Acoustics

Acoustics – an overview.

Acoustics is the study of the behavior of sound within space. The echo-less, dry sound of a movie theater is designed for a specific purpose, to relay as accurately as possible the sounds produced by the speakers, free of reverberation. A cathedral with its vaulting ceilings and stone surfaces is rich in reverberation designed to carry voices and complement the music of the organ and choir. Even the air that we breathe has acoustic properties, and fortunately it serves primarily to transfer sound. Each space has different acoustics properties dependent on the shape, size, contents, and composition of the space. When the compression wave of a sound comes into contact with an object three things happen to varying degrees. The sound can be reflected from the surface, absorbed by the surface, or transferred through the surface.

 Sound is reflected from solid, non porous surfaces such as stone, tile, hardwood, etc. In reflection the path of the wave is simply diverted with only a small portion of the energy lost, continuing to carry the wave’s information. This leads to qualities such as reverberation, or how long a sound hangs in the air. You may find that in an area with high reverberation, speech is difficult to decipher. This is because all of the sounds being produced are muddled together into an almost indecipherable wave. This will not however stop the brain from trying.

Sound is absorbed by soft, porous surfaces. When absorbed, the energy from a wave is used to vibrate the object, not passing though or deflecting. In this process, a very small amount of heat is transferred. If we could totally absorb the full sound of all the screaming fans at the super bowl, we would have garnered just about enough energy to heat one cup of coffee from room temperature. When a room is called “sound-proof” it is simply surrounded by sound absorbing materials, sound is unable to transfer though the walls and out the cracks between the doors. There are often special materials (fiberglass being the most common) in sheets on the walls to absorb any stray sound preventing echo and sound transfer.

Transfer is simple, if an object transfers sound well, the object simply carries the compression wave through it. These objects are often not very dense and contain lots of air; they are light and vibrate relatively easily.