On their own, egg cartons do not provide complete soundproofing. But their unique shape makes them a valuable tool as part of a larger soundproofing process. As sound waves travel through space and reflect off surfaces in your room, the many turns and grooves in the bottom of an egg carton deflect sound vibrations, helping to absorb them and reduce noise.
Choose cartons made from Styrene or paper fibres rather than plastic. Styrene and paper are porous and soft and will better absorb sound. Measure the room's walls to find the square footage--don't forget to measure the door, as well.
Attach a soft layer of sound-absorbing material to the walls. Depending on your budget, and whether your soundproofing is permanent, you can use soundproofing foam, foam rubber or household materials such as lengths of cloth, thick blankets or mattress padding. Attach these with nails and glue, if permanent, or mounting tape, if temporary.
Prepare the egg cartons. Check them for any egg shells or residue. Remove shells and wash away residue with soap and water if using Styrene cartons. With paper cartons, cut away marred segments with scissors. Cut off the tops of the cartons and discard.
Stuff the insides of the cartons with soft materials such as wadded-up newspaper or cotton stuffing. Secure the stuffing with tape. This will create extra sound absorption.
Create hanging flaps on each carton bottom using duct tape. Attach a strip of tape to each of the four edges of each carton. Fold the tape over itself to cover the sticky side.
Hang the cartons on the wall. Use staples to attach the tape flaps to the soft materials on your wall. Line up the cartons edge-to-edge with the round--bottom--sides out. Attach each carton separately rather than attaching them to each other. This is more structurally secure.