Diagnosing the problem with a vibrating speaker can be a stressful and time-consuming task, and is all the more difficult when you do not know what to look for. However, it is very important to diagnose your vibrating speaker correctly, as an incorrect diagnosis could cost you unnecessary amounts of time and money. Here are a few tips to make sure that you know the true reason that your speaker is misbehaving.
Locate the speaker that is vibrating by adjusting the balance and fade of your stereo receiver. Adjusting the balance will force the sound to come out of only the left or right speaker, and adjusting the fade will force the sound to come out of only the rear or front speaker, so you can test each individual speaker by adjusting both the fade and balance at the same time.
Check the mounting of the problematic speaker by holding the speaker in place while the speaker is in use. If the mounting is problematic, then the vibrating will stop once you begin holding the speaker in place. You can fix faulty mounting by tightening the screws which hold the speakers in place (for car audio speakers and home audio inwall speakers), or by making sure that the speaker is standing on a flat surface (for aerial home audio speakers).
Check to make sure that the problematic speaker's wall mounting (for home audio wall-mounted speakers) is not loose in the same fashion which you would check a car audio speaker by holding the mounting in place, and seeing if the vibration persists. Frequently, wall mounted speakers are secured with brackets that come loose at the connection between the speaker and the bracket. This can be fixed simply by tightening the bolts which hold the speaker in place.
Locate a blown speaker in the same fashion which you would locate a loosely mounted speaker, by adjusting the balance and fade of your stereo receiver to test each individual speaker. Remove any aesthetic coverings that hide the speaker from view (depending on the speaker, this could involve prying a speaker's grate off and/or unscrewing part of a car's panelling).
Look for tears in the outer cone of the speaker once its face is exposed. Typically, tears in the outer cone occur on the very outer rim of the speaker, and can vary in size between very small, almost unnoticeable fractures in the paper or rubber material to large holes or chunks missing from the speaker's outer rim. You can fix a small or large tear by covering the hole or tear with duct tape, making sure that the tear is as sealed as possible.
Remove the speaker from the housing or mounting which it is secured in. Depending on the type of speaker you are dealing with, this could involve unscrewing the speaker from the wall panelling of a car door, or removing a home audio aerial speaker from its boxed enclosure. Look for tears of the same nature as an outer cone tear, but on the inside of the reflexive cone, where the speaker's conical shape connects to the large magnet in the back of the speaker. You can fix a tear in this location just as you would an outer cone tear, applying duct tape over the tear until the hole is sufficiently sealed off.
A blown speaker can be temporarily fixed with duct tape, but it is always best to simply replace the speaker.