diffusor plans?

[Professor]

I kinda like the design of this room when I first saw the photos:


Of course, I've never been in it or heard the sound, but the concept seems pretty obvious as a completely random diffusor design. I imagine that interspersing or surrounding the stone with absorbant materials like rigid fiberglass would be helpful as well, and it looks like the purple wall to the left side is cloth-covered fiberglass (not sure how thick). It's probably not real river rock either, but more likely is a flat-backed "cultured stone" that can be mounted like wall tiles - casually referred to as 'lick-n-stick rock'.

-Jeremy

[Mark Alan Miller]

in my copy of "recording studio design" by philip newell, he recommends a pattern of wood strips and voids (which would, I presume, be fabric covered fiberglass, although the depth and density of the fiberglass is not specified. There IS, however, a mathematical pattern specified. it is "5(wood), 3(void), 4(wood), 4(void), 3(wood), 5(void), 4(wood), 5(void), 3(wood)", at which point the numerical pattern repeats, with the void first (5v,3w,4v,4w,3v,5w,4v,5w,3v), etc. He calls it an "amplitude reflexion grating" It doesn't look like the exact same pattern wes uses, but, hell, it's in a book, so it MUST be true.... (figure 4.33, page 100, "recording studio design" by phillip newell.
brian

Excellent! Thanks for that!
I suspect, as is in other "flat diffusor" designs, that the voids are also wood. It's how the differing reflections and the refraction off of the edges combine that makes it diffuse sound, and if you added absorption in the voids, that would likely remove some critical reflections... (but might sound good in a different way?! anyone?!)

[brian beattie]

I think this type of diffusor requires reflective and absorptive surfaces alternating. The philip newell book says that ANY juxtaposition of reflective and absorptive surfaces will cause diffusion because of the phase change at the boundary. I suspect it WORKS partially by "removing some critical reflections"...
brian

[Mark Alan Miller]

I could stand corrected. On closer inspection it looks like that's what's going on in Wes' designs. I don't recall or have any notes on this from TapeOpCon 2004, so there ya go. Anyone else weighing in on the absorptive vs reflective backing to these "flat" designs?
Keep the info coming! It's excellent.

[goldstar]

The original math done on these by Mannfred Schroeder does not include any absorption, though RPG (and others) have incorporated absorption, too. Chapters 13 and 14 in Everest's Master Handbook of Acoustics have the details, and more math than I can handle after a long day of work.

Frank