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. As long as the speaker impedance is equal or higher than a stereo or amp’s minimum Ohms rating it will work safely.

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.

Your comments are welcome!

  1. I found a 16 ohm mid driver in a 4 ohm speaker. It had a 4.7 ohm resistor in parallel resulting in a 3.63 ohm load. What I do not get is why the volume of the mid driver would still be correct. The driver is still 16 ohm, the amp is just burning more power that doesn’t get converted to sound where normally with a 4 ohm mid all would be converted to sound. So the mid section would not be in line anymore with the bass and tweeters.

    Reply
    • Hi Marc. That’s correct, for normal 3-way speaker system the volume of the mid driver in this case will not be correct at all. And like you said, it won’t be in line with the tweeter and woofer. The 4 ohm speakers will develop power at a way different rate than the 16Ω as the volume is increased.

      The parallel resistor will help keep it close to the 4 ohms expected by the crossover so the crossover’s behavior doesn’t change much, although yes it will consumer power also (wasted as heat).

      Without more information there’s no way to know why a 16 ohm would be used in place of a 4 ohm speaker. My guess is someone didn’t have a 4 ohm driver or didn’t care enough to get the correct speaker impedance.

      Reply
      • Thanks for your answer Marty, I fear you are right. I thought the speakers sounded very receded in the mid range and blamed the old capacitors (it’s from the seventies) . I will have to look for some 4 ohm mid range speakers.

        Reply
  2. Marty, thanks for an excellent explanation of both the how-to and possible-cons of such an endeavor. I’m a mechanical engineer, but even I could understand the electrical side of this, and the visuals help a lot!

    I’m just getting into custom building home hi-fi, and have a couple midranges I wanted to use with current x-overs that are the wrong impedance. I was going to spend quite a bit to buy the 8-ohm version of the same speaker (because other than wrong imp. I like their sound a lot), but I’ll try this first, see if it fits the bill for the time being.

    Reply
    • Hi Tom. Thanks for taking the time to write a comment and to let me know what it helped you. I appreciate it!

      That sounds like a good plan; as I often say it’s worth trying it out to see that you think. After all, whatever makes you happy and works for your is what’s best after all, no?

      Best regards. :)

      Reply
  3. I am looking at buying a home theater system but the speakers I have are 6ohm and the theater system is 8ohm what would you suggest.

    Reply
    • Hi, you’re going to have limited options. Personally I would suggest getting one that’s 6Ω capable or you may be able to use a speaker impedance adapter to match them the the 8 ohm system.

      Reply
    • Hi, I believe that should work fine. I’m not sure how much of an influence the cone would have (if still there) on the impedance but it should still have approximately the rated impedance as specified.

      Reply
  4. Am trying to figure out how to run 6 speakers(3 different pairs) to a standard Walmart CD player with 2 channel output. I can got 3 per side or 2 and 4 due to room size etc. The issues:

    •Don’t know Ω etc for the built-in amp, but 1 pr of the speakers came with it and they’re 4Ω, so I assume that to be the min resistance per channel.
    •Dont know the W of the built-in amp either, but the power supply is 5v 2.3a, so…11.5W safe guess?..it is a CD player not just an amp. The speakers show no W either just ohms.
    •Second pair of speakers are 8Ω 3W
    •Third pair are 8Ω 9W, and if I hook one of those up with 1 of either other pair, either in parallel via a Ycable or 1 per channel, the 9W is significantly quieter.

    I was planning to do the same on each channel, with the splitter hooked to one of the 8Ω and a series of the 4Ω and other 8Ω. That would give me 8Ω and 12Ω in parallel for a total of 4.8Ω. However now that I see how big the volume difference, I’m not sure what’s best to equalize volumes across all 6 speakers. The other option would be to parallel the 2 9Ws on one channel, and then parallel 2 series of the 4Ω and 3W 8Ω on the other channel.

    Since idk the W nor Ω of the amp nor the W of the 4Ω speakers, only that the 9W speakers are considerably quieter than the others unless I do a 9W on one channel and any pair of the others on the Y on the other channel, I’m tryin to figure how best to balance them. The little speakers that came with it are only 4′ wires, and the other 4 speakers are 9-10′ wires in old wood cases w brown wires, all stated equipment from yardsales (8Ω speakers all free) so I have no real info and I want to kinda surround sound a room of about 18*14′, for music only not tv. I can put the source in the middle or offcenter as needed, and all speakers will be on the floor(carpeted) along walls.

    My first plan was to use Y splitter between the 4Ω and an 8Ω then wire the other 8Ω in series with the 4Ω, same on both channels. But, due to W difference and volume disparity, should I do that but put the 9W on the parallels and the 3W on the series? OR should I put the 9Ws both in parallel on one channel only and run 2 series of 4Ω and 3W/8Ω in parallel on the other? OR, reading this, should I add resistors somewhere along the line like in parallel to the series’d 8Ω to make each half of the parallel 8 instead of 12?

    This is my first time messing with speakers that didn’t come with the stereo I’m hooking to, muchless wiring in series or parallel to hook 6 to 2 outputs, but I have experience with electronic circuitry itself and have access to an electrician in-house

    Reply
    • Hello there. Well, it’s asking a lot to use 3 pairs of speakers with that kind of stereo. It can be done, however, there’s no great way to do it. 2.67Ω is what you’ll have in all 3 sets in parallel which is too low for the stereo.

      – Wiring two pair in series will work but the total power to those will go down, then each will share a portion of that, so it’s not a great plan.
      – It can be made to work using series resistors but the tradeoff is they’ll consume part of the power. And you don’t have much to begin with so that’s not practical.

      Realistically this isn’t very feasible. Using more than 2 pairs of speakers is always difficult, especially with mixed Ohms ratings. One option is to connect the stereo to an external amp so you’ll have decent power to drive multiple speakers.

      If you don’t want to spend money the best way is just to wire the 4Ω in series with the 8Ω and then those in parallel with the other 8Ω. It’s not going to be good but all things considered it’s probably the best way without adding an external amp or receiver. You could get pretty good sound using an external amp or receiver if the stereo has RCA (line out) jacks.

      Best regards.

      Reply
    • As a side note, if you want to follow up later and let me know how it goes & how the sound turns out for you I’ll try to help you the best I can. Have a good weekend! :)

      Reply

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