Control of the focusing power of concave surfaces can be achieved by constructing convex angles and diffusers on opposing surfaces . For example , the focus across the room , caused by a concave angle , will be diffused , redirected , or confused by a convex angle at its point of focus .
CONVEX ANGLES Convex angles diffuse reflections . A convex angle comes to a point or bends toward you , leaving only one point where the sound wave can bounce directly back in the direction from which it came . All other points on the convex angle deflect the sound wave . In construction , convex angles offer an excellent means to transform axial modes into tangential or oblique modes .
Convex angles help redirect potential axial standing waves into much less destructive tangential waves . The proper implementation of convex angles can help transform an otherwise unusable acoustical environment into a reliable creative studio .
TREATING SURFACES Most acoustic designs incorporate a blend of hard and soft surfaces , controlling reflections rather than eliminating them . This provides a comfortable and creative environment . A recording studio that has been overly deadened using lots of absorptive surfaces , lacks life — it is an unnatural listening environment and feels uncomfortable to most listeners .
ABSORPTION COEFFICIENT ( ABSORBERS ) As we implement absorptive material , we must be aware that each material has a unique ability to absorb specific frequency bands with varying efficiency . The quantification of this absorptive trait is called the absorption coefficient . This reaction to sound waves is rated at a specified frequency and noted in terms of absorption effectiveness .
Diffusion panels randomize reflections . Their physical design , in a seemingly random pattern , effectively disperses otherwise focused waveforms .
An open window into outer space is the typical image representing 100-percent absorption because all sound enters and none returns . We think in terms of percentage and speak in terms of two decimals . A material that absorbs half the energy at the specified frequency is said to have an absorption coefficient of . 50 . An open window is said to have an absorption coefficient of 1.00 .
All materials exhibit an absorption coefficient : wood , fabric , glass , marble , and so on . As we consider , for example , our list of standing waves , if we notice coincident modes at 240 Hz , isolated by 35 Hz from adjacent modes , it might do us a lot of good to include materials in the design that exhibit a high absorption coefficient at about 240 Hz . In this way , we can use the existing space effectively , controlling the problematic tendencies rather than simply dealing with the problems . This simple example is the basis for much of what designers consider when they select dimensions and materials .
The absorption coefficient is specified at six frequencies : 125 Hz , 250 Hz , 500 Hz , 1 kHz , 2 kHz , and 4 kHz . Remember , the closer the