 the lowest range that measures units of 1, 0-10, 0-20, or auto-ranging and the meter will measure it accordingly. Hold the test probe leads firmly against clean metal on the speaker terminals with speaker wire removed.

To measure the impedance of a speaker you’ll need a multimeter (test meter with multiple functions) or a dedicated Ohm (resistance) meter.

Use the following steps:

  1. Switch on the meter and set it to measure Ohms on the lowest range. This is often the x1 range, 0-10, 0-20, or auto-ranging 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 firmly 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 measured value to determine the closest approximate speaker impedance (see my chart below for help).
  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.

The important thing to bear in mind is that you won’t measure exactly 4 ohms, 8 ohms, etc. Speakers are given an impedance rating for stereo purposes that are approximate – or close to – what you’ll measure with a test meter.

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

See my notes below for how to measure those correctly.

Selecting the correct resistance (Ohm) range for 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) then go up if necessary.

That should almost never happen – but in the case of a poor connection, blown (or almost blown) speaker, strange things can happen and you might get a reading that’s far outside the speaker’s normal impedance.

In my experience, however, that’s very rare.

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

How to measure speaker impedance when there is a crossover

Diagram showing where to measure speaker impedance of tweeters with crossover

Tweeters are one of the most common types of speakers with a crossover. To measure speaker impedance on them, you’ll need to place the test meter’s probes around the capacitor crossover. Otherwise, the reading will be an open circuit or far too high.

Measuring speaker impedance where crossovers are used is a bit of a problem. That’s because capacitors, which are commonly on tweeters as a high-pass filter, act as an open circuit when measuring resistance.

Obviously, that’s a problem as you’ll never get a correct reading if you use the test leads on the speaker wiring.

To avoid this, you’ll want to measure around the capacitor, if used, which is normally on the positive speaker terminal. You should be able to then get a correct reading.

For 2-way speakers, in many cases, no crossover is used on the woofer. In some cases, 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.

Diagram showing where to measure speaker impedance with crossover use

For 2-way crossovers, the same applies, too. Following the diagram above, your main concern is avoiding measuring across capacitors.

Speaker impedance example chart (use with speaker measurements)

Speaker impedance label and ohm meter examples

An 8 ohm speaker, in the real world, will have a resistance measurement less than its 8 ohm rating. That’s normal and is due to how the speaker is made. Speakers do not have exact impedance values but instead will fall into a general range close to their rating. You can use that range to identify their impedance if you don’t know it.

To use this chart, take the speaker resistance measurement you got from the instructions earlier and use it to compare to the measurements here. You’ll see your speaker should fall into of the commonly sold speaker impedance standards.

Speaker impedance measurement chart

Speaker measurement range* Speaker impedance rating
3.1-4.0 ohms 4 ohm
6.0-8 ohms 8 ohm
1.2-2 ohms 2 ohms
4.0-6 ohms 6 ohms
0.5-1.0 ohms 1 ohm**
12-16 ohms 16 ohms**

*(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 other speaker systems, but aren’t very common)

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

4 ohm vs 8 ohm speaker power comparison graph

This graph shows what happens when a higher impedance speaker is used with an amplifier or stereo rated for a lower impedance speaker. As this example shows, using an 8 ohm speaker in the place of 4 ohm ones means it will develop 1/2 the power and consequently, lower volume than a 4 ohm speaker.

Using a speaker that’s not matched to the stereo or amplifier it’s rated for can have relatively minor – or even horrible – results depending on which case we’re talking about:

  • 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.

For example, if you were to use 8 ohm speakers in the place of 4 ohm car stereo speakers you won’t damage anything, as less current will flow to the speaker. 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.

Ohm’s Law and speaker power

Car amplifier power output formulas image

A radio or amplifier is designed to output a certain voltage level for a given volume and so higher impedance speakers won’t have the same power available at the same volume level. That’s because the power to a speaker depends on the voltage available.

By the electrical formulas called Ohm’s Law, P (power, in Watts) = Voltage^2/R (speaker Ohms)

For a low volume (2V output from an amplifier) a 4 ohm speaker would have 1W of power available. An 8 ohm speaker, however, would have only 1/2W. That means for the same amplifier or radio volume, higher impedance speakers can’t produce the same volume.

How does speaker impedance affect sound?

Using the wrong speaker impedance can affect the sound in a few ways:

  • If you mix and match 4 ohm tweeters with 8 ohm woofers, for example, they’ll be mismatched and at some point won’t sound right as the power increases because their volume levels won’t be the same.
  • Using the wrong speaker impedance with speaker crossovers can have a very big impact on the crossover frequency (it will be shift a lot) and will dramatically affect the sound output. Your speakers won’t sound right, can have a lot more distortion, and will generally be much less pleasant to listen to.

What happens to a car stereo if a speaker has a lower impedance than the stereo is rated for?

Using a lower impedance speaker than your stereo or amplifier is rated for is a terrible idea and should never be done! That’s because it’s not designed to handle the excessive amount of current it will have to supply thanks to the decreased resistance of the lower speaker impedance.

If you’re lucky the unit will go into “protect mode” in which it shuts off until the condition is removed and it’s safe to operate. However, from my experience, many electronics become extremely hot and can burn out their output transistors meaning they’re permanently damaged.

Don’t risk it! Always check the minimum Ohm rating of your equipment and be sure to follow it. Never assume the amp, radio, or receiver, etc, will be able to protect itself from damage.

Speaker impedance and crossovers – yes, it’s important!

2 way speaker system and crossover diagram

Crossovers are designed for a specific speaker impedance. Changing the speaker impedance means you’re changing how they function and shifts the crossover frequency, giving worse sound and potentially adding distortion that wasn’t there before.

When using speaker crossovers, it’s really important to understand that you can’t change the speaker load (speaker impedance they see connected) as the results won’t be good.

Changing a 4 ohm speaker to an 8 ohm one, or vice versa, will have a huge impact on the sound because the crossover cutoff frequency will change greatly since it depends critically on the speaker load used.

As a general rule:

  • Doubling the speaker impedance will halve (decrease) the crossover frequency.
  • Halving the speaker impedance will double (raise) the frequency cutoff.

For tweeters, increasing the tweeter impedance means you’ll be allowing in more bass & midrange, leading to poor sound since tweeters can’t produce those ranges. For woofers, that means introducing poor-sounding midrange or treble that they’re not suitable for.

In both cases, just remember that the crossover frequency changes inversely proportional to the speaker load you’ve increased or decreased.

Note: When reducing tweeter volume, using an L-pad or properly designed L-pad resistor network will properly maintain the speaker load the crossover sees so it won’t affect the sound.

More great speaker-related articles you’ll love

Check out my other articles as I’m sure you’ll find something useful!

Questions, comments, or suggestions?

Got questions, comments, or feedback? Feel free to leave a comment below or you can reach me directly via my Contact page here.

The Speaker Wiring Diagram And Connection Guide – The Basics You Need To Know

Image of home and car speakers to be connected

We all enjoy music and speakers make that possible – but it’s confusing if you’re not sure how to connect them the right way.

In this post, you’ll find clear and detailed speaker wiring diagrams that to help (and that you can print out if you like, too!).

I’ll go into detail about the right and wrong way to wire speakers and connect them properly to your stereo or amplifier. It’s actually pretty simple once you learn the basics.

Contents

Printable speaker wiring diagram

Click on the image to enlarge it or click here for the Adobe .pdf version you can download and print.

Image of illustrated speaker wiring diagram

Speaker basics and speaker wiring explained

1.  What is speaker impedance? (the “Ohms” rating)

Speakers, much like other electromechanical devices, all have an electrical resistance to the flow of electrical current, much like a standard resistor, a light bulb, or many common items you’re familiar with.

The difference is how they behave when music is present when they’re connected to a musical amplifier of some sort.

The resistance value comes from a long coil of wire inside each speaker called a voice coil. A voice coil is a coil of wire that, when placed inside a magnetic field, makes the speaker move and produce sound when driven by an amplifier.

Example of a speaker voice coil close up

Speakers contain a long wound loop of wire called a voice coil. Loops of wire have a property called inductance which affects a speaker’s resistance value depending on the frequency (sound range) being played.

As they have electrical properties that include inductance and capacitance, their “total resistance” can actually change with the music slightly. Because of this, there’s some extra math needed to figure out the total resistance.

The word used to describe this is called impedance.

Speaker impedance is just a more advanced way of finding the total resistance, and by tradition is measured in units called “Ohms.”

The good news is that you don’t have to worry too much about the details – it doesn’t matter for basic speaker use, and long as you understand the basic rules you’ll be fine!

2. Stereo and amplifier minimum impedance ratings

All amplifiers of any type – where it’s a car stereo amplifier, home stereo receiver, home theater amplifier, and so on, have a minimum Ohms (impedance) rating. It’s important that you pay attention and don’t exceed the minimum speaker impedance rating.

This is because as the impedance is lowered, the electrical current increases and the stereo has to do more work. This increases the amount of stress and heat it has to handle.

If your stereo is labeled by the manufacturer as being “8 ohm speaker compatible” or similar, that means connecting lower impedance speakers can cause excessive heat and possible damage very quickly.

For example, connecting a 4 ohm speaker to an amplifier that is labeled as working with 8 ohm speakers would mean it would have to produce double the electrical current to the speaker!

Image of the rear of a stereo receiver and speaker impedance terminals

Image of the rear of a home stereo receiver/amplifier. The recommended speaker impedance ratings are usually listed above the speaker wire posts. A home stereo, for example, may often list 6-16 ohms as being ok for use.

Also, attempting to wire two 8 ohm speakers in parallel to an 8 ohm stereo would have the same effect. (Two 8 ohm speakers in parallel is equal to 4 ohms total that the amp will see)

I’ve seen many attempts by people who had friends who claimed they could “boost the power” or “get more power” by some claimed trick, but it doesn’t work. They ended up with a burned-out amplifier.

An amplifier can only handle so much heat and stress before it fails, so be sure to observe these rules. Be sure you wire speakers to meet the minimum Ohm rating you need.

Remember: don’t use a speaker impedance below the rating given by the manufacturer. Overheating or permanent damage can result. I’ve seen it happen!

3. What is speaker polarity?

Speakers are different than other devices in that they work using alternating current (AC) instead of direct current (DC). This is good news! It means you can’t harm your speakers in most cases by having the positive (“+”) and negative (“-“) wiring reversed.

Unfortunately, it gets just a little bit more complicated when we use more than 1 speaker.

Speak polarity and why you should match speaker connections

As I mentioned, speakers work by moving a cone back and forth in order to produce sound. If you wire 2 speakers in a stereo with different polarities (for example, one has positive and negative wired as labeled, and the 2nd speaker has the opposite) an interesting thing occurs: they’re out of phase and some sound cancels out.

The result is a strange and poor sounding stereo. In most cases, you’ll notice a lack of bass sound and it won’t sound pleasing to the ear as expected.

Diagram showing speakers in and out of phase

When speakers are wired the opposite of each other sound waves cancel out. When wired the same, sound waves add together for more sound.

Speakers that are wired differently sound poor because much of the sound is canceled out. Basically, it’s simply because sound waves from one speaker are moving in the opposite direction of the other speaker – and if they’re close to the same time and frequency range, often they cancel out.

This is why when 2 woofers are placed in a box and are wired in parallel but with opposite connections to each other, they are “out of phase” and have almost no bass! It’s because they are doing the opposite work rather than working together to produce more sound.

While one is moving up, the other is moving the opposite direction, and so on.

So the most important thing here to remember is to wire speakers consistently the same way as each other.

4. Wiring 2-way and 3-way speakers

2-way speakers, such as home stereo or car audio component speakers, are those which come as a pre-designed speaker set and use a crossover. The job of a crossover (also called a passive crossover, because it use basic capacitors and inductors rather than electronics) is to restrict the music production each speaker tries to produce.

For example, tweeters can’t reproduce bass frequencies (and can in fact be damaged by them) so a 2-way speaker crossover is used to prevent this. Similarly, a woofer can’t produce high pitch sounds well and is prevented from doing so.

Unlike standard separate speakers, 2-way and 3-way speakers that have a crossover can only be used in parallel and not in series.

This is because unlike separate speakers with no crossovers, in this case, many sounds will be filtered out. What this means is that little to no sound would be produced if another 2-way speaker is connected in series.

Image for 2-way speaker diagram examples

Therefore if you have a home stereo or car stereo in which 2-way speakers are used, you’ll have to add more 2-way speakers (if the total impedance can be supported by the amplifier) or add more amplifier channels for more sound.

5. Doubling the number of speakers or amount of power does not double the volume

In some cases, more speakers can be added to increase the amount of volume you can get or to place speakers in more rooms, more locations in your vehicle, and so on. You also may have wondered what would happen if you bought an amplifier with twice the power of your present one.

There’s one important thing to understand, however: having 2 or 3 speakers instead of one does not double or triple the sound. It increases a few decibels (dB) for each speaker added.

Doubling the power does not double the volume either.

This is because of how the human ear works and the physics of sound, along with how speakers work and how much volume they can produce for a given amount of power.

Generally speaking, the human ear will hear a very small amount of volume increase for each doubling of acoustic power: about 3 decibels (dB). For most people, the small amount of volume increase you notice when turning up a volume knob 1 notch is somewhere around 3dB.

Example volume produced by a typical speaker at different power levels:

  • 1W = 89 dB
  • 2W = 92 dB
  • 4W = 95 dB
  • 8W = 98 dB
  • 16W = 101 dB
  • 32W = 104 dB
  • 64W = 107 dB
  • 128W = 110 dB

So as you can see, doubling the amount of power you can drive a speaker at does not mean you’ll double the volume. It increases it a very small amount (as far as your ears are concerned).

You can also see from above that really cranking the volume takes a lot of power!

How to get more volume from speakers

The best ways to get more volume  in most cases are:

  • Use more efficient speakers (speakers that produce a higher dB volume at 1W of power – higher is better)
  • Add more speakers if you have an amplifier that can support it
  • Use higher-power rated speakers and a larger power amplifier if a lot more volume is your goal

Most people need an amplifier that can produce enough volume to fill a room or vehicle and turn up the volume from time to time. I like to use 50W or higher per channel as a good rule of thumb when buying an amplifier.

How to read speaker positive and negative labels (+ and -)

Home stereo and car speakers normally often use a red or plus sign “+” to indicate the polarity for the speaker wiring terminals which you connect your wiring to.

Here are a few things to know there as well:

  • In some cases, a black dot or a red or black stripe is used to mark the positive terminal
  • If a speaker has terminals of 2 different sizes, the larger of the 2 is normally the positive one
  • For speakers with wire already attached, typically the brass or golden-colored wire is the positive one
  • For speakers with wire attached but the same colored wires, most have some small printing on the positive wire – be sure to check closely

Summary

Here I’ve provided you with a speaker diagram showing basic connections, I explained several important things you need to know about speakers and speaker wiring. Hopefully I’ve given you more understanding about how to connect speakers and get the most enjoyment out of your system.

Have questions, comments, or suggestions? Be sure to leave a comment below or send me a message.

Confused about tweeters? Here’s a helpful guide explaining what tweeters are and what they’re used for.

Interested in bridging your car amp?  Find out how to bridge a car amp in this post.