How to Test Ohm Load with a Voltmeter

What You'll Need
An analog or digital voltmeter
A speaker cable to test

If you would like to test the ohms load, or impedance, you may be able to use a voltmeter to quickly accomplish the task. The Ohms measurement is used to represent the impedance, or resistance, of a circuit when voltage is applied to a device with a pulsating or alternating current.

Headphones, speakers and other audio or video equipment often have impedance ratings, and you should know how to determine the rating on a piece of equipment. Although there are times when other expensive test equipment will be needed to measure the ohm load on certain devices, there are times when you can use just the voltmeter to achieve the task.

A good example would be when testing a speaker cable for resistance or impedance. You can also use the same test to see if a speaker cable is damaged or broken. This handy step by step guide will show you how.

Step 1 - Turn Off All Stereo Equipment

Before you begin, ensure that all of the stereo equipment is turned off in order to avoid causing shorts or other damage to the equipment while you are testing the speaker cable.

Step 2 - Disconnect Cable from Speakers

Remove the speaker cable from the speaker box by removing the individual wires from the connectors.

Step 3 - Disconnect Speaker Cable from Stereo Unit

Likewise, you'll need to remove both speaker wires from the stereo amplifier or receiver unit. Be careful when removing the wires, and be sure to fully disengage the wire connectors or locks before attempting to remove the speaker cable.

Step 4 - Connect Cable at One End

Take one end of the speaker cable and twist both of the bare wires together lightly. Be sure not to twist them too tightly as this may make them difficult to separate or even cause damage to the speaker cable.

Step 5 - Set Up the Voltmeter

Insert the test probe leads into the voltmeter. When inserting the probe leads, insert them in the spots marked for ohms or resistance testing. Some voltmeters may have an Omega sign or symbol that indicates the plug-in port used when testing for impedance or ohms resistance. Then, turn the voltmeter on and turn the selector switch to the ohms or resistance setting.

Step 6 - Test the Voltmeter

Test the accuracy of the voltmeter by touching the red and black probe leads together. If the voltmeter is functioning properly, the display should show a result of zero on a digital voltmeter and should display infinite ohms on an analog meter.

Step 7 - Test the Impedance of the Speaker Wire

Touch the black and red probe leads to the exposed wires at the open end of the circuit (or the end of the wire that is not twisted together). If the speaker cable is not frayed or broken, the resulting resistance that is displayed on the voltmeter will be the impedance or ohm load for the speaker cable. In most cases, the ohms reading displayed should be between about 2 to 8 ohms.