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Walled 2D Diffuser - materials and construction advice Books
Old 1st September 2011
  #1
Gear Nut
 

Walled 2D Diffuser - materials and construction advice

So, after many, many days of research, and purchasing of several books, etc... I think I may have settled on creating some standard 2D walled diffusers (the hardest to build of course ). Here's a picture of the type of design idea (not the exact design) I'm going for. The frequency diffusion I'm shooting for is in the 500, 600, or 700 to 5k or 6k range. But this post is mostly about materials and construction, not the math which I'm using QRDude for.

I was very inspired by what G.E. did with his 2D acrylic/balsa wood diffusers, and so I started looking around for somewhere to have the acrylic glass made. That led me to a company called Ponoko, which is perhaps the coolest company I've ever seen. They are able to mill just about anything you can design at what seem to be quite reasonable prices, and so then I started to get carried away thinking: maybe I can make the whole thing out of acrylic glass and just lose the wood all together?

Attached is a sketch of the design idea I came up with. The top half is a side view of a few slots and slats that illustrates how the glass (or other material?) might look from the side once assembled. The bottom shows how it would be constructed, with a tab/ear and slot type configuration.

So here are my questions about this design:

1. How airtight do diffusers need to be? If I were to construct this with the tab/ear and slot design and the use of some type of glue would you imagine it would be air tight enough to do the job? Certainly a very tiny air gap of less than a 1/32 - 1/16th of an inch around the tabs/ears is still more efficient than a standard 2D design without any walls?

2. Is it OK to also use acrylic glass at the bottom of the wells? I've seen people who have put down other diffuser designs that use closed cell foam for diffuser wells claiming that foam was not sufficiently dense and that wood was the only way to go. Is wood truly the only material up to the job of being at the bottom of diffuser wells?

3. Should I put something behind the glass of the diffuser wells? If so what? Absorption? Something else?

4. If not glass then what other material would you recommend? If not acrylic glass I had also thought about making the whole thing out of wood or "hardboard" or even a plastic of some type. My ideal thickness of material is in the .1"-.125" range. Here's a link to a full list of Ponoko's available materials.

5. Should I just abandon the idea of glass at the bottom of the wells and go with balsa or some other type of wood? Does it have to be even denser than balsa?

Whatever wisdom you guys can bestow would be greatly appreciated! Thanks!
Attached Thumbnails
Walled 2D Diffuser - materials and construction advice-2d-walled-diffuser.jpg  
Old 1st September 2011
  #2
Lives for gear
 
boggy's Avatar
Quote:
Originally Posted by oakleaf View Post
So, after many, many days of research, and purchasing of several books, etc... I think I may have settled on creating some standard 2D walled diffusers (the hardest to build of course ). Here's a picture of the type of design idea (not the exact design) I'm going for. The frequency diffusion I'm shooting for is in the 500, 600, or 700 to 5k or 6k range. But this post is mostly about materials and construction, not the math which I'm using QRDude for.
For small rooms i usually go from 1kHz (min. freq.) for diffusion (about 1m minimum distance from diffuser)
Picture show diffusor that can't diffuse frequencies more than 2kHz-2.5kHz, for frequency range up to 5 or 6kHz, your well width must be about 1"
Quote:
Originally Posted by oakleaf View Post
I was very inspired by what G.E. did with his 2D acrylic/balsa wood diffusers, and so I started looking around for somewhere to have the acrylic glass made. That led me to a company called Ponoko, which is perhaps the coolest company I've ever seen. They are able to mill just about anything you can design at what seem to be quite reasonable prices, and so then I started to get carried away thinking: maybe I can make the whole thing out of acrylic glass and just lose the wood all together?
this may be too expensive, but you can try.
Quote:
Originally Posted by oakleaf View Post
Attached is a sketch of the design idea I came up with. The top half is a side view of a few slots and slats that illustrates how the glass (or other material?) might look from the side once assembled. The bottom shows how it would be constructed, with a tab/ear and slot type configuration.

So here are my questions about this design:

1. How airtight do diffusers need to be? If I were to construct this with the tab/ear and slot design and the use of some type of glue would you imagine it would be air tight enough to do the job? Certainly a very tiny air gap of less than a 1/32 - 1/16th of an inch around the tabs/ears is still more efficient than a standard 2D design without any walls?
I always take more care about noise caused by vibration of nearby and not fastened surfaces in diffuser. Some air circulation isn't the worse thing.
Quote:
Originally Posted by oakleaf View Post
2. Is it OK to also use acrylic glass at the bottom of the wells? I've seen people who have put down other diffuser designs that use closed cell foam for diffuser wells claiming that foam was not sufficiently dense and that wood was the only way to go. Is wood truly the only material up to the job of being at the bottom of diffuser wells?
It's not bad if diffuser absorb some sound energy, especially in small rooms (where we never have enough LF absorption)... but if we need diffusion, good reflection characteristic is really necessary
Quote:
Originally Posted by oakleaf View Post
3. Should I put something behind the glass of the diffuser wells? If so what? Absorption? Something else?
Absorption.
Quote:
Originally Posted by oakleaf View Post
4. If not glass then what other material would you recommend? If not acrylic glass I had also thought about making the whole thing out of wood or "hardboard" or even a plastic of some type. My ideal thickness of material is in the .1"-.125" range. Here's a link to a full list of Ponoko's available materials.
i used acrylic glass here: picture

This is a fractal N7M7 diffuser with aluminium fins (1mm) between wells of small diffusers, and with acrylic fins (4mm) between wells of bigger diffuser.
More pictures you can find in this gallery on my facebook page:
Studio Barba | Facebook

Quote:
Originally Posted by oakleaf View Post
5. Should I just abandon the idea of glass at the bottom of the wells and go with balsa or some other type of wood? Does it have to be even denser than balsa?
You don't need to use balsa if you don't need a very light diffuser... use wood which you like, or acrylic glass... it's all good.


Good luck!
Old 1st September 2011
  #3
Gear Nut
 

Thanks for the detailed reply Boggy! I meant for this thread to be more about diffuser materials and construction, but since you brought it up, my understanding is that 1khz = 0.34 meters wavelength. So do you want to be triple the lowest diffused wavelength away from the diffuser? Also, I am planning on building the diffuser with 1.25-1.5" well widths -the picture was just to show what a walled 2D diffuser looked like.

You are absolutely right about the vibration part though... I may end up doing a soft wood for the bottoms of the wells to cut down on the vibration. But what you're saying is that the density of the wood isn't a huge factor?
Old 1st September 2011
  #4
Lives for gear
 
boggy's Avatar
Quote:
Originally Posted by oakleaf View Post
Thanks for the detailed reply Boggy! I meant for this thread to be more about diffuser materials and construction, but since you brought it up, my understanding is that 1khz = 0.34 meters wavelength.So do you want to be triple the lowest diffused wavelength away from the diffuser?
No, I'm not only one that want this. Audible problems with phases near to diffusers are well known phenomenon.
Quote:
Originally Posted by oakleaf View Post
Also, I am planning on building the diffuser with 1.25-1.5" well widths -the picture was just to show what a walled 2D diffuser looked like.
Ok.
Quote:
Originally Posted by oakleaf View Post
You are absolutely right about the vibration part though... I may end up doing a soft wood for the bottoms of the wells to cut down on the vibration. But what you're saying is that the density of the wood isn't a huge factor?
Density and stiffness of wood is a factor which have influence on intensity and character of reflections.... but, any wood is primarily reflective.
Old 1st September 2011
  #5
Gear Nut
 

Quote:
No, I'm not only one that want this. Audible problems with phases near to diffusers are well known phenomenon.
I didn't mean you personally But am I correct that the rule is that listening position should be 3x distance of longest diffused wavelength?

I think I'm going to start designing this thing in earnest later on this week. More pictures to come. Will take any feedback anyone can offer!
Old 1st September 2011
  #6
Lives for gear
 
boggy's Avatar
Quote:
Originally Posted by oakleaf View Post
I didn't mean you personally

Quote:
Originally Posted by oakleaf View Post
But am I correct that the rule is that listening position should be 3x distance of longest diffused wavelength?
yes, 3x or 4x if you want to be sure.
Quote:
Originally Posted by oakleaf View Post
I think I'm going to start designing this thing in earnest later on this week. More pictures to come....
Great!!!
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