# Thread: Building a 2D QRD Diffractal Diffusser

1. ## Building a 2D QRD Diffractal Diffusser

Hi Everybody,
I am building a new 5.1 surround film and video studio. Because of the distance of the seating position from the back wall (3m or 10feet) I decided to skip the 1D QRD design and to go to 2D QRD diffractal design that will help me to further diffuse the sound, spread the diffusion bandwidth and deal with lobing effects problem. I was thinking of building a 2D Prime Number 7 Diffractal Diffuser in the back of the room. I am using Rod Gervais Quadratic_Diffusor.xls spread sheet (found here: http://www.rodssoundsolutions.com/Outside.html with other useful things) to calculate the design and high and low frequencies as well as depth and width of the well openings. I learned the basics of QRD reading the “Master handbook of acoustics”-F. Alton Everest. Unfortunately in the book only 1D QRD are explained in detail and the 2D are just described. From what I can see from Rod Gervais design, the 2D matrix is formed from phase shifting of the Prime number 1D QRD sequence. I bought Rod Gervais “Home Recording Studio: Build It Like The Pros” book expecting it by Sunday hope to learn some new interesting things.
Looking at the RPG Omniffusor and Hemiffusor they are using different way of phase shifting of the 1D Prime Number 7 QRD diffuser to form 2D matrix.
I have few questions:
1. In the Rod Gervais Quadratic_Diffusor.xls spreadsheet I found something confusing. Knowing that in 1D QRD design high cut frequency of the diffuser is given by width of the well opening, when I change the value of the width of well opening in this spreadsheet only design frequency is changing. Actually I get changes of high cut frequency only by changing the depths of the well and the prime numbers. So what is this design frequency?
2. Will this Diffractal design work with 2D diffuser?
3. As it is not practice to use diffuser in film mixing studios should I skip this idea or just go for it?
4. If you know any link that would describe the way the 2D QRD works with the calculation equations please let me know.

Thank You all very much for Your time and all of your suggestions are welcomed.
Best regards,

Joka :D

P.S. Can anybody that speaks Finnish translate this skyline calculator .xls spreadsheet : http://kotiweb.kotiportti.fi/audiovi...kylinekuva.xls.
Or if you know some online Finish to English translator even better.
And does the http://www.mhsoft.nl Acoustic calculator work properly?
I was considering building some Skyline PRD for the side walls and ceiling.

2. ## Re: Building a 2D QRD Diffractal Diffusser

Originally Posted by Joka
Knowing that in 1D QRD design high cut frequency of the diffuser is given by width of the well opening, when I change the value of the width of well opening in this spreadsheet only design frequency is changing. Actually I get changes of high cut frequency only by changing the depths of the well and the prime numbers. So what is this design frequency?
The design frequency is the frequency of maximum diffusion. Above and below this frequency efficiency falls off.

Will this Diffractal design work with 2D diffuser?
I honestly do not know the answer to that question.

As it is not practice to use diffuser in film mixing studios should I skip this idea or just go for it?
I doesn't seem to be that this wold be desirable in a surround sound environment - but I also have to admit to very little experience in that environment.

If you know any link that would describe the way the 2D QRD works with the calculation equations please let me know.
This is a pretty good paper from Trevor Cox:

http://www.acoustics.salford.ac.uk/s...ser_design.pdf

I hope that helped a little,

Rod

I read the Mr. Trevor Cox Diffuser_design.pdf and found it very interesting.
I will continue to research about diffusers and if something interesting comes up I will post it back to this thread.

Best regards,

Joka :D

4. I have found very interesting link:
http://www.diffusor.com/English/Index2.htm
This company already has practical implement of 2D QRD diffractals combining with Helmholtz low frequency absorbers.
They even have 2D PRD Skyline type diffuser difractal combined with 2D QRD diffuser.
Looks very interesting.

Have fun.

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