Anechoic chambers allow you to conduct tests for various problems. They absorb environmental sounds so that you hear only the specific sounds directed at you. These chambers don't work that much differently from a sound booth, but their promise of absolute quiet save for the directed sounds you produce requires special materials.
Open-Cell Foam and Absorbing Sound
There are no hard materials in an anechoic chamber because anything hard will reflect sound. When you're in a situation where you need to record or hear very specific sounds and nothing else, you don't want even a whisper of an echo. The material you find in the room is soft, from carpeting to foam all over the walls. This foam can be of a number of materials such as melamine and polyurethane, but the key is that it has to be open-cell. This is what it sounds like, a foam where the cells that make up the foam are wider and have more space, which traps sound waves and makes them disintegrate. The result is that sound is absorbed and not merely halted, which carries with it the risk of some sound reflection. Absorption takes in the sound and doesn't send it back out into the room.
All Those Spikes
Rather than just padding all the surfaces in the room with foam, those setting up anechoic chambers use foam that has ridges, soft spikes, waves, and more. These formations help rip up sound waves as they encounter the foam surfaces. Depending on the configuration of some of the ridges, they could also cancel out sound waves as the waves advance toward the walls, floor, and ceiling.
Rather than trying to figure out how to best cover everything to create an anechoic chamber for your needs, you might consider getting a compact chamber system that provides you with all the materials you need.
All this foam needs to be attached to the walls, ceiling, and floor somehow. Most solid connectors, such as staples or nails, will transmit vibration and can potentially reflect some sound waves, ruining the anechoic effect. Glues and caulks can crack, opening up ways for sound to escape. It might not seem like that big a deal to someone not working on a project that needs total ambient sound absorption, but to those involved, it's a huge leak that needs to be eliminated. In an anechoic chamber, materials are connected with acoustic caulk or adhesive, which is designed to remain somewhat rubbery and flexible. This eliminates cracks and pulling, which can separate parts of the caulk from a surface.
If you're buying a compact anechoic chamber system, ensure the materials used are totally geared toward sound absorption. You should find the parts fit together without any gaps. If something in the design does not seem intuitive to you, contact the manufacturer rather than trying to modify it yourself.
For more information on a compact anechoic chamber, contact a company like MilliBox.