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 car speaker. If you do need to replace your car stereo speakers, then I strongly recommend you pick up a copy of Secrets of a Professional Installer to learn how to switch out your old speakers with new ones.
Let's investigate your car audio system to see if you have any blown speakers!
- How a speaker works. This is the short version. A car 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 and 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.
- How to tell if you speaker is blown by listening. There are different degrees of "blown" car 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 will help you hear any distortions in the sound. If you hear music but it is heavily distorted, then what you have is a partially blown speaker. This means that the 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 and it should be repaired.
- How to tell if your speaker is blown by testing. Get yourself an electric meter - for example one of the multi-meters 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 isn't damaged at all, it will read 1.0.
- Test by feel. If you can't feel any vibration or thump coming from a subwoofer when the volume is up, your speaker is probably damaged. The big cones of car audio subwoofers 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 to know whether your car's stereo speakers have a problem is by using your ear; distorted sounds or the buzz of the cone vibrating against the coil are the best indicators that it's time to replace your speakers. Your mechanic or a good car stereo shop will be able to do the job for you.