Bass represents one of the driving forces of many types of music. Good bass reproduction enhances the musical experience, whether listening to it or creating it oneself. A vibrating woofer or subwoofer creates sounds that don't belong in the music, sapping the joy from the listening experience. In many cases, removing unwanted vibrations requires only a little work and then it's back to good vibes once again.
Hook up your sound system as you normally would and play the bass-heavy music loudly until the woofer rattles or vibrates.
Inspect the woofer's speaker cone. Is there a visible tear? If so, it needs replaced. If not, put your hand around the ring of the woofer as if holding it to the speaker cabinet. Does this stop the rattle? If so, padding is needed between the woofer and the cabinet. (Proceed to the padding section.)
Inspect the face of the woofer cabinet for loose parts. Are any screws loose? Is the speaker housing loose? Search closely for any visibly loose parts. Is the cabinet itself the problem?
Tighten any loose screws discovered in Step 3. If the cabinet itself is the source of the problem, add more screws to tighten the box.
Test the woofer again by playing loud music. If it still vibrates, proceed to the "padding" section. If not, problem solved!
Locate the screws holding the woofer into place and unscrew them. Place the screws somewhere safe.
Pull the speaker out of the cabinet. Disconnect the wires connecting to the speaker. Do this only if the wires are easily removed. If not, work around them.
Trace the outer circle of the woofer onto the paper. Cut out the circle.
Trace the paper circle onto the cardboard or foam.
Cut out the circle of foam or cardboard. Draw a rough circle inside this circle, approximately half an inch from the outer edge of the foam or cardboard.
Cut out the area inside the inner circle, resulting in a ring of cardboard or foam. Slide this over the back of the woofer so it lies flat against the backside of the ring around the subwoofer. (Cut a slit in the foam or cardboard if the speaker wires are still attached, to slide it over the woofer.)
Place the woofer back into the housing. Put the screws back into place.
Retest the woofer by playing loud music through the speakers. Repeat any steps as necessary if the vibration is not gone.
If you cannot locate the source of the buzz, play several different songs, all with heavy bass, through your sound system. Perhaps the music itself is the culprit. If you have two of the same woofer cabinets, swap the speakers to see if the problem replicates. This helps determine whether the vibration is fixable or if a driver or the cone itself needs replaced.
Be careful not to puncture the speaker cone while working as it would render the speaker useless.