How to Determine a Speaker's Ohms

Use a multimeter to measure the impedance of your speakers.

All electronic components have electrical resistance call "impedance." Impedance is measured in units called Ohms after George Simon Ohm. Speakers typically come in three different impedance ratings: 4 ohms, 8 ohms and 16 ohms. The impedance of the speaker you need depends upon the output impedance of your amplifier and the number and configuration of speakers you connect to that amplifier.

Things You'll Need

• Multimeter (digital or analog)

Instructions

1. Look on the back of the speaker where the wires connect. There should be a sticker or stamp with various information printed on it, including the impedance of the speaker.

2. Set your multimeter to the lowest numerical "Ohms" setting, usually 200. It may not be labeled "Ohms. It may have the Greek letter "Omega," which is the symbol for ohms and resembles a horseshoe or a small pair of headphones. The settings are typically 2000K, 200K, 20K, 2000, 200 and Diode checker, which is a sideways triangle with a vertical line at its tip and a horizontal line through the middle of the symbol.

3. Touch the negative, black, test lead to the negative terminal on the speaker, and the positive test lead, red, to the positive terminal on the speaker.

4. Watch the multimeter's screen. If you are using an analog meter, the needle will hold approximately at 4, 8 or 16 depending on the speaker's impedance. On a digital multimeter you will get a numerical reading on the LCD screen.

Tips & Warnings

• The impedance of the speaker will change over time, and is never exact. You might get a reading of 7.5 up to 8.5 for an 8-ohm speaker.

• If you have an impedance mismatch between your amplifier and speakers, you risk damaging your amplifier and/or sacrificing the speaker's sound quality.

• If you are running more than one speaker from a single output, keep in mind that every speaker you add will drop the impedance in half. For example, if you have two 8-ohm speakers on the same amplifier output, the combined speakers result in an impedance of 4 ohms.

References

• Preston Electronics, LLC: Meditations on Speaker Impedance ("OHMmmmmmmmm")