Home Audio, Sound & Acoustics

Say – what is all this ‘cue-sticks’ stuff, anyways? Well, acoustic treatments help control the sound in the room. You might visualize sound from a loudspeaker or subwoofer kind-of like dropping a quarter into a bathtub full of water. It drops in, making waves on the surface that move outward and then bounce of the sides of the tub, reflecting around for quite awhile. If the waves were sound, that first wave from the quarter directly hitting your ear will make a nice, clear, intelligible sound.

The problem comes in when the rest of the waves bouncing around continue to strike your ear, from multiple directions, delayed by varying amounts of time. Although our brain is astoundingly good at figuring out which signal arrived first and understanding the basic content of the sound, it gets a little confused about which direction it came from, and the true tonal quality and subtleties.

The fact is, the vast majority of what we consider to be audio fidelity is completely morphed and man-handled by the air between you and the speaker, along with all the reflections that merrily bounce off the walls, floor,  and ceiling. When you think about it, it’s amazing we can understand anything at all. To figure it out, humans use a three-piece pattern recognition system consisting of the left ear, right ear, and a grey ball of mush called our ‘brain’. Try this sometime in a noisy, crowded, indoor space: tightly close off one of your ears with a finger. All of a sudden, the environment sounds much more random, and the brain has a hard time distinguishing sounds and figuring out where they came from. T

here are two primary ways of controlling all this chaos in a theater room. The first method has to do with controlling the dispersion of the speaker itself. If you don’t want reflections from the ceiling, then don’t send sound in that direction in the first place, silly. This might be accomplished with types of horns, baffles, or tall and skinny line array speakers. The second method handles the sound where it strikes the wall or boundary.

Absorption is one method of dealing with the waves as they approach theater room surfaces. Most absorption materials, such as fiberglass or cotton panels, are porous to a varying degree so that sound pressure waves must push their way through, bounce off the wall, and then push their way back out. All this resistance knocks the energy out of the wave, maybe even stopping it. Imagine riding a bicycle down a sidewalk near the beach. You can move along quite easily unless you veer off into the sand, where you slow down quite quickly or even stop due to the friction of pushing through the softer material.

Diffusion is another method of keeping sinister reflections from gittin’ ya. But I’ll defer the de-confusing diffusion discussion until another not-too-distant discourse.
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Sean Hotchkiss
shotchkiss@localhost