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

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.

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:
    Xl = 2*Pi*Le*frequency: 2*3.14159*.000280*1,000 = 1.759 Ohms (Ω)
  2. Find the total impedance (represented by “Z”): Find the square root of the sum of the squares of Re and Xl:   
    Z = √[ ( (3.0)^2 + (1.759)^2 ] = 3.142 Ohms (Ω)

Therefore, for our example speaker, the total impedance at 1kHz is 3.142 Ω, only a little 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!

diagram showing how a 2-way speaker crossover works

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.
About the author

Marty is an experienced electrical, electronics, and embedded firmware design engineer passionate about audio and DIY. He worked professionally as an MECP-certified mobile installer for years before moving into the engineering field. Read more »

Your comments are welcome.
  1. I have a Rockville G- 20 20 watt guitar amp with Bluetooth
    the speaker is a 6.5″
    There is nothing written on the speaker
    My ohms meter reads 7.7
    what is the Ohms for this speaker 4 or 8Ohms? Help< lol

  2. Hi Marty,

    I have four downstairs rooms with an amplifier and two speakers in the lounge, and a set of 12 switches supplying sound via speaker cables buried in the walls to these two speakers and to three other rooms, each also having two smaller speakers.

    About a year ago a fuse blew in the amplifier. I got some replacements of the same size and ohm rating, and renewed it, but the replacement immediately blew. I phoned up a local repair shop and explained the situation, and I was advised that it probably wasn’t worth taking the amplifier in to them for inspection and possible repair, so since then we’ve been using a couple of stand alone speakers via our wifi system.

    We spent this Christmas at our son’s house, and he gave me a spare amplifier which is suitable for two pairs of speakers, but before trying to fit it, and perhaps damaging it, I decided to check the impedances of the speakers we have fitted.

    I should say that none of our wired speakers show what impedance they should have, but I tested them all, including the cable runs, from the above mentioned set of switches, not so much to get an accurate idea of their individual impedances, but more to see whether any of them had a dangerously low impedance that could be causing the fuse to blow.

    I found that most of the readings varied between 8 and 20 ohms, except for two speakers, one which varied between 140 and 190 ohms, and the other which showed no change on testing, i.e., the meter reading stayed at 1 ohm when applying the probes to the wires.

    I am tempted to disconnect this last speaker and try changing the blown fuse on my own amplifier again, to see if that is the problem, and came on line and found your site. Do you have any thoughts Marty?



    • Hi Nigel. It does sound like you’ve narrowed it down very well, as 1 ohm is very, very suspicious. If you like you can test the speaker with a 1.5V battery (AAA, AA, C, etc.) and a bit of speaker wire. If it’s working there will be a little popping noise from the speaker when you momentarily touch the battery to the wire.

      However at this point it strongly seems like it’s that particular speaker. Before trying the amp again I would open up the speaker if possible and look into where the issue is and go from there. Ideally you should be able to remove the speaker driver(s) and measure resistance right at the terminals. It could also be an issue with the speaker crossover.

      It sounds a lot like you nearly have a short in it somewhere so I think it’s worth opening it up and looking further. You can use the 2nd speaker like it for comparison when narrowing down the cause. Hopefully that helps!

  3. Hi! I have a 16ohm vintage horn compression driver that measures 7.5ohm with a digital multimeter. Should I be concerned that it reads less than half of the written impedance?

    • Hi Mikkel, how are you? Hmm, 7.5Ω is a bit low for what is supposedly a 16Ω rated horn, but that’s not necessarily a red flag. If it’s a standard magnet & voice coil type of horn driver the DC resistance measured across the voice coil can be low.

      If it plays and works fine it’s mostly likely closer to actually being an 8Ω driver and not 16Ω after all. If you have a 2nd one to compare it to I’d definitely do that.

      • Hi Marty! I’m good thank you, and thank you for your response. More specifically, the unit in question is a JBL 375 horn, so I’m positive that it is an 16Ω driver. I have a pair of matching horns and they both measure approximately 7.5Ω. However, I have seen another example online with similar readings for this exact horn model, so perhaps I shouldn’t be alarmed?

        • Hi Mikkel. I think I see what is probably going on here. It sounds like the 8Ω voice coil diaphram is in the ones you have instead of the 16Ω option. It sounds to me like someone changed them.

          There’s a guy currently with a pair on eBay measuring almost 8Ω also (item #294411342752). In the listing they also mention: “Both diaphragms appear to be original JBL, but possibly from different eras which may explain the slightly different ohm readings shown.

          Best regards.

  4. How does the little switch on my crossovers being used on Audison component speakers that allows for settings of 0 db or 2 db effect the function/output of the speaker?

    • Hi David. The 0dB setting is usually a pass-through while the other setting(s) reduce the output to the tweeter/speaker itself. It depends on the particular design of the speaker crossover being used, but generally power resistors are used to reduce the output to the speaker, similar to an L-pad or attenuation network.

      Ideally, it should have no affect aside from reducing the voltage/power to the speaker and nothing else – at least not anything noteworthy.

  5. Marty, I have a Kenwood amp KA-9100 and I want to run 4 speakers. I hooked them up on my A/B speaker connections. All speakers are rated at 8 ohms. I was told that it would be ok to run one wire per channel and hook the speakers up in series on each side. Is this ok? I am looking for the best possible sound. Is one way harder on the amp than the other?

    • Hi Doug. You don’t mention what type of speakers but I’ll assume they’re 2-way or 3-way, meaning they’re best used in parallel both for sound & power too. In the case of the Kenwood it handles down to 4Ω which means you can use the 8Ω speakers in parallel.

      In this case, you’d just wire one speaker per speaker output which is effectively wiring them in parallel. Wiring speakers in series is ok with single-cone speakers but not ideal for those with a crossover in use.

      Best regards!

  6. Hi Marty – I have a home loudspeaker all put together with first order crossover in place, and now realize there is 4.5 dB difference in efficiency between the tweeter and the mid (92 dB to 87.5 dB). I’d like to place an L-Pad (2 resistors) in front of the crossover so that I don’t have to change the components in the tweeter crossover. However, when I try to measure Re at the front of the crossover, I get 10092 ohms. Is there a way to determine the resistor values required, or should I just bite the bullet and install the L-Pad after the crossover and make the necessary changes in capacitor values?

    • Hi Ed. There’s an easy way to find out the resistor values you need. Since you’re looking for a non-typical dB attenuation amount (ex.: 4.5dB and not 3, 6, or whatever) you can just use my tweeter attenuation calculator here:

      That will make it easy. IIf you’ve been considering using an adjustable L-pad, the benefit is that they’re adjustable unlike a fixed resistor network. The downside is they cost more and you can’t be quite as exact in your design. Plus a resistor network takes up less space.

      Regarding what you measured (about 10KΩ), did you disconnect at least one speaker wire after the crossover before measuring resistance? If not the measured value will be affected by the crossover.

  7. Hi Marty. This is a amazing site you have here, I can’t believe it is current as well, not from like 5 years ago or something like that. Your article on speaker impedance is a great help as I’m thinking about a DIY project that is a bit tricky to figure out. I build speakers for a hobby, but I’ve always done projects that are designed by people who know what they are doing. I’ve also purchased surplus speakers that where made for high end TV’s for very cheap and used them in projects. I have two such Phillips speakers for computer sound and they are great. I’ve also purchased some Sony speakers that where designed for a $5k plasma TV, and I hooked them up to my TV’s 5.1 sound system. These where easy to use as they had two terminals and the impedance was known. I’m looking at some surplus Phillips TV speakers now however that have six wires. From what I understand, each one has two voice coils that are separated from each other and they are 16 ohms for each one. People are hooking up four of these modules in series and somehow wiring the group parallel to end up with a 4 ohm load. (this would make one speaker) The speakers are in a ported enclosure and they do have a crossover built in as well. I don’t have a wiring diagram from someone who has done this, just written text as part of their review of the product, so it will be a fun challenge for me. Anyways, the surplus speakers have a cost of $1.98 ea and I’m thinking of getting 16 of them to play around with.

    • Hello Arnie & I’m glad you like me site – thank you.

      There’s more than one way to wire an even number of speakers and get a given total Ohms load, such in this case. However, you won’t get a total of 4Ω by wiring all of the 16Ω voice coils in series-parallel. You can if you use only one coil per speaker or treat it as two groups of 4Ω voice coils all in parallel.

      If each unit has 6 wires that tells me there’s probably more information I need to help more. I can only somewhat “guess-timate” without better specifications for those.

      You can use my Ohms calculator to check your values if you like for doing it yourself: Best regards.

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