What Happens If I Use A Different Impedance Speaker On A Crossover? Can I?

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.

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.

diagram showing how a 2-way speaker crossover works

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.

Additional reading to see

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Check out my full line of how-to & info articles here.

Your comments are welcome!

  1. Hi Marty,
    I have a question.
    I have a Kenwood head unit which outputs 50w x 4ch @ 4 Ohms each.

    I currently have 4 cross-over kits installed. One per channel.

    They are also Kenwood. Each kit consists of a 6.5″ midrange speaker, a crossover and a tweeter.

    I have four larger tweeters lying around. Each of the four tweeters has its own high pass filter(the seperate box type).

    What would be the best way to connect these extra tweeters into my existing system?

    I initially thought two tweeters per channel front L and R and two crossover kits per channel rear L and R.

    Please let me know what you think.

    Thank you in advance and excellent articles!

    Cheers,
    William.

    Reply
    • Hi William & I’m glad you like my site! Regarding your questions:

      • The Kenwood (unless it’s a higher power unit) is likely rated at “peak” watts. Head units with average power have only about 15-18W/channel RMS available. I know there are some head units with a bit more power these days (better internal amplifier).

      • You can’t wire the additional tweeters to the existing crossovers without problems (crossover shift as it’s called).

      So you’d ultimately be better off either getting a small 2-channel amp or even better, just driving all speakers with a decent 4 channel amp at least. That’ll eliminate the speaker load (Ohms) problem and also deliver better sound as well.

      There are some ultra-compact amps these days that can fit in a dashboard in fact if space is an issue. Ideally you’d use an amplifier when using component speakers anyhow in order to get the best sound from them. Plus more power to drive them a bit hard when you want to.

      Reply
      • Thank you so much for your advice. I was thinking I wouldn’t be able to get away without an extra amplifier and now you’ve just confirmed it.

        I will start shopping around for another amplifier

        Thank you again. Your quick and sound advice(excuse the pun) is greatly appreciated in today’s messy Internet world.

        Kind regards,
        William.

        Reply
  2. A friend rebuilt my crossover, and we changed the tweeters in series resistor from 2.5 ohm to 3.9, to drop it a couple dB. It is a 4 ohm tweeter, so total tweeter resistance went from 6.5 to 7.9 ohm. The high pass crossover for the tweeter was at 3 KHz. I am trying to figure out what it is now.

    Reply
    • Hi, as the crossover frequency is inversely proportional to the load impedance, I estimate it’s around 2.5KHz now. You can find out exactly if you calculate it yourself if you know the capacitor and inductor values (if applicable). But 2.5KHz should be about right.

      Reply
  3. Hi Marty, it’s me again.
    I need some further advice please.

    I finally installed an amplifier in my car to power the tweeters as mentioned in my first question.

    Should I use the little filter boxes that came with the tweeters and set the amplifier to FULL or High Pass Filter?

    OR

    Should I leave out the filter boxes and set the amplifier to High Pass Filter?

    I know it will work either way but I’d like your opinion on what you think would be/sound the best?

    Kind regards,
    William.

    Reply
    • Hello William. Do you know if they’re 6 dB/octave or 12dB/octave (2nd order) crossovers? If they’re 6dB they’re probably fine but yeah 12dB is better. If they’re 6dB you could use the amplifier’s built-in high pass crossover instead (these are 12dB or better), but most amps don’t have a crossover frequency adjustment that goes that high.

      Honestly, I don’t think you’re likely to hear any difference in sound quality unless there’s more going on. It also usually matters more the type & quality of the tweeters practically speaking.

      Long story short, you’re generally fine leaving the amp channels set to full range and just using the included tweeter crossovers. That’s especially true if you may want to add other full range or mid speakers in parallel with the tweeters on the same amp channels later on.

      Best regards!

      Reply
  4. Hi Marty,
    Unfortunately, I don’t have details for the filter boxes. They’re unmarked.
    I will leave them out for now and set the amplifier to HPF.
    I will keep them though in case I want to add full range speakers in the future.

    Once again, thank you for such a fast and detailed response.

    Kind regards,
    William.

    Reply

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