Does your Room Sound Funny?
Sound is a funny thing. Although it behaves precisely according to well known laws of physics, in practical applications it can be very difficult to predict, much less control. That’s generally because there are too many variables in the equation when it comes to real world acoustics. The walls of the room, the floor covering, the furniture, even the people in the room all affect the way the sound waves behave. By the time music from a loudspeaker reaches the listener’s ear, it has usually been changed by the room to such an extent that there are very noticeable differences, almost always making it worse than it was when it left the speaker.
For home theater rooms, rooms in which people actually listen to music. Or even public spaces where sound quality is important, these room acoustic effects can present a significant problem. Fortunately, there are ways for the average homeowner to substantially remove the room from the audio equation. Acoustic room treatments are used to attack the most common and the most noticeable room acoustic effects.
For home theater systems and music systems capable of delivering deep bass tones, standing waves are often a big problem. Standing waves occur when the sound waves that are created by bass notes are folded or reflected back upon themselves by a room that is smaller than they are in at least one dimension. The sound wave produced by a forty Hertz tone, for example, is fully 50 feet long. This sound wave can be reflected back and forth between the ceiling and floor, front and back walls, or the side walls of the room.
It is helpful to think of sound waves as sine waves with peaks and valleys similar to those of waves on the ocean. When a fifty foot long sound wave is reflected back upon itself, the pressure of the reflected portion is combined with the pressure from the original wave. If the two meeting parts are both above the mid point of the wave, they add up to extra bass. If they are both below the midpoint, then again, the result is extra bass. When one is above the midpoint and the other below, however, they tend to cancel each other out, reducing the amount of bass that can be heard at that particular location.
The net result is that some people in the room hear more bass than was intended in the recording, and some hear less. Almost nobody hears the correct proportion of bass tones in relation to the overall music, unless acoustic room treatments have been applied. The goal of these treatments is to absorb the sound waves before they reflect back into the room from solid surfaces such as the walls. They may consist of single or multiple layers of special acoustic insulation designed to absorb either specific frequencies or broad spectrum sounds. Properly applied, these room treatments can greatly reduce the room effects and let everyone in the room hear the music the way it was intended to be heard.