As a speaker that emanates low bass frequencies, your subwoofer is vital in creating a full sound when you're listening to music. So when you detect a noticeable lack of bass in your subwoofer, it's likely that either the voice coil is damaged, or that something has gone wrong with the speaker cone, resulting in a blown speaker. A few simple tests can determine whether there's a problem with your subwoofer.
Test For a Blown Coil
A voice coil is a piece of wire that attaches to the speaker cone and amplifies the current that runs to the speaker. Voice coils typically have two terminals, positive and negative. To test whether a voice coil is blown, obtain a multimeter, a device that tests the amount of voltage, resistance and current. Turn the speaker off and remove the coil from the positive and negative terminals. Attach the positive and negative multimeter probes to the positive and negative terminals. The multimeter is used to determine whether there's any electrical resistance in the coil circuit. Resistance in electric circuits is measured in ohms. Complete lack of electrical resistance will mean that your coils are damaged. Any reading above 1.0 ohms indicates that the coils are not blown. Readings below 1.0 ohms, or readings that shift abruptly from one ohm to another are a strong indication that your coils are blown.
Test the Cone
Remove the cover off the subwoofer to reveal the cone. Gently push on either side of the cone to determine if the cone moves or if it remains solid. A subwoofer is built with a suspension system that allows the cone to move. If the cone doesn't move at all, something has definitely gone wrong with the components of your subwoofer.
Test the Sound
A blown subwoofer is detectable by the quality of sound that is produced through the speakers. Turn on your sound system, ensuring that the volume is low, at first. If there is sound but it is very distorted, this means that your subwoofer is partially blown. If there is no sound, or all you hear is static or a persistent buzzing, especially with the volume turned high, this is a strong indication that your subwoofer is completely blown.