In order to buffer sound and reduce echos, recording studios and home musicians often attach acoustic foam to the walls of a room. While not exclusive to use by musicians, this material is immensely useful to people looking to reduce echos in a room or prevent excess noise frequencies from escaping to the outside of the room. Conversely, it can keep outside noises from coming into a room. It comes in a variety of sizes, and is pliable enough to be nailed or otherwise attached to walls, ceilings, doors, and other features of a room to control noise levels, vibration, and echoes.
Acoustic foam typically comes in squares or sheets, varying in size depending on the room to be soundproofed. A square or sheet will vary in thickness, but all varieties of the foam feature a jagged landscape. This is because even surfaces tend to act as a soundboard for vibration, but jagged edges and uneven surfaces absorb sound waves and deaden them before they can reverberate, causing sound to travel farther and even cause echoes.
Musical purposes are not the only applications for acoustic foam. Industrial settings also often use it to deaden sound not only for the benefit of surrounding businesses and homes, but also for the health of their employees. Live venues and concert halls can host a variety of purposes, and acoustic foam will improve acoustics and deaden echoes for the benefit of the audience. Home theater systems can produce an excess of sound that can leach into other rooms and create strong echoes, thereby deteriorating sound quality. Soundproofing foam can help control vibrations and echoes to improve the sound quality of your home theater system and keep sound from escaping into other rooms.
Large rooms may also benefit from acoustic foam. Churches, synagogues, temples, etc. often have massive spaces to accommodate large numbers of audience members, and therefore sound has a large swath of space through which to travel. In addition, such large spaces often include large expanses of flat wall, which conduct vibration and echoes extremely well. Using jagged foam to baffle the sound can help buffer some of that vibration; in addition, hanging sound baffles--large, flat panels that break up the empty space in high ceilings and large rooms--can prevent sound from traveling far enough to cause echoes by bouncing off more walls.