A common problem that occurs both in car and home audio systems is tearing or ripping of a speaker cone. This is caused when music is played too loudly for a long period of time, or just due to the passage of time--your speaker cone may get dry and simply crack on its own. Sometimes the tear or rip is so severe that simple repair methods will not fix the problem and you will have to take off the old cone and replace it with a new one.
Purchase new speaker cones and gaskets. You can sometimes find whole kits that include all the pieces you will need to replace the cone of your speaker at local electronics stores or music shops. You might also want to check on the Internet for music shops that sell cones and gaskets. eBay is a great place to look for some deals on cone kits; Recone Kits is a great site to visit as well (see Resources below).
Take apart the damaged speaker. Take your knife and cut around the edge of the cone. Peel it back and pull it off of the speaker.
Stick the blade of your knife between the gasket and the inside part of the speaker. Pop out the old gasket and throw it away.
Clean the old glue from the speaker frame. Use your knife to scrape away as much of the glue as possible. Apply some type of glue solvent or remover and wipe away the rest of the dried glue from the frame.
Cut a piece of your index card about 2 inches wide and slide it in the voice coil gap. Once you have the index card piece in place, secure it with a piece of masking tape. This piece will be used to help make sure that your new replacement cone will fit properly into your speaker frame.
Apply glue to the speaker frame. Put the new replacement cone onto the frame and the glue. Allow the glue to dry for a day or two before moving on.
Take out the index card piece and attach the new gasket on to the speaker. Apply some glue to the area around the voice coil of the speaker and attach the dust cap that came with your kit.
Solder the wires to the wire terminals. Reassemble your speaker and test it to make sure it is working properly.