Question on QRD diffusers

[javajaws]

Thinking about building a QRD diffuser. I've seen references to fin width (keep as thin as possible), but I haven't seen much on the specifications on the bottoms of the wells (assuming the build style leaves the cavities behind the wells open to the back/backerboard). How thin can they be? Can't they (and/or the fins themselves) be too thin so as to resonate or otherwise be ineffective? Is resonance really the only thing to worry about? Or do they just need to be airtight?

Also, all the calculators seem to specify the width of the wells as it relates to depth - but I don't see much about the height (top to bottom when hung on wall) of the diffusor. How does height affect its effectiveness? Is it just a case of higher (larger) = more effective?

 

[headshake]

https://www.nature.com/articles/s41598-017-05710-5

https://journals.aps.org/prx/abstract/10.1103/PhysRevX.7.021034

The depth is 1/2 the length of the wavelength for a QRD. The second link has a design that is 1/20th the wavelength.

ripped from the web:
QRDude: Quadratic Residue Diffuser calculator
Calculate a Two-Dimensional Primitive Root Diffuser

What calculator are you using?

I've thought about making a diffuser. Good luck! I wish I could answer more. I am sure someone will chime in.

wavelength calc:
http://www.procato.com/calculator-wavelength-frequency/

 

[javajaws]

Using QRDude...

 

[Yuri_B]

Trevor J. Cox and Peter D'Antonio "Acoustic Absorbers and Diffusers: Theory, Design and Application". A quote from this book: "The fins should be as narrow as possible, but not so narrow that they vibrate and cause significant resonant losses".

The QRDude application takes into account the fin width. So the fin width need to be made thicker? When the fin width = 16mm, the true diffusion frequencies are: 500 1000 1500 2000 2500 3000 3500 4000 4500.

So Manfred R. Schroeder was wrong about his diffuser or the QRDude application is wrong.

 

[olieb]

Thinking about building a QRD diffuser.

I would rather build a (poly)cylindric diffuser. Much simpler and maybe even more effective.
Here is an article for information.

R&D Stories: Acoustic Diffusion Research

This article offers a valuable inside perspective about developing new diffuser solutions, and lessons learned while designing countless critical listening rooms around the world. A journey that lead to the creation of the PolyFlex diffuser, which will scatter either horizontally or vertically...

audioxpress.com