How to Test for Speaker Wire Polarity
It’s important that your speakers are wired to the right polarity to achieve the best sound quality possible, and obviously, failure to do so will produce lower quality sound that you've paid too much to deal with. 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. There are commercial devices that can check for speaker wire polarity, but using these steps, you can do it yourself without spending 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 guess work.
Take the speaker wires and wrap one around each of the terminals on the battery. Now, look at the speakers cones closely. The current from the battery will cause movement in them, and you'll will need to note how they move; the cone should go outward and then in. If it does this, the polarity is correct. However, if the movement is inward first, swap the wires around on the battery and look again. This time, it should be correct. These motions can be hard to distinguish immediately, so be vigilant and watch carefully.
Once you're sure of the proper polarities, use something like electrical tape to mark the wires properly. Then, you can reconnect them to the receiver, with the wire from the positive terminal on the battery going into the red terminal and the negative going to the black.
Step 4 - Try to Test With a Multimeter
If the movement test can't be conducted, you can use a multimeter test instead. Start by removing the speaker wires from both speaker and receiver. Then, set yourself up so one wire is wrapped around each terminal of the battery.
Set the multimeter to measure DC voltage, and touch the speaker wires to the probes. If your probe is touching a wire with an opposite polarity, such as the positive probe to a negative wire, you will get a negative numerical reading. Try switching which probe you're using to get a positive reading instead. This will allow you to mark which wire is which and reconnect them to your speakers properly.
Tip: You do need a current in order to measure with a multimeter, so having the battery is vital. You also need to be sure that you don’t measure from the receiver.
Listen to the speakers after you’ve established the correct polarity, and you’ll be able to readily hear the difference!