How To Tell If Your Car Speakers Are Blown

Your car stereo is one of those things that you take for granted until something goes horribly awry. When you get in your vehicle you expect to be able to turn it on and your favorite station or CD will start like it always does and sound good. If it doesn't go on or if what you hear is different than usual (in a bad way), maybe you have a blown or partially blown speaker. Let's investigate!

1. How a speaker works. This is the short version. A speaker consists of a circular magnet surrounding a coil that is attached to a cone-shaped diaphragm. Current goes through the coil of the speaker. Current is made, in this case, by an amplifier in your stereo. That current alternates at a frequency that is the same as the sound waves that generated it. That induces an alternating magnetic field in the coil. The polarity of the magnetic field of the coil switches positive to negative, so it is attracted to and repelled by the permanent magnet. The coil vibrates, then the cone vibrates and what you have is a facsimile of the original sound. 

2. How to tell if you speaker is blown by listening. Now, there are extremes of "blown" speakers. A totally blown speaker means that the cone has separated from the coil. The force of the sound wave "blows" them apart -- hence, the term. If this has happened, you will notice there is no sound at normal or low levels, or distorted buzz-like sounds at higher levels. Make sure, if you have an equalizer, that you put all the levels to "0" and the balance to the middle. This helps you to hear things better. If you hear music, but it is heavily distorted, then what you have is a partially blown speaker. This means that cone is pretty close to being totally separated from the coil. In all practicality, it pretty much means the same thing as if your speaker were totally blown. If you partially tear your Achilles tendon, you are just as injured as if you totally tear it. I should know, I'm a doctor. Not really. 
3. How to tell if your speaker is blown by testing. Get yourself an electric meter, like a multi meter they sell at your local Radio Shack. Set it to read ohms (impedance). Make sure your speaker is off and put one meter lead on each of the two terminals. If your speaker is blown, it will read infinite impedance. If your speaker is good to go, it will read 1.0. 
4. Test by feel. If you can't feel any vibration or thump coming from a subwoofer when the volume is up, it's probably blown. The big cones of woofers visibly move when the bass is turned up. Place your fingers lightly on it and turn the bass up. It's not the most reliable way to test them, but still another option you can try.

The best way you can tell if speakers are blown is using your ear. You know if it just does not sound right. Speakers are strange, sometimes lasting for decades of everyday use and sometimes blowing up with the first good blast of volume.