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

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!

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

Audio power resistor examples

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

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

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

For speaker systems, I recommend using one with a power rating of 25 watts or more to be sure. For car stereos (not car amplifiers – those are higher power), you can often get away with around 10W to 15W.

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

Resistors to avoid

Example of standard electronic axial resistor

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

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

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

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

How to add resistor to speaker to change impedance diagram

You can change speaker impedance with resistors for two situations:

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

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

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

1. Using resistors to increase the total speaker impedance load

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

To do so:

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

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

2. Using resistors to decrease the total speaker impedance load

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

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

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

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

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

Resistance in parallel is a little bit more complicated

How to calculate resistance impedance in parallel example diagram

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

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

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

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

How power is divided between speakers and resistors diagram

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

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

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

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

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

Overall power available is reduced for parallel resistors, also

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

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

Using resistors can sometimes slightly affect the sound

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

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

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

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

Example of power resistors in retail store on display hooks

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

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

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

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

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

Example of miscellaneous power resistors different values in package on floor

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

Where to buy resistors for changing speaker impedance load

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

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

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

How much do power resistors for use with speakers cost?

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

More excellent articles to read

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

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

Got questions or comments?

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Your comments are welcome!

  1. Hi,

    So, my head unit just sort of burned out or something because I raised the volume on a 4-8 ohms output head unit to speakers of 2 ohms and I’m guessing the easiest solution would be resetting that with 2 ohm resistors in-between. Do I just connect the resistors right between the head unit and speaker leads? I was a little bit confused about the crossover concept.

    Thank you very much for this article! It answered many of my questions.

    Reply
    • Hi Remy. Unfortunately, it’s likely that you permanently burned out the output transistors by using it with too low of an impedance load (speaker Ohms). I’ve got an article where I mention what happens in that case.

      The best thing to do is to first remove the head unit and test it to find out if the speaker outputs are working or not. You could also do this with it connected to the vehicle, but you’ll want to remove the speaker connections and use a 4-8Ω speaker to test each output channel one at a time.

      If you don’t have crossovers, the resistors go inline with the speakers. They add in series, like 2Ω resistor + 2Ω speaker = 4Ω total.

      Reply
      • Thank you so much!! It should be easy to just connect the resistors if it’s possibly not burned out. Wish I had read that article before but you’re appreciated brother!

        Reply
          • So I did add resistors to the head unit-speakers system and it worked out really great. The problem is that the head unit sometimes goes black/and the volume buttons don’t work at some point. I’m interested in your opinion on whether it may be due to the resistors or just the head units’ issue. It is refurbished with a warranty and before I send it in for a replacement, I want to make sure the problem is not on my side.

          • It’s been some time since we chatted here so I don’t recall the topic, but what you can do is to:
            – With the head unit turned off, remove at least one speaker wire for each pair and check the resistance with a test meter set to Ohms. You should measure at least 4Ω or higher (or very close to it).
            – Alternatively, you can test ala “bench test” style, either in or outside the vehicle. That is, with power connected, try using a test speaker to connect to one speaker output at a time under the same conditions.

            That should help narrow down if it’s the head unit having a problem or if it’s speaker/speaker load related. It shouldn’t go black or have the volume buttons completely fail to respond so I suspect it’s an issue with the head unit. When pushed to their maximum output, head units sometimes dim or flicker a bit but don’t normally go completely black.

  2. Hi dear
    My amplifier has an output of 10 W 8 ohm
    Can i put speakers one of 5w 8 ohm parallel with one 3w 8 ohm and then add a resistor of 4 ohm 2w serie with the two parallels

    Reply
    • Hi, yes that would work in general, but you’ll need a 5W resistor. When you have a 4Ω resistor in series with two 8Ω speakers in parallel, you’ll have 1/2 the amp output (5W) across it. The other speakers will have about 2.5W each available.

      Best regards.

      Reply
      • Thank you
        But if it will be 2.5 W on every speaker and the two speakers that i have are 5 W and 3 W, will they work normally on 2.5 W and will they give good sound?
        Thank you

        Reply
  3. Hi there sorry to be a pain. Im resiring a old pair of speakers and the wich have had different woofers put in they have 5ohms and the crossover is for 8ohms. So if i put 3 ohm a resistor between the woofer and crossover it will be crossed over at the correct frequency. That sed will i loose some of the higher frequencys with inductance from the resistor. Will I get a better sound using a 8 ohm speaker. I was thinking of replacing the unductor and cap but then the mismatch impedance will mean the woofer is to loud. Thank you for your indepth tutorial much appreciated.

    Reply
    • Hi Darren. There should be so little inductance in wire-wound resistors that it should be negligible. Otherwise, you can use a non-inductive type resistor if you like. Alternatively, you could use two 6Ω wirewound resistors in parallel to get the 3Ω but with 1/2 the inductance of using a single one.

      It shouldn’t really matter much using a 5Ω vs 8Ω aside from the frequency response differences and the volume drop you’ll have but that depends on the sensitivity of the 8Ω vs that of the 5Ω. Using a series 3 ohm resistor with the 5 ohm means you’ll lose a little bit under 3dB from the 5Ω speaker, but that’s almost too little to notice. Honestly, if possible the best thing to do is use an 8 ohm speaker and avoid these issues since 8 ohm speakers are very affordable and generally easy to find.

      Thanks for your feedback by the way. :)

      Reply
  4. Hello
    Sorry for disturbing but i have one question
    If I have an amplifier TPA3116D2 that has an output if the speaker was 4 ohm gives me 50 watts and if it was 8 ohm it gives me 30 watts
    I can connect a speaker that have a rated power 40 watts and the power handling capacity 80 watts (8 ohm) or what is the best thing to connect on it to give me the best sound?

    Reply
    • Hello Roger. I’m afraid I don’t quite understand your question as the rater power handling and power handling capacity are the same thing for a speaker. If the amplifier is 4Ω capable and you’d like the most available power from it, I’d use good quality 4Ω speakers instead of 8Ω. Both will work of course but the extra power would provide slightly more volume.

      Reply
  5. Hey there, I have 4 4ohm 6×9’s running on a 2 ch1000 watt, 4 ohm but 2 ohm stable amp, 2 6×9’s per channel wired parallel for a 2 ohm load per channel, when I wire up the 2-4 ohm two speakers in parallel, the load fluctuates to around 2 ohms and at times under 2 ohms? With both channels wired in, I get occasionally amp clipping, how and where can I add a resister to the load to keep the load above the 2 ohms to prevent the amp from clipping when the speakers are hitting on the deep end?

    Reply
    • Well, the first thing is that it’s extremely unlikely it’s actually a 1,000W amp. That sounds like the misleading “peak” power some amp companies use to sell products. The RMS or continuous power is likely much, much lower. The speakers will all have the power divided among them, which is probably contributing to the problem.

      I would try a 1/2 ohm resistor in series with each and see how it works out. 0.5Ω won’t be as bad as a larger value, as some power is always lost across resistors added in series with speakers. You can also try using the high pass crossover set to 50-60Hz, etc.

      Reply
  6. I have a Mark Levinson speaker system in a Lexus LS430, the subwoofer has gone bad (as apparently a lot of them do) The recommendation is to replace it with a Polk DB842DVC, a dual voice coil speaker, 4 ohms on each coil. The Amp is apparently 12 ohm, the recommendation is to wire the two coils in series to get to 8 ohms. Will putting that 8 ohm load on the 12 ohm amp cause it to eventually blowout as I have read some suggest? Or will putting the 8 ohm load on the 12 ohm not cause an issue?
    Thanks in Advance!

    Reply
    • Hello, Dennis. The answer is “maybe” it will cause issues with the amp. My initial impression is yes it would due to the increased current it would have to try and supply with a lower speaker Ohms rating. You could also wire a 4Ω resistor with a decent power rating (say 25W or higher) in series with the subwoofer to be 100% safe. The drawback is that you’d lose 1/3 the power across it.

      Alternatively, depending on the factory subwoofer you could see if you have have it repaired. I had a JBL subwoofer from an Avalon repaired (they dry-rot and deteriorate) which restored it to great condition. So it’s worth looking into.

      Reply
      • Thanks Marty! That was my thought as well that putting the resistor in line would make the load consistent with the AMP. I’ll consider doing that!
        Thanks again for your help!

        Reply
  7. OK my scenario is i have a 400 watt 4 channel amp that will push 80 watts at 4 ohms and 135 watts at 2 ohms. ( RMS ). I’m running 2 component sets ( 8 speakers mid and high with crossover ) that are 4 ohm sets. Can i bring the ohms down with resistors on the comp. sets before the crossover to get the higher wattage ?

    Reply

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