diffusor design

outerwave · Post by **outerwave** » Wed Mar 09, 2005 2:09 pm

i asked this before but i realize i posted the wrong forum...

my main recording room is an irregular 20'x30', where the ceiling is parallel to the floor for 80% of the room. i was looking for a cost effective diffusor solution for the ceiling; let me know what you think...

using 2'x4' sheets of plywood or fiberboard, 1/8" to 1/4" thick, i would pull two of the edges together (the 2' sides) to create a "U" with a depth of about 12". brace these and mount 10 or so to the ceiling to break up the flat surface.

should i sutff the space behind these with any material? cover the face with anything? (i might sprayglue some cloth of for cosmetics) is 1/8" plywood thick enough to diffuse a decent amount of energy. again this is a cost effective solution.

i do not know what this design is called, so i do not know what to look up for info or stats. also, does this compare well to other designs?

thanks (again)

knightfly · Post by **knightfly** » Thu Mar 10, 2005 8:38 pm

Nathan, first off, welcome to the board; If you can, please edit your Profile to include a location; next, there's a whole procedure that, if you follow it, helps us save some time (so we can help others too) - it's at the top of the Construction forum.

Your specific question - these are called Polycylindrical Absorbers - if you add insulation inside that does NOT touch the curved panel, they act as a panel trap for absorption, as well as acting as a "1D" diffusior; so if you want less specular reflections, you can put some of them in one axis and some in the second axis.

If you don't want any bass trapping, then the insulation inside can/should touch the front panel. However, most applications can use the extra trapping/absorption.

There is a small section on these in Alton Everest's Master Handbook of Acoustics, it's about $25 from Amazon or you may be able to find it in your library. The section on Poly's starts on page 212.

HTH... Steve

Ted Nightshade · Post by **Ted Nightshade** » Fri Mar 11, 2005 12:56 am

One thing I remember from the Everest book is that you want random "chord" lengths (that would be your 12" in your example, I do believe) for your "polys". Not all the same chord length. So maybe some should be 12", some 6", some 17", not all the same.

outerwave · Post by **outerwave** » Fri Mar 11, 2005 6:53 am

Ted Nightshade wrote:Not all the same chord length. So maybe some should be 12", some 6", some 17", not all the same.

so is that the depth, thus changing the degree of curve on the different units? a commercially available one is all the same length and depth.

also, i will be sealing them and filling with foam to create a basstrap.

knightfly · Post by **knightfly** » Fri Mar 11, 2005 1:00 pm

http://www.electroacoustics.co.uk/artic ... uzpoly.htm

May give some help; Everest's Master Handbook of Acoustics ($25 at Amazon.com) has the description Ted referred to, but I tend not to post others' copyrighted works - the explanation with some pix is on page 209-213; if you can't afford or don't have the book, maybe your public library will.

Don't use foam inside a trap; fiberglass works better even than acoustic rated foams.

One way or another, I'd recommend reading the Everest material before starting this.

One reason commercial poly's are all the same size is ease of fabrication on an assembly line, BTW... Steve

outerwave · Post by **outerwave** » Fri Mar 11, 2005 3:04 pm

knightfly wrote:http://www.electroacoustics.co.uk/artic ... uzpoly.htm

May give some help; Everest's Master Handbook of Acoustics

I ordered Everest's book a few days ago, just waiting for it to arrive...

cadesignr · Post by **cadesignr** » Sun Mar 13, 2005 4:14 pm

I hope you bought flashlights, rope, and anything else you need to climb back out of the rabbit hole.

Took me 10 years to find a way out. Say hi to the queen of hearts while your down there.

Oh, BTW. The section on quadratics doesn't mention they are 1/4 wavelength silencers too.
fitZ