How to Test for Speaker Wire Polarity

An old stereo speaker with exposed speaker cones.
What You'll Need
Nine-volt battery
Electrical tape

When listening to a sound system with two or more speakers, it’s important that the speakers be wired to the right polarity because this affects the way they interact with each other and therefore greatly affects the quality of the sound coming out. Any given input signal applied to a speaker will cause it to move either "in" or "out" creating sound. If the input applied to several speakers wired with mixed polarity, it puts them "out of phase" with each other, meaning that while one speaker moves "in" the other move "out" and therefore create distortions in the resulting sound. The effect is much more noticed at the lower "Bass" frequencies. So, if you're having problems with getting good, clear sound out of your speakers, it's time to test whether mixed up wiring is the cause. Unless the equipment has been tampered with, it will be wired up with purpose speaker cable, with each of its wire identified with a marking or color throughout its full length. So the first thing is to verify that the wire connected to the receiver's red terminal is the same as the one connected to the red speaker terminal. The same goes for the black terminals and then the same process can be repeated for all speakers. If you're in doubt, there are commercial devices that can check for speaker wire polarity, but using the following steps will also let you achieve the same result without spending the extra money.

There are commercial devices that can check for speaker wire polarity, but using the following steps will enable you to do it yourself without spending the extra money.

Step 1 - Disconnect

Begin by unplugging your stereo system at the outlet. You should also remove any wires that connect the system to other devices, such as a television. Then, once you're sure power is completely off, disconnect the wires of one speaker from the receiver. You will also need to remove the cover on the front of the speaker so you can see the speaker cone.

Step 2 - Adjust to View Speaker Cone

You won’t always be able to see the speaker cones; not all covers are removable, which is particularly true with a subwoofer. If this is the case, you need to position the speaker so you can see through the grille to view the cones. It makes the task a little harder, but far from impossible.

Step 3 - Test With Your Battery

You will want a fully-charged nine-volt battery for this test, so just use a new battery to eliminate any guesswork.

The following steps should be repeated for each speaker. Take the 9-volts battery and connect the speaker's negative terminal to the speaker's black terminal. With this done, connect a wire to the red terminal on the speaker, touch it on the positive terminal of the battery. You'll notice the movement of the cone in the speaker. Keep doing the same to all of the speakers throughout your system making sure the cones in each and everyone moves exactly the same way. If one or some move in the opposite direction, you'll know that those have been altered internally, so the wires will need to be interchanged. These motions can be hard to distinguish immediately, so be vigilant and watch carefully.

Once you're sure of the proper polarities, you can reconnect them to the receiver, with the wire from the positive terminal going into the red terminal and the negative going to the black.

Listen to the speakers after you’ve established the correct polarity, and you’ll be able to readily hear the difference!