Despite what the salesman at your local A/V shop tells you, sound proofing and sound treatment are not interchangeable terms in acoustics. Sound proofing is the process of creating a space that prevents any form of sound from escaping it, while sound treatment is the manipulation of a room's response to particular frequencies to create a balanced sound within the room. Although there are similar materials for both procedures, their expected outcomes and processes are nonetheless very different.

Sound proofing a room

If you're creating a space that will be used to contain a huge amount of sound and noise (like a death metal band's rehearsal space), the best way to do this would be to build a room within a room. The room itself should have a thick cement floor, walls and ceiling. This forms an outer shell which is the space's last line of sound proofing, and must be dense enough to absorb even the loudest low frequency sounds.

Within it, another room must be made whose walls, ceiling and floor (ideally) may be made of cement as well to ensure maximum density. Drywalls filled with sheetrock or fiberglass can also be used. This inner room must be smaller than the outer room and is generally placed in the middle of it, allowing for a space between them where the resultant escaping sound is trapped even more. This ensures that only a minimum of sound meets the walls of the outer room, thus increasing the chances of a 100% sound proofed room.

Treating a room

Treating a room requires less material than sound proofing it, but requires more patience and knowledge as there will be frequent listening tests and adjustments to be made in order to create a tailor-fit sound. There are three ways to treat a room, either by sound absorption, reflection or diffusion.

Sound absorption is important in an acoustically treated room/studio because it eliminates standing waves and early reflections from surfaces. Taming these undesirable sounds also creates a clearer and more precise stereo image, as in the case of a mix engineer's suite. Sound absorption is achieved through the placement of porous material such as cloth and fiberglass in strategic areas. These act as traps that absorb high and mid frequencies, and are generally placed around the room and on the ceiling. To trap low frequencies, denser absorbers (called bass traps) are placed in locations that form corners, such as between walls and in spaces where the room's wall's meet the ceiling.

Diffusion serves to scatter sound hitting its surface in random directions. Though less ubiquitous than absorbers and reflectors, diffusers serve an important purpose of preventing redundant travel of sound waves. Diffusers are generally crafted with a mathematical model as a guide to ensure the randomness of its surface. Once sound arrives on the face of the diffuser, it is distributed in an arbitrary manner.

The next time you decide to create a quality listening space, define first whether or not you would like to sound proof it, treat it, or even both. Knowing what you would want to do ahead will save you energy and money by letting you focus on what would be the priorities for your acoustic project.