How to tell if a subwoofer is blown?
A subwoofer produces the heavy bass sound for your system, be it a car stereo or home theatre. A sudden power surge or prolonged high volume can damage the vibrating coil inside the cabinet and possibly split or rupture the round speaker cone that delivers the low-frequency bass sound.
Before replacing a subwoofer, particularly an expensive component such as a powered subwoofer used for home theatre setups, it's a good idea to test the equipment and determine if it is blown or if a minor repair could get the bass blasting again for minimal expense. A mid-range subwoofer for home use can be pricey, but a minor rupture in the speaker cone can often be fixed for the price of an inexpensive tube of sealant available at electronics stores.
Remove the cover enclosure for the subwoofer by lifting it straight off.
Power up the system and adjust the volume no higher than medium.
Inspect the speaker cone for holes or rips. Special sealants are available at electronics stores to close a torn subwoofer cone that has a relatively minor split or has a hole from too much bass.
Gently depress the centre of the subwoofer cone, which is the centre piece surrounded by a large grey or black bowl (the subwoofer loudspeaker).
Listen for a distinctive scraping sound, which could mean a blown speaker coil inside the cabinet. This scraping or rattling sound typically means it's time to get a new subwoofer, because replacing a blown coil is almost as much as a new subwoofer. No sound or a persistent buzzing noise are common signs that the subwoofer is blown.
Test the subwoofer to see it if is getting power and capable of producing any sound by connecting the two speaker wires off the subwoofer to the terminals of a 9-volt transistor battery. If the subwoofer is working at all, you will hear a brief popping sound and the cone will push outward.