Applying Egg crate to a wall will provide soundproofing. Not only will this not provide adequate soundproofing, but it may actually provide the opposite effect, resulting in enhanced sound.
Sheets of foam rubber that are attached to a wall will eliminate sound. The problem with this concept is that common foam rubber actually costs about the same as many legitimate soundproofing materials, only it crumbles over time, which causes a mess and removes any soundproofing characteristics that may once have existed.
You can soundproof a wall by nailing mattresses to its surface. In order for this to be effective, you’d need to make sure that all spaces were eliminated between them and thoroughly caulk the edges – even the tiniest gap would compromise the integrity of the soundproofing. Afterward, you’d face the possibility of mold – which would emit an odor – as well as the possibility of mice turning it into a rodent condo.
Fiberglass insulation is a good soundproofing agent. You need to remember that this is meant for the purposes of insulating a room, and not for soundproofing and, as a result, does very little to block sound from entering or exiting a room.
Plywood panels or particle boards that are nailed to the walls will soundproof a room. The fact of the matter is that wood will only help the sound to resonate, rather than provide soundproofing. Due to its non-absorbent surface, sound will bounce off of it and may actually increase the amount of noise within the room.
Nailing carpeting to the wall will help to reduce noise. If you remember that sound absorption and sound reduction are two entirely difference concepts, then you’ll understand that, while the carpeting will help to absorb the sound (ridding yourself of echoing within the room), it does nothing to actually block the sound.