In this post, we will dive a little bit into the most asked about speaker specification (besides power ratings) and that is impedance. Whether it’s printed in the manual, or listed on the back of the speaker or subwoofer, impedance is something that will need to be taken into consideration at some point when building your car audio system. 

What Exactly Is Impedance?

In any electrical circuit, there will always be some sort of resistance to the flow of current through the circuit, and car audio is no exception. The impedance of a loudspeaker, or subwoofer, is the AC (alternating current) resistance, measured in ohms (Ω) of the speaker or subwoofer voice coil. The higher the measurement in ohms, the more resistance or load is put on the amplifier. The lower the impedance, the less resistance or load will be put on your amplifier. This measurement will be important later on when choosing an amplifier that will best match the speakers or subwoofers you may have in your car audio system.

Why Is The Impedance Important?

Impedance is a very important value to consider when choosing an amplifier for your system. This specification will help you to determine how to best match the power output of your amplifier to the power ratings of your speakers or subwoofers. For example, you may have a subwoofer that is measured at 2 ohms and has an RMS rating of 500 watts. In this case, you will want to look at amplifiers that will output your subwoofer’s RMS-rated power at a load of 2 ohms. This will allow your amplifier and your subwoofer to perform at their best. 

Can A Subwoofer’s Impedance Be Changed?

Simply put, yes, but only if it has been built to. Take a single 12” subwoofer with a single 4-ohm voice coil. In this case, the subwoofer’s impedance cannot be changed because there is only one voice coil and how that subwoofer can be wired is limited to one way. Now, on the other hand, if you had a similar subwoofer, but in a dual-voice coil configuration, you would be able to wire that subwoofer in various ways to change the final impedance of the subwoofer. For instance, if the subwoofer was a dual 2-ohm voice coil configuration, you would be able to change the impedance to either a final load of 1 ohm or 4 ohms depending on if the subwoofer has been wired in series or parallel. Changing a subwoofer’s impedance gives the user greater flexibility when choosing an amplifier and matching car audio components.

Does Impedance Affect Sound Quality?

There is no correlation between the impedance of a speaker or subwoofer and the quality of sound they can produce. As stated previously in this post, the impedance of the loudspeaker will only affect the output of the amplifier to the speaker’s voice coil.

What if I Use The Wrong Impedance?

Typically, raising the impedance of a speaker may not have a negative effect on the amplifier itself, but it will lower the power output of the amplifier, sometimes drastically. On the other hand, lowering the impedance of the speaker below the minimum specified by the amplifier’s manufacturer can result in increased power output, but will also cause the amplifier to overheat and potentially fail. 

How To Measure A Speaker’s Impedance

If you are uncertain of your subwoofer or speaker’s impedance, there is a quick and easy way to check this. You should check the impedance regardless, just to ensure the speaker or subwoofer is, and will, function correctly.

In order to check the impedance of a speaker, you will first need a multimeter that can read resistance. Set the multimeter to the resistance setting (usually marked as Ω). Once set to the proper setting, touch the probes of the multimeter to the terminals on the speaker. The impedance of the voice coil should be displayed on the display. For example, if the speaker is labeled as a 4-ohm speaker, the multimeter should read somewhere in the 4.0 to 4.3 range. If the speaker or subwoofer is a dual voice coil, make sure to check both coils to ensure that both impedances match. If not, one of the coils is possibly bad.


I hope this quick post has given you a little more insight and understanding into speaker impedance and its role in car audio system building. If you are interested in how to change the wiring of your speakers or subwoofers, you can find some more information in my previous post about that subject, here.

If you have any comments, or if you think I have missed anything, leave a comment on this post and share your thoughts.

About The Author Brandon L

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