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DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)
Old 3rd April 2017
  #751
Here for the gear
 
Hi Tim,

I'm trying to improve the acoustics of our living room.
On a mantelpiece, I want to add a A1-LF diffuser (just two elements, total width 84 cm), made of MDF. But the standard here is 9 or 12 mm thickness, instead of the 10 mm in your fabrication drawings. I would prefer 12 mm. Will it work? (I know it's mentioned somewhere in the thread. I read it some months ago, but can't find it again).

In your thesis, I found what's meant with the diffusion coefficient ("high value indicate that a surface scatters sound uniformely to all receivers"). But what's the difference with the scattering coefficient and the normalized diffusion coefficient? Which one prevails when you look at the AFMG Reflex-graphics for judging a layout?


Thanks for info,
guido
Old 5th April 2017 | Show parent
  #752
Gear Addict
 
Arqen's Avatar
 
🎧 5 years
Front wall absorption

Quote:
Originally Posted by petergel ➡️
Sorry, I don't understand. What do you mean by place the diffuser over absorption? This diffuser weight 30Kg, I think it would be impossible to hang it in front of an absorptive panel.

My floor is reflective (tiles) so there’s nothing to remove. I thought that front wall give strong reflections and it’s very critical to cover it entirely. You believe it’s not critical?
I mean if it was constructed on a frame with absorption underneath, so that it doubles as a bass absorber.

Most speakers are highly directional at mid-high frequencies. I.e, they direct most of that energy forward. The main consideration on the front wall is bass frequencies, which can be managed with speaker placement, and thoughtfully-applied absorption if necessary (it requires some calculations, explained in my article here).

Whether or not you need front wall absorption depends on many things like speaker off-axis response, distance to the wall, low frequency cuttoff, how other surfaces in your room are treated, and the decay times in your room.

In general, it's not necessary. E.g., look at the control room in Abbey Road Studios shown below: free-standing monitors in front of glass windows.

But, I've written articles on it here to explain the various options:


Last edited by Arqen; 5th April 2017 at 09:37 AM..
Old 5th April 2017 | Show parent
  #753
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🎧 5 years
Quote:
Originally Posted by beetof ➡️
Hi Tim,

I'm trying to improve the acoustics of our living room.
On a mantelpiece, I want to add a A1-LF diffuser (just two elements, total width 84 cm), made of MDF. But the standard here is 9 or 12 mm thickness, instead of the 10 mm in your fabrication drawings. I would prefer 12 mm. Will it work? (I know it's mentioned somewhere in the thread. I read it some months ago, but can't find it again).

In your thesis, I found what's meant with the diffusion coefficient ("high value indicate that a surface scatters sound uniformely to all receivers"). But what's the difference with the scattering coefficient and the normalized diffusion coefficient? Which one prevails when you look at the AFMG Reflex-graphics for judging a layout?


Thanks for info,
guido
Hi Guido,

Yes, you can use 12 mm. It's explained in the FAQ here. I still need to get around to updating the plans.

Pay attention to the normalized diffusion coefficient.

In a nutshell, diffusion represents the uniformity of scattering. An ideal diffuser would spread energy uniformly in space and time, but current diffusion coefficient standards just focus on uniform scattering in space. For the perfect diffuser in the perfect world, this would result in a diffusion coefficient of 1 at all frequencies.

The difference between scattering and diffusion coefficients is explained in more detail in this paper by RPG. See the "scattering vs diffusion" section.
Old 11th April 2017 | Show parent
  #754
Here for the gear
 
Thank you for the info.

In fact I'm wondering also if a diffuser of only two elements will make much sense. I only see esthetical reasons. You can make something nice of them indeed.
How about the height? All your diffusers are 60 or 120 cm high. Any inconvenience for a height of say 90cm? Or slats of different lenght?
At one side of the mantelpiece is a big absorber of 250x136x18cm. On the other side I'm still going to make another small one.
Old 16th April 2017
  #755
Here for the gear
 
Hello everyone!
May be i'm not so competent in a diffusion physics, but wanna asking a question.

Can i use this rail-posts to construct A1-LF?

Of Course, i will multiply "depth/width" to achieve initial ratio. (rail-posts are 4.5 and 9 cm wide, not 6 cm like in an A1-LF desigh.)

This round shape can make some great HF diffusion, isn't it?
Attached Thumbnails
DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-dscn5982.jpg   DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-dscn5980.jpg  
Old 16th April 2017
  #756
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6 Reviews written
🎧 10 years
What about the bookshelf diffuser?
Old 18th April 2017 | Show parent
  #757
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🎧 5 years
Quote:
Originally Posted by beetof ➡️
Thank you for the info.

In fact I'm wondering also if a diffuser of only two elements will make much sense. I only see esthetical reasons. You can make something nice of them indeed.
How about the height? All your diffusers are 60 or 120 cm high. Any inconvenience for a height of say 90cm? Or slats of different lenght?
At one side of the mantelpiece is a big absorber of 250x136x18cm. On the other side I'm still going to make another small one.
It depends how close they are to you. Generally you need some decent surface area coverage to notice a difference. But if you have big absorbers with blank spaces between / around them, diffusers are better than bare wall in those spaces. Unless a specular reflection is desired, diffusers are going to be better than bare wall.

The height is flexible, so 90 cm is fine. Using slats of different length will alter the performance at the end points as the geometry changes, but might look cool. I’d say it’s worth doing if it’s an aesthetic you’re looking for.
Old 18th April 2017 | Show parent
  #758
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🎧 5 years
Quote:
Originally Posted by TTRESHH ➡️
Hello everyone!
May be i'm not so competent in a diffusion physics, but wanna asking a question.

Can i use this rail-posts to construct A1-LF?

Of Course, i will multiply "depth/width" to achieve initial ratio. (rail-posts are 4.5 and 9 cm wide, not 6 cm like in an A1-LF desigh.)

This round shape can make some great HF diffusion, isn't it?
Interesting approach.

Yes, the rounded shape will produce great high frequency diffusion. It will certainly be a useful surface, but such a departure from the original geometry that it would be like an entirely different design that we don’t have performance data for.

This is a case where I think we can trust intuition. The complexity is so high that even without measurements, I expect it to create a scattered sound field that’s uniform enough to call diffusion.

With all the air passages there will be extra losses, but this shouldn't be a big deal. Possible resonance from internal reflections doesn't concern me here, as the rounded surfaces would diffuse those internal reflections.
Old 18th April 2017 | Show parent
  #759
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🎧 5 years
Bookshelf diffuser

Quote:
Originally Posted by philsaudio ➡️
What about the bookshelf diffuser?
A bookshelf can act as anything from a reflective surface to a diffuser, depending on the size of bookself, size of books, and how those books are arranged.

Let’s say we compare random vs diffusion-optimized surfaces with similar geometric parameters (size, complexity, depth variation, width of each element, etc).

When the surfaces are small, the surface optimized for diffusion (uniform scattering) dominates. An intuitive way to think of it is that it’s easy for a small, random surface to be lopsided, creating a lopsided scattering pattern. But as the surfaces get very large and complex, the random surface starts to approach the performance of the optimized surface.

E.g., if it was a huge library wall filled with glossy books, with the surface depth of books varying by 5 inches, and the listener is sitting 30 feet away, it may be comparable to a purpose-designed diffusive wall.

But if the bookshelf is, say, 2 feet wide, it won’t have comparable performance to a 2 foot wide optimized diffuser of comparable complexity and geometry.

Also, a bookshelf may add more absorption than a purpose-designed diffuser.
Old 20th April 2017 | Show parent
  #760
Gear Nut
 
🎧 5 years
Quote:
Originally Posted by Arqen ➡️
Hi Peter,

Normally I recommend 1D diffusers on the rear wall. But, since you don't have much space behind you, you're better off with 2D PRD (skyline-style) diffusers that reduce the energy returned to the listening position. Of those two choices I would choose their Manhattan diffuser for your specific case.

Hi Tim,

I suppose I’ll need at least 4 Manhattan diffusers or even better 6 of them to cover the rear wall to have a decent diffusion effect. Pricing will vary from 680.00€ to 1020.00€, that’s a lot of money for my wallet.
I’m thinking the DIY options. What diffuser from your DIY designs would you recommend for my case?
As I said before the distance between my listening position and my rear wall is 180cm and I may be able to make it 200cm.
Old 22nd April 2017
  #761
Gear Maniac
 
🎧 10 years
Quote:
Originally Posted by Arqen ➡️
[Click here to get the DIY Diffuser Blueprints]

Hey guys,

You might recall that I was going to give away free blueprints for DIY sound diffusers.

Well, here they are:


DIY Sound Diffuser Blueprints <- Free Fabrication Drawings








ABOUT THE OPTIMIZED DIY STEPPED DIFFUSERS

These are low profile, optimized stepped diffusers, designed for my thesis on acoustic diffuser optimization (outlined in this thread).

These modular DIY diffusers strike an optimal balance between
  • Performance (designed using simulated natural selection and physical modeling)
  • Compactness (low profile, modular design)
  • Simplicity (easy to construct)


At least two people have built the diffusers so far and were excited to tell me that they were cheap and simple to make — Exactly what I intended! Those folks constructed the diffusers using the information in the thesis… but because you have access to the blueprints, you should have an even easier time building them!



FRACTAL DIFFUSERS

For those of you who are interested in building fractal sound diffusers, I’ll include fractal diffuser specs in the near future [Update: specs for one of the fractal diffusers are now available for download]. I’ll keep you up to date if you follow this thread or sign up for updates on my website. In the meantime, you’ll find the dimensions for all the diffusers in the diffuser design thesis.



The video above shows a simulation of sound scattering from a fractal acoustic diffuser (finite difference time domain (FDTD) simulation).



THE DIY DIFFUSER BLUEPRINTS

To grab the designs, visit the link below.

DIY Sound Diffusers <- Free Blueprints



ARE YOU COMFORTABLE BUILDING THEM?
WHAT CHALLENGES DO YOU FACE?


I hope you guys like the designs. Please reply to this thread if you have any questions, insights, run into any challenges while building them, etc.

Also, I’d like to know:
  1. Do you think the stepped diffusers look easy to build?
  2. Where do you live?
  3. Do you have access to 1cm thick construction material? Or do you only have access to lumber with imperial dimensions?
  4. Do you have access to affordable bamboo lumber?
  5. What’s the most likely material you’d use for building them?
  6. What tools are available to you? Do you have access to woodworking equipment? CNC?



Enjoy the blueprints!

Tim

P.S. I’ll update this thread when I post more DIY diffuser resources. So stay tuned!
(to download the designs, visit the blue link above)

Tim,

I have studied your Thesis and that is fantastic treatment of optimization process and this was hard work I suppose.
I have made severals Peter DÁntonio and Trevor Cox diffuser and this is a lot of work!!.....your Thesis is a great more simple workmanship work and according to your data, great performance too all this in a low profile fashion.

Because this theme is another whole word and ideas day to day, Do you have an update of this kind of work?

Thanks and I appreciate your effort and work in this very new theories and no to easy at all!
Opacheco.
Old 23rd April 2017 | Show parent
  #762
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🎧 5 years
Quote:
Originally Posted by opacheco ➡️
Tim,

I have studied your Thesis and that is fantastic treatment of optimization process and this was hard work I suppose.
I have made severals Peter DÁntonio and Trevor Cox diffuser and this is a lot of work!!.....your Thesis is a great more simple workmanship work and according to your data, great performance too all this in a low profile fashion.

Because this theme is another whole word and ideas day to day, Do you have an update of this kind of work?

Thanks and I appreciate your effort and work in this very new theories and no to easy at all!
Opacheco.
Hi Opacheco,

Glad you appreciate it. It's not my current focus as there are other projects I'm working on, but I've been looking into ways to make construction easier. Moving to standard lumber dimensions as the standard units to optimize for, etc.

I initially left a lot open to interpretation to allow for open-source innovation. Updated best practices are french cleats for mounting and a 12 mm step size (mentioned in the FAQ but not yet updated in the drawings as I've been very busy). The current hurdle is mounting complexity given the depth modulations (aka profiled modulations).

There is still no clearly defined "best way" of doing the mounting, and there are dangers associated with posting a mounting method that people may wrongly interpret.

Best practice for mounting tends to involve a french cleat, but the best way of integrating that french cleat into a riser system to lift the diffusers off the wall is still open to interpretation. I drew up what I thought was the simplest solution for a client, but the carpenter who built it chose a radically different approach, so we did not get a real world test. Several carpenters have built it, and each implemented it differently.

If and when we run into the holy grail of mounting, I will add it to a new version of the plans. Most methods to date are either complicated (building risers containing french cleats), or not sufficiently safe.

While the A1 designs (aka Leanfuser / Leanfractal) are super simple in their basic geometry, the requirement for mounting at different depths for the best performance adds a level of complexity that does not work for everyone.

Two solutions to this are Barker Modulations, or different designs with asymmetry (like the B2 design). But both these solutions involve increasing the construction complexity of the individual modules, and these have inferior performance to the depth-modulated A1 designs.

It's a balancing act with many parameters.
Old 23rd April 2017 | Show parent
  #763
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Arqen's Avatar
 
🎧 5 years
Smile

Quote:
Originally Posted by petergel ➡️
Hi Tim,

I suppose I’ll need at least 4 Manhattan diffusers or even better 6 of them to cover the rear wall to have a decent diffusion effect. Pricing will vary from 680.00€ to 1020.00€, that’s a lot of money for my wallet.
I’m thinking the DIY options. What diffuser from your DIY designs would you recommend for my case?
As I said before the distance between my listening position and my rear wall is 180cm and I may be able to make it 200cm.

It depends how important critical listening is to you. Most diffusers are simply not tested at those distances, but the Leanfuser was optimized at a radius of 2.5 meters, which is not far off.

For many people the Leanfuser is fine at those distances, based on reports from the many people who have used them close up. I've had no reports of audible artifacts. But technically, to avoid blasphemy against the acoustic gods the safer approach is to use something focused on higher frequencies, or that returns less energy to the listener. Examples are these DIY PRD diffusers, the Leanfractal, or a shrunk version of the Leanfuser so that it focuses on higher frequencies (all dimensions scaled by 0.75 or 0.5).

Many designers would never put diffusers that close, and use absorption instead. Others do it all the time, or use hybrid devices. There is so little consensus for a variety of reasons:

- Diffuser designs vary.
- Many people working in the acoustics industry preach pseudoscience/voodoo.
- Lack of universally accepted (or known) psychoacoustic test data means many acousticians default to the theoretical minimum listening distance of 3 times the lowest wavelength diffused, or typically about 3 meters. This is the safest way to go.
- Listening is largely subjective, people have different goals, and even those with similar goals have different tolerance levels for what they consider acceptable.

I view it in terms of the listening goals, and I only use diffusers up close if they are focused on higher frequencies.

As you can see, when we're in this grey zone without hard performance data, the choice of diffuser type (or no diffuser at all) is largely subjective.
Old 25th April 2017 | Show parent
  #764
Gear Nut
 
🎧 5 years
Quote:
Originally Posted by Arqen ➡️
It depends how important critical listening is to you. Most diffusers are simply not tested at those distances, but the Leanfuser was optimized at a radius of 2.5 meters, which is not far off.

For many people the Leanfuser is fine at those distances, based on reports from the many people who have used them close up.
Thank you Tim, I think I'll go with Leanfuser. What type of wood do you suggest besides MDF? I do not wnat to use MDF becuase of its high formaldehyde levels.


Quote:
Originally Posted by Arqen ➡️
Many designers would never put diffusers that close, and use absorption instead. Others do it all the time, or use hybrid devices. There is so little consensus for a variety of reasons.

I view it in terms of the listening goals, and I only use diffusers up close if they are focused on higher frequencies.
Being higher or lower frequencies I believe it would be better than a flat bare wall, right? I mean, is there a possibilitynot to like the sound at the sweetsport after placing the Leanfusers or 2D skyline diffuser?


EDIT: In the video below, a user (Proiectediversediy) comment that it's better to use soft wood because hard wood is absorbing more frequencies. Is this true? I thought the opposite is correct. https://www.youtube.com/watch?v=oHTmNyo_0O0
Old 26th April 2017 | Show parent
  #765
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🎧 5 years
Quote:
Originally Posted by petergel ➡️
Thank you Tim, I think I'll go with Leanfuser. What type of wood do you suggest besides MDF? I do not wnat to use MDF becuase of its high formaldehyde levels.

The sky is the limit for wood types. The wood type has negligible effect on acoustics. Weight, cost, appearance, workability and durability are all things to be considered, and different people prioritize different things. I've seen nice diffuser built from plywood, MFD, cheap softwood lumber like spruce, all kinds of hardwood lumber (watch the weight here), even sheet metal.

A cabinet making site would be a good place for wood ideas. You could also check out the wide range of woods RPG is using.

Quote:
Being higher or lower frequencies I believe it would be better than a flat bare wall, right? I mean, is there a possibilitynot to like the sound at the sweetsport after placing the Leanfusers or 2D skyline diffuser?
I've never encountered it, but there's a possibility someone might not like the sound if they are sitting very close and the diffuser is causing phasey sounding artifacts. But, I've yet to experience a case where a diffuser is worse than a bare wall.

Quote:
EDIT: In the video below, a user (Proiectediversediy) comment that it's better to use soft wood because hard wood is absorbing more frequencies. Is this true? I thought the opposite is correct. https://www.youtube.com/watch?v=oHTmNyo_0O0
You're absolutely right. It's not true. Absorption is caused mostly by the roughness / complexity of the surface, width and depth of the wells, finish, and to some extent the density / stiffness / hardness. If anything, hardwood should be more reflective, but I doubt anyone would notice the difference in sound between hardwood and softwood diffusers.

A hard, varnished surface is better in theory. The opposite of what he said.
Old 26th April 2017 | Show parent
  #766
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Bstapper's Avatar
 
🎧 5 years
Quote:
Originally Posted by Arqen ➡️
Hi Opacheco,

Glad you appreciate it. It's not my current focus as there are other projects I'm working on, but I've been looking into ways to make construction easier. Moving to standard lumber dimensions as the standard units to optimize for, etc.

I initially left a lot open to interpretation to allow for open-source innovation. Updated best practices are french cleats for mounting and a 12 mm step size (mentioned in the FAQ but not yet updated in the drawings as I've been very busy). The current hurdle is mounting complexity given the depth modulations (aka profiled modulations).

There is still no clearly defined "best way" of doing the mounting, and there are dangers associated with posting a mounting method that people may wrongly interpret.

Best practice for mounting tends to involve a french cleat, but the best way of integrating that french cleat into a riser system to lift the diffusers off the wall is still open to interpretation. I drew up what I thought was the simplest solution for a client, but the carpenter who built it chose a radically different approach, so we did not get a real world test. Several carpenters have built it, and each implemented it differently.

If and when we run into the holy grail of mounting, I will add it to a new version of the plans. Most methods to date are either complicated (building risers containing french cleats), or not sufficiently safe.

While the A1 designs (aka Leanfuser / Leanfractal) are super simple in their basic geometry, the requirement for mounting at different depths for the best performance adds a level of complexity that does not work for everyone.

Two solutions to this are Barker Modulations, or different designs with asymmetry (like the B2 design). But both these solutions involve increasing the construction complexity of the individual modules, and these have inferior performance to the depth-modulated A1 designs.

It's a balancing act with many parameters.
Use magnets? You could use magnet washers that would allow you to sheet rock anchor magnets to the wall and screw magnets to the panels?

You can get them in literally any shape, strength, and countersunk such as this:
http://www.ebay.com/itm/5-100pcs-N52...0N9akzhUPVCJGg

Anyway - thank you for this. Exciting!

Cheers,
Brock
Old 15th May 2017 | Show parent
  #767
Here for the gear
 
🎧 5 years
Hello,

I'm trying to put together the right measurements of wood to make the Leanfuser (Imperial) and I came across these pieces of wood.

They look fractal-ish. Anyone know if these would work well to have a kind of fractal-like effect?

Thanks!

Paul
Attached Thumbnails
DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-b1539b30-9b4e-41d0-a2e2-ec523b20887c_1000.jpg  
Old 21st May 2017
  #768
Gear Head
 
🎧 10 years
Hey Tim

Forgive me if this has been covered. I am almost done building poplar Leanfusors. I will post pics, theyre turning out great.

I built three modules. 2'x4'. How would you hang them. Would you protrude the middle one out a greater distance than the two side modules? Also would be wrong to put space between the modules (just for wall aesthetic symmetry)?

I saw the arrangements for 5 and 7 modules but not for 3. It's all I had room for on my back wall.
Old 7th June 2017
  #769
Lud
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🎧 5 years
New Sound Diffuser Is 10 Times Thinner Than Existing Designs

https://news.ncsu.edu/2017/06/thinne...diffuser-2017/
Old 7th June 2017 | Show parent
  #770
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🎧 10 years
I'd check the performance data and frequency range. Super sonic no doubt. I call BS.
Old 8th June 2017 | Show parent
  #771
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2 Reviews written
🎧 10 years
Quote:
Originally Posted by John White ➡️
I'd check the performance data and frequency range. Super sonic no doubt. I call BS.
Did you actually read the published paper before summarily dismissing it?
Old 8th June 2017 | Show parent
  #772
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🎧 10 years
Quote:
Originally Posted by kywoman ➡️
Did you actually read the published paper before summarily dismissing it?
Seriously. It's not some marketing bs but rather an academically published paper.

Looks interesting, but would say better off as it's own thread. Keep this one about the Arqen DIY diffuser.
Old 14th June 2017 | Show parent
  #773
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Arqen's Avatar
 
🎧 5 years
Quote:
Originally Posted by JesterPaul ➡️
Hello,

I'm trying to put together the right measurements of wood to make the Leanfuser (Imperial) and I came across these pieces of wood.

They look fractal-ish. Anyone know if these would work well to have a kind of fractal-like effect?

Thanks!

Paul
Hi Paul,

Sorry for the delay. They would have a fractal-like effect in that they would complexity the high frequency scattering. While they won't scatter as uniformly as an intentionally designed shape, I expect they will provide benefit. It's also worth noting that a simple concave or convex surface applied to each well will provide benefit, while being much simpler than a fractal design.
Old 14th June 2017 | Show parent
  #774
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🎧 5 years
Quote:
Originally Posted by Aram9012 ➡️
Hey Tim

Forgive me if this has been covered. I am almost done building poplar Leanfusors. I will post pics, theyre turning out great.

I built three modules. 2'x4'. How would you hang them. Would you protrude the middle one out a greater distance than the two side modules? Also would be wrong to put space between the modules (just for wall aesthetic symmetry)?

I saw the arrangements for 5 and 7 modules but not for 3. It's all I had room for on my back wall.
Yes, that's the right approach. See the FAQ here for 3-module configurations that have been tested.
Old 14th June 2017 | Show parent
  #775
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🎧 5 years
Quote:
It looks clever and very interesting, but the idea has been around for a while, and first tried in 1997 by Hunecke. Here is the best commentary on it, by Trevor Cox, one of the leading experts on diffusion: http://www.lydogakustikk.no/?p=2706&lang=nb.

First, my own thoughts: while I love the concept, one concern up front is friction losses from the viscous boundary layer within those narrow cavities. These losses may be fine in many applications, where a hybrid of absorption and is diffusion desired.

There's also the question of whether this compacted Schroeder-inspired device -- tantalizing in theory, as it would produce BOTH temporal and spatial scattering -- does in fact provide more complete diffusion than binary amplitude devices (BAD), which are even simpler in design and can be made thinner. Binary amplitude diffusers are only designed for uniform spatial scattering, but they do this very well, with a remarkably simple design. Unfortunately, these folded well diffusers can't compete with BAD panels at high frequencies.

Here's the big pitfall of the design, as mentioned by Cox: "The real problem is that the performance at high frequency suffer if every well is replaced by a Helmholtz resonator. When the wavelength gets small compared to the spacing between the holes in Figure 2, then you get a strong reflection from the flat front surface. You can see the decreased performance at the highest frequencies tested in the paper on arxiv.org (see Figure 5 for example). I can think of no application where it would be good for a diffuser to stop working at high frequency, because that is the bandwidth where perceptual aberrations are most prominent. That is why when we sketched Figure 10.30 [RPG QRD with only some wells folded] we kept some of the wells as conventional 1/4 wave resonators."

Last edited by Arqen; 14th June 2017 at 08:56 PM..
Old 14th June 2017 | Show parent
  #776
Lud
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🎧 5 years
Quote:
Originally Posted by Arqen ➡️
It looks clever and very interesting, but the idea has been around for a while, and first tried in 1997 by Hunecke. Here is the best commentary on it, by Trevor Cox, one of the leading experts on diffusion: Schroeder diffuser using a metasurface: new idea? | Lyd & Akustikk.

First, my own thoughts: while I love the concept, one concern up front is friction losses from the viscous boundary layer within those narrow cavities. These losses may be fine in many applications, where a hybrid of absorption and is diffusion desired.

There's also the question of whether this compacted Schroeder-inspired device -- tantalizing in theory, as it would produce BOTH temporal and spatial scattering -- does in fact provide more complete diffusion than binary amplitude devices (BAD), which are even simpler in design and can be made thinner. Binary amplitude diffusers are only designed for uniform spatial scattering, but they do this very well, with a remarkably simple design. Unfortunately, these folded well diffusers can't compete with BAD panels at high frequencies.

Here's the big pitfall of the design, as mentioned by Cox: "The real problem is that the performance at high frequency suffer if every well is replaced by a Helmholtz resonator. When the wavelength gets small compared to the spacing between the holes in Figure 2, then you get a strong reflection from the flat front surface. You can see the decreased performance at the highest frequencies tested in the paper on arxiv.org (see Figure 5 for example). I can think of no application where it would be good for a diffuser to stop working at high frequency, because that is the bandwidth where perceptual aberrations are most prominent. That is why when we sketched Figure 10.30 [RPG QRD with only some wells folded] we kept some of the wells as conventional 1/4 wave resonators."


So it says it works for low freqs and not for the high freqs. We can imagine mixing "ultra-thin" diffusers for the lows that will take less space and keep using conventional Schroeder diffusers for the high freq? also i guess the ultra thin are more complicated to make for diy.
Old 16th June 2017
  #777
Gear Head
 
🎧 10 years
Thank you so much Tim! I got em on the wall and I think they came out great. I've gotten some compliments already the design is the most aesthetically sharp diffusor I've ever seen.

I had mounted them last week so I didn't see the post. I just came up with number that felt right based on the protrusions of the 5 & 7 panel setups, and protruded mine by 2 inches.

The other thing I did in case ppl are interested to reduce weight and material a bit is used a split up back panel instead of the continuous one which would've been the biggest piece of wood in the assembly. The only downside to this I imagine is less surface area to use for mounting, but it worked out fine. I used mirror/picture Z hangers from Amazon to hang.
Attached Thumbnails
DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-img_1118.jpg   DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-img_0983.jpg  
Old 17th June 2017 | Show parent
  #778
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by Aram9012 ➡️
Thank you so much Tim! I got em on the wall and I think they came out great. I've gotten some compliments already the design is the most aesthetically sharp diffusor I've ever seen.

I had mounted them last week so I didn't see the post. I just came up with number that felt right based on the protrusions of the 5 & 7 panel setups, and protruded mine by 2 inches.

The other thing I did in case ppl are interested to reduce weight and material a bit is used a split up back panel instead of the continuous one which would've been the biggest piece of wood in the assembly. The only downside to this I imagine is less surface area to use for mounting, but it worked out fine. I used mirror/picture Z hangers from Amazon to hang.
Nice work. What kind of wood did you use for these?
Old 17th June 2017 | Show parent
  #779
Gear Addict
 
Arqen's Avatar
 
🎧 5 years
Quote:
Originally Posted by Lud ➡️
So it says it works for low freqs and not for the high freqs. We can imagine mixing "ultra-thin" diffusers for the lows that will take less space and keep using conventional Schroeder diffusers for the high freq? also i guess the ultra thin are more complicated to make for diy.
Exactly. RPG does this for a couple of their designs (I forget which ones, and their site is down now). They're not ultra thin, but they have folded wells for lower frequencies, making them significantly thinner than they would otherwise need to be.
Old 17th June 2017 | Show parent
  #780
Gear Addict
 
Arqen's Avatar
 
🎧 5 years
Quote:
Originally Posted by Aram9012 ➡️
Thank you so much Tim! I got em on the wall and I think they came out great. I've gotten some compliments already the design is the most aesthetically sharp diffusor I've ever seen.
Nice work. They look great!
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