1d or 2d QRD diffusor

[4 the Max]

First, I am so honored and thankful that Mr. Winer replied to my posting in the So little time, so much gear forum; I posted there because nobody replied in this forum.

I am grateful for his generosity in providing Bass trap plans on his acoustic forum, his YouTube, and RealTraps videos comparing sonotube, bookcases, his Realtraps diffusor, etc. (I've also really enjoyed his musical videos of himself playing various instruments)

I have been doing a lot of research on internet about diffusors and learned that the PME Records QRD diffusor is actually a 2-D Shroeder-based QRD diffusor

PME Records QRD Diffusor Construction

while this is a 1-D Shroeder-based QRD diffusor that uses wells.
QRD Diffuser Well Depth Calculator

Questions:
1. When do you use a 1-D or 2-D QRD diffusor? For example, which one would go on a ceiling, which one on a wall?

2. How do you know what minimum and maximum well depth to enter?
How do you know what well width to enter?

These questions go with this concept: How do you know which frequency that you want to diffuse, because from reading similar posts, the well width is 1/2 the frequency of the one that you want to diffuse (I think I got that right.)

Thanks again. I hope that other forum members can also benefit.

Some great references on the topic:

F. Alton Everest Books: Master Handbook of Acoustics, Studio construction on a budget

http://www.soundscapes.nu/d_plan.htm
http://www.soundscapes.nu/!gallery/design/index.htm

http://www.subwoofer-builder.com/qrdude.htm

http://www.rpginc.com/news/library/tyndall_paper.pdf

Acoustic Diffusers

Calculate a Two-Dimensional Primitive Root Diffuser (Skyline)

FAR acoustic panels

Glossary: Schroeder Diffusers | Sweetwater.com

Diffusion (acoustics) - Wikipedia, the free encyclopedia

hunecke.de | Quadratic residue diffusors (QRD)

Videos:

Bass traps:
YouTube - Broadcast Yourself.

Diffusers:
(spanish)

YouTube - 1D QRD Acoustic Diffusor

YouTube - Difusor acústico QRD 1D

YouTube - Construccion difusor QRD experimental

YouTube - Construccion difusor QRD experimental

English:
YouTube - Jocavi® at the 122nd AES Viena 2007
YouTube - 06-08-08 (III) Sound diffusers

------------------
Ethan Winer:

Diffuser:
YouTube - ProRec 127th AES Coverage: RealTraps Diffusors
YouTube - All About Diffusion
All About Diffusion en Yahoo! Video
All About Diffusion on Vimeo

Listening room and acoustic treatment:
YouTube - How to Set Up and Treat a Listening Room
YouTube - The Ultimate Home Studio
YouTube - Recorded Realism

Minitraps:
YouTube - SoS Minitraps acoustic treatment tutorial

Audio myths:
YouTube - Audio Myths Workshop

Music:
YouTube - Amazing Video of a Song Composed Entirely of 37 Cello Parts
Tele-Vision - Video
YouTube - Tele-Vision


Factory:
Made in Connecticut - RealTraps factory tour on Vimeo

Modal resonance and ringing:
YouTube - Modal Ringing and Resonance

[gremmy]

A lot depends upon:

1) In how many directions is it useful to scatter the energy? (1D diffusers scatter sound left/right, while 2D scatter left/right/up/down) -- Assuming a few things about orientation, of course.

2) How much do you want to lower the level of the diffused energy before it returns to the listening position? (assuming a single listening position, 2D diffusers will produce lower level reflections because more of the sound energy is being diverted away from the listener). - again, I am assuming some things about orientation. And don't forget about BAD panels -- these tend to absorb about 50% of the energy in the frequency range where they diffuse.

3) How close to you need to sit to the diffuser? From most distance required to least, the diffuser types are as follows: Poly, 1D QRD, Skyline, 1D BAD, 2D BAD.

[4 the Max]

Thank you for your very quick reply.
Question:

How do you know what minimum and maximum well depth to enter?
How do you know what well width to enter?

These questions go with this concept: How do you know which frequency that you want to diffuse, because from reading similar posts, the well width is 1/2 the frequency of the one that you want to diffuse (I think I got that right.)
===================

I am building a drum, acoustic instrument, and amp isolation recording room. It is not a listening room.

threads are here, because I didn't get a post in this studio construction sub-forum.

Acoustic treatment - drum room

Acoustic treatment - drum room
room width = avg. 24' from wall side 1 to wall side 2 (splayed, so the walls are not parallel)

1. wall side 1: 17' L x 10' H (covered by 12" cedar wall Tongue and Groove planks)

2. wall side 2: 12' L x 16' H (helmholtz bass traps) + 5' for entrance door

3. End wall 1: sliding patio door covered by curtain; End wall 2: steel plated entrance door (covered by sheet of Auralex 2" pyramids) [entranceway into bathroom and storageroom]

4. The ceiling slopes from 16'H to 10'H and is covered with pine tongue and groove

5. Ethan Winer DIY bass traps in the vertical corners and between the walls and the ceiling

6. hardwood floor with area rug underneath bass drum so it doesn't slide

[gremmy]

I'm not going to pretend to be an expert on studio design (I'm sure others will chime in here with better advice than I could provide). I think a lot depends upon what your goals for the room are.

Personally, I use acoustic treatments for my home-theater/listening room, where I have implemented an RFZ (reflection free zone) in the front half of the room and a highly diffuse zone in the rear of the room. In my application, I want as flat a frequency response as I can get, which means bass traps in the corners to address modal issues. To achieve my RFZ, I have absorbers at early reflection points. And beyond the RFZ, my goal is to diffuse everything, within reason. Since I can't reasonably diffuse anything below 500hz or so, I generally aim for a lower limit frequency somewhere in that range. I would like to diffuse frequencies all the way to the upper limit of human hearing, but I don't have the skills to build fractals (at least not yet), so my diffusers cut off somewhere between 6880hz and 9500hz.

As far as well width and depth go:

Depth controls how low it will diffuse (the deeper the wells, the deeper the diffusion) and width controls how high (narrow wells diffuse higher). If you go too narrow for a given depth, you'll start losing sound energy to viscous losses. If you go too deep, you may need more room than you have between the diffuser and the seating position.

QRDUDE has excellent tutorial info that explains most of this stuff.

[boggy]

Originally Posted by gremmy

..... And beyond the RFZ, my goal is to diffuse everything, within reason.

I like it....

Originally Posted by gremmy

Since I can't reasonably diffuse anything below 500hz or so, I generally aim for a lower limit frequency somewhere in that range. I would like to diffuse frequencies all the way to the upper limit of human hearing, but I don't have the skills to build fractals (at least not yet), so my diffusers cut off somewhere between 6880hz and 9500hz.
.......

Frequencies beyond 10kHz aren't easy for diffusion, because you (first) must hunt tweeter sweet spot (only way to get that high frequencies), and if you build diffusors from materials that aren't very reflective (like ceramics, or similar hard surface), your precious high frequencies will be still mainly absorbed than reflected.

regards

Boggy

[PaulP]

Those Blackbird diffusors look more like absorption to me.

Paul P

[lolcatz]

What frequencies will the PME 2D diffuser be effective at?

[localhost127]

Originally Posted by lolcatz

What frequencies will the PME 2D diffuser be effective at?

the "PME QRD" is actually based on primitive root number theory, not quadratic residue as is continually propagated - thus, it is a 2D PRD reflection phase grating diffuser.

and it does not adhere to the number theory for a PRD based on well counts. upon closer inspection, the diffuser is actually an array of many smaller PRDs - as designed by BBC and you can investigate and explore in the following document:

http://www.bbc.co.uk/rd/pubs/reports/1990-15.pdf

if you are looking to build a QRD or PRD, it would be best to utilize an online calculator and design based on your own personal criteria - vs that of another application which may not be applicable to you.

2D PRD calculator;
Calculate a Two-Dimensional Primitive Root Diffuser

1D/2D QRD calculator;
QRDude: Quadratic Residue Diffuser calculator

and it would be wise to spend some time reading through QRDude's technical guide - written extraordinarily such that the information is easily digestible for the novice..

what is the application for the diffuser you are looking to construct?

[lolcatz]

I'm moving into a new live room soon with the dimensions of 40x20 with 13 foot ceilings. I'm already set with adequate bass traps, as for now I'm looking for an efficient broadband diffusion method to diffuse frequencies instead of using too much absorption. With these dimensions what do you think would be the appropriate action?

[localhost127]

Originally Posted by lolcatz

I'm moving into a new live room soon with the dimensions of 40x20 with 13 foot ceilings. I'm already set with adequate bass traps, as for now I'm looking for an efficient broadband diffusion method to diffuse frequencies instead of using too much absorption. With these dimensions what do you think would be the appropriate action?

being in that large of a room is a good start - but getting good surface area coverage with reflection phase grating diffusers can quickly become expensive and time-consuming...

you could get away with building a diffractal - which basically means a nested array of diffusers, which can greatly increase the bandwidth to a lower effective frequency, granted that you are sufficiently in the far-field of the diffuser (~3x design frequency spaced from diffuser).

1D N23 QRDs
1" well width
~10" max well depth
600hz design frequency
6880 HF cut-off frequency

^build 11 of those, and arrange the 11 N23 diffusers into a larger N11 array.

1D N11 QRD
23" well width (each N23 diffuser)
~52" max well depth
200hz design frequency



*note, N23s should be Normal and Inverse, adhering to Barker Code (not shown)

total array size = ~ 21ft.
minimum distance to diffuser = ~16ft+

[lolcatz]

thank you for taking the time to give me an excellent response, so does the PME 'diffuser' serve more as eye candy than actual functionality?

[localhost127]

Originally Posted by lolcatz

thank you for taking the time to give me an excellent response, so does the PME 'diffuser' serve more as eye candy than actual functionality?

the BBC PRD is still functional, but it has limited bandwidth due to it being an array of smaller PRDs.

if you wanted to design a 2D PRD/QRD, it would be best to utilize one of the above calculators based on your own physical size criteria and bandwidth.

the ceiling of the Blackbird C room shown above in this thread is an example of a 2D diffractal PRD,