Three Sound Things
Three things happen to sound energy in our rooms. Sound energy is either absorbed, reflected, or diffused. Sound energy that is absorbed is physically changed to heat through the process of absorption. When it is changed to heat it is no longer sound energy but heat energy. When sound energy makes this physical change it can never be sound energy again. The sound is lost forever. Sound energy that is reflected is sound energy that strikes a said surface and then is “thrown” in another direction, usually with not much loss in strength. The direction the reflected energy is “thrown” is dependent on the shape of the reflector. Diffused sound energy is sound energy that is “broken up” into smaller parts and spread out in some type of sonic array depending on the device used to generate the diffused energy. In our rooms and it doesn’t matter what type of room it is the processes of absorption, reflection, and diffusion that occur and must be acoustically dealt with.
Sound absorption in our rooms can be broken down into two general classes. We have middle and high frequency absorption which deals with our speech and musical presentations. We also have another class which is low frequency absorption or the term used is bass absorption. We need to use sound absorption in our rooms to reduce excess and usually unwanted sound energy. When we absorb excess energy of any class in our rooms, we can hear more of the sound produced by a person or instrument and we can also hear that same sound more clearly. For middle and high frequency absorption, we can use carpeting on the floor, draperies over our walls and windows. For low frequency absorption, we can use pillows and even thick padded chairs. We must place these chairs and pillows in the proper room locations to maximize their sound absorbing properties. Low frequency energy resonance try to “hide” in different room locations, especially the corners.
Sound reflections within our rooms must be controlled because they confuse our brains with too many mixed signals. Our brains need to localize or focus sound that comes from one direction at a time. We are not very good at separating numerous sound sources all coming at us at once from different directions. This is exactly what occurs with wall and ceiling reflections at our ears. We hear all these sound “sources” bouncing off every wall, ceiling, and floor surfaces into our ears and our brains can’t process all that data at once. Our brain needs simple and clear sounds, so we can hear someone speak to us. We can hear all the tonal inflections and timbre that a person’s speech creates. We need to hear for emotional content and meaning. Sound reflections from our room can be controlled in the same manner as we used before using the process of absorption. We can use drapes and window coverings. Furniture not needed much here because with reflections we are dealing with middle and upper frequency control, not low frequency sound absorption.
Sound diffusion occurs when sound energy is “broken up” into smaller units and then spread out in a certain type of array or pattern depending on the diffusor type used. We are most familiar with light diffusors. The plastic cover on a florescent light fixture has little bumps in its surface. These “bumps” represent a type of light diffusor which takes the light from the florescent bulb and spreads it out over a larger space in the room. Light diffusion and sound diffusion are similar In our rooms, sound energy strikes a surface and if that surface is flat that energy will be reflected. If the surface in our room is not flat but rather has high and low places sound diffusion can occur, When sound energy in our rooms strikes a piece of art, sound energy is re radiated out in different directions in our room depending on the art foam configuration. It is almost like we are creating numerous smaller reflections from the original sound pressure energy. This spreading out of sound energy in different directions is usually reduced in strength which allows our brains to localize and hear more clearly the original signal.
In our rooms, no matter what the usage, we have sound reflection, absorption and diffusion occurring. We use a the later two to control the first. We use absorption and diffusion to control sound reflections all to hear better.