All QRDs have high- and low-frequency limitations. Skylines, Other Odd Names: some of the real QRD products, like “skylines” and fractal-based stuff, are actually decent diffusors (math done well) – but they only work above 2-3KHz, and a high-quality, high-value acoustic diffusor works down to a mid-low frequency – good diffusors are as broadband as possible. Plain and simple – these are not diffusors. They’re simply high-frequency (and only at a single frequency, usually about 4KHz) resonator/redirectors. Open slat-grids: I see these advertised as “diffusors”, and I do not know why someone thinks these diffuse anything. And don’t get me started on vacu-form anything! Redirectors (any treatment products with hard flat surfaces, such as pyramids, polygons, wedges, and the like): these offer only another set of flat-surface reflection angles but do not evenly diffuse sound, and they’re highly frequency-dependent (they only redirect above their dimension/wavelength, typically above 3-4KHz). Personally, I don’t like phase-shift-based diffusors (which is how QRDs work – they smear the phase/timing reflection content), but I especially dislike fake ones, which are money wasted (that includes the dude who apparently gathers scrap-wood pieces from somebody’s carpentry shop floor, glues them randomly together, and calls them “diffusers” – as I said, junk, though it makes a funny joke present to an acoustics guy). Many companies have obviously not done the math. They are the result of someone in a company saying to their staff “we need something we can call a diffusor” (or “diffuser”, there’s a bit of confusion there as well).įake Quadratic-Residue Diffusors (because of thick barrier walls, missing cavity walls, random non-math-devolved depths or “skyline” heights, etc.): QRD-type products require a deep knowledge of the science involved, with well-thought-out math computations. They are not the result of scientific consideration, effectiveness, evenness, value, or quality. OK, plain and simple: there are a lot of “diffusion” products which are junk. This may have an effect on my blog.įrom Wikipedia: “ Diffusion, in acoustics and architectural engineering, is the efficacy by which sound energy is spread evenly in a given environment… Virtually all spaces are non-diffuse… Small sound spaces generally have very poor diffusion characteristics at low frequencies due to room modes.” Full disclosure: Acoustic Geometry makes the World’s Best Acoustic Diffusors.
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