The foam ring that surrounds the speaker cone in a home speaker -- also known as the "surround" -- is a vital part of the speaker mechanism. The surround supports the speaker cone as it moves back and forth, allowing the cone of the speaker to accurately turn the electrical impulses of the speaker motor into sound. Foam surrounds can deteriorate over time, and a broken or rotted surround will cause a buzzing sound in your speaker, in addition to failing to support the cone properly as it moves. A broken surround can be fixed on many speakers.
Purchase a speaker surround repair kit. These are available for a wide variety of speakers from many online sources. An example is listed in Resources. Be sure to buy a kit that is specific to your brand and model of speaker.
Lay your speaker on its back and remove the cloth grille. These are usually held on with Velcro or push-type fasteners and simply pull off. Some other speakers may hold the cloth grille on with staples in the corners.
Unscrew the screws on the perimeter of the speaker and pull it out of the speaker cabinet. Unplug the speaker wires attached to the back of the speaker. Pull off the remaining foam surround and glue from the edge of the speaker cone. Use the sharp edge of a knife and rubbing alcohol and a rag to remove any stubborn spots of glue or foam.
Apply a thin layer of glue -- supplied with the repair kit -- onto the edge of the speaker cone and the underside of the new surround. Slide the surround onto the speaker cone and position it so it is centred. Let the glue dry according to the instructions in your speaker repair kit.
Plug the speaker back into the speaker wires in the cabinet. Replace the speaker in the cabinet.