A blown subwoofer can be diagnosed by sound and by touch. A blown subwoofer may produce a fuzzy noise, a hissing noise or no sound at all. Partially blown subwoofers may produce a little sound at lower volumes and fail to produce sound at a higher volume. A base speaker that sounds as if there are rocks inside of it is likely totally or partially blown.
Subwoofers deliver base sounds and are larger than tweeters that deliver treble sounds. Some common causes for dispersed sounds include torn felt or fabric or a broken coil. If a visual inspection reveals torn fabric, the speaker can be easily repaired. If the speaker's coil is damaged, replacement is more cost-effective.
Subwoofers give off vibrations and when a speaker stops working, there is no power running through them. Touching the exterior of the speaker when audio volumes are high should produce a vibration on hands and fingertips. According to Cars Direct, "Turn the volume of your speaker system up and place your hand against the front padding of the speaker. If you feel any vibration, the speaker is creating sound. However, if you do not, it's likely that your larger speaker is not working properly."