Your Guide to Measuring the Impedance on Speakers with Ease

The impedance of a speaker can be tested using an Ohmmeter or Multimeter

Some of our customers are beginner audio enthusiasts who may only have a multimeter and no professional measuring equipment. They want to know if they can use their existing tools to determine a speaker's impedance roughly. For instance, they might want to check if the speaker's nominal 8 Ohm rating is correct or if there is an issue like a short or open circuit.

It's important to understand that a multimeter measures Direct Current Resistance (DCR), while a speaker's nominal impedance refers to its Alternating Current (AC) impedance.

Photo taken by one of our Quality Control Technicians of a 4 Ohm Woofer.

This nominal impedance is typically the minimum or average value at a particular frequency. There is a general relationship between DCR and nominal impedance, where the DCR is usually about 60-90% of the nominal value. For instance, for an 8 Ohm speaker, the DCR might be somewhere around 5, 6, or 7 Ohms. Although a multimeter cannot measure AC impedance directly, you can still use it to roughly estimate whether the nominal impedance is reasonable based on the DCR.

• For a speaker with a nominal 4 Ohms, the DCR is about 2.4 to 3.7 Ohms;

• For a speaker with a nominal 8 Ohms, the DCR is about 5 to 7.7 Ohms.

The data provided should be used only as a rough reference.

Measuring the impedance of a speaker is not a straightforward task, as it involves more than just assessing a single speaker unit. Inside the speaker is a crossover network, and multiple speaker units may be connected in parallel or series configurations. As a result, the Direct Current Resistance (DCR) measured with a multimeter becomes more complex. The inductor and capacitor in the crossover will behave differently under DC conditions; the inductor will act almost like a short circuit, while the capacitor will behave like an open circuit. Therefore, when measuring the DCR of a speaker, you can only measure the DC resistance of the woofer. The tweeter may, or may not yield any measurement due to being blocked by the crossover capacitor.

It should be noted that the speaker's impedance changes with frequency. The multimeter can only measure static resistance and cannot display the impedance curve or resonant frequency.

If you need a precise impedance curve, you'll still need special equipment, but a multimeter is a good choice for quickly checking whether there's an open or short circuit.

Resistance close to 0 Ohms: the voice coil may be short-circuited, or the crossover may be short-circuited.

Resistance infinite: the voice coil is broken, the crossover is damaged, or the wiring is disconnected.

Summary

Measuring Resistance: You can use a multimeter to measure DC resistance, which can help determine whether the speaker is functioning normally or estimate its nominal impedance. However, this method does not provide the AC impedance curve or the exact nominal value.

Safety Tips: Always disconnect the speaker from the amplifier before taking measurements to prevent any potential damage to the equipment. For a more straightforward approach to measuring impedance, we recommend carefully removing the driver(s) from the speaker and measure it outside of the speaker cabinet.

A multimeter is sufficient for a preliminary inspection, but special instruments are necessary for professional debugging.

That's all for this time. We hope you have a great time!

Welcome to our "Aperion University" series. Here, we will introduce you to basic acoustics knowledge. We hope it will help you. If you like it, please follow us!

Note: The images in this article are obtained from the Internet. If there are any issues, please contact us for removal.

Sign up for our newsletter below, and join our social media groups to stay updated with the latest news and information from us at Aperion Audio! You can also listen to this in video form