DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)
Arqen
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22nd September 2012
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DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)

[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)
Attached Thumbnails
DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-diffuser-a1-lf-module-2-w1024.jpg   DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-diffuser-a1-lf-module-tall-section-w1024.jpg   DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-diffuser-a1-lf-module-tall-2-w1024.jpg   DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-diffuser-a1-lf-module-tall-1-w1024.jpg   DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-diffuser-b2-fractal-module-solid1-w1024.jpg  

DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-diffuser-b2-fractal-module-solid2-w840x840.jpg   DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-diffuser-b2-fractal-solid2-w1024.jpg   DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-diffuser-a1-lf-fab-w480.jpg   DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-diffuser-a1-lf-fab-2-w480.jpg   DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-sound-diffuser-calage2-w1024.jpg  

Attached Images
File Type: jpg module-a1-lf-bem-0-0deg-w1024.jpg (85.9 KB, 1225 views) File Type: jpg a1-lf-bem-0-0deg-w1024.jpg (92.6 KB, 865 views) File Type: jpg a1-lf-modulate-diffusion-w1024.jpg (48.7 KB, 854 views) File Type: png fdtd-sim-fractal-diffusers.png (865.5 KB, 1543 views)

Last edited by Arqen; 22nd September 2012 at 06:47 PM.. Reason: Typo
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22nd September 2012
Old 22nd September 2012
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Fantastic information and free is my favorite price.

Thank You,
Arqen
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23rd September 2012
Old 23rd September 2012
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Quote:
Originally Posted by John White View Post
Fantastic information and free is my favorite price.

Thank You,
You're very welcome John!

Also, they're quite cheap to build (one of the cheapest options I know of is to use 1cm thick fiber board).
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23rd September 2012
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Can the dimensions be changed in proportion? In other words, can the one's be two's and the two's four's, etc...so that it can be changed easier to imperial measurements and accessible materials?

Also, other than the "mounting modules" can periodicity be addressed through inverse panels?
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23rd September 2012
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Aperiodic modulation for acoustic diffusers

Quote:
Originally Posted by John White View Post
Can the dimensions be changed in proportion? In other words, can the one's be two's and the two's four's, etc...so that it can be changed easier to imperial measurements and accessible materials?

Also, other than the "mounting modules" can periodicity be addressed through inverse panels?
Good questions!

If you scale the dimensions the performance will change. While it will still function as a diffuser, I don't know if the performance will be satisfactory. The easiest way to tell would be to test it using AFMG Reflex software. (My demo of the software has expired, but if I install it on another machine any time soon I'll try that simulation. Until then, maybe someone else who has AFMG Reflex would like to try simulating it?).

Aperiodic Modulation
Regarding inverse mounting: I actually optimized the designs in an aperiodic array, modulated using the sequence {1 0 1 1 0}. But during optimization the lowest profile design (called A1-LF) converged to be symmetrical... therefore, whether you reverse the modules or not, it's periodic. In other words, the best solution found by the algorithm (optimization combined with a phyisal model) was a symmetrical diffuser module.

The other stepped diffuser design mentioned in the thesis (called B2-LF) is not symmetrical, and is therefore aperiodic (because it's modulated with the sequence 1 0 1 1 0). While the aperiodic designs offer better performance, they are more complex in shape and deeper in profile.

Because the aperiodic designs are less elegant, they are less suitable as DIY diffusers. I did not create detailed blueprints for them, but if you wish to build them, the specs are in Chapters 7.3 and Chapter 8 of the thesis.


Optimizing for both Depth and Performance
I should clarify that I was optimizing for depth, not simply performance.

The low profile, symmetrical design (A1-LF) was optimized to have good performance, while being super low profile.

The asymmetrical design (B2-LF) achieved better performance, but with a deeper depth.


Hope I'm not being too confusing. Does that make sense to you?

-Tim
#6
23rd September 2012
Old 23rd September 2012
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Thank you so much for this Tim.

Good timing for me as I am looking for a suitable diffusor for my newly finished control room rear wall. My goal is to try and keep the room somewhat live.

The rear wall has 14 inches of absorption across the full area. The room height would not allow a array as depicted in your blueprints, so Im thinking of three or four side by side across the wall.

You mention the trade off of performance v cost and ease of build quite often. How would the stepped diffusor hold up against a more traditional QRD design as far as performance goes?

Also, what would be the minimum distance to be from one of these designs? I have around 10ft from mix position to the rear wall. thanks again
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23rd September 2012
Old 23rd September 2012
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23rd September 2012
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Quote:
Originally Posted by Jens Eklund View Post
Thanks for pointing those out Jens.

I've since posted updated performance simulations using AFMG Reflex at the bottom of the page here:

http://arqen.com/sound-diffusers/#coefficients

If you want more detailed performance reports (performance for other optimized diffusers, various angles of incidence, etc), you can download them from my website (see the link above).

You get free access to all the detailed performance reports in the diffuser designs download vault.

Cheers,

Tim
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23rd September 2012
Old 23rd September 2012
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Thanks again Tim-

How does the total area of the diffusors correlate to the prediction models? In other words, if one wanted to match the low frequency diffusion as modeled in the software, how large (height/width) would the units have to be?

Edit: I see Jens has answered some of this in the link. Does this include height?
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Quote:
Originally Posted by John White View Post
How does the total area of the diffusors correlate to the prediction models? In other words, if one wanted to match the low frequency diffusion as modeled in the software, how large (height/width) would the units have to be?
When measuring or predicting scattering and diffusion coefficients, one needs to measure (or model) a big enough surface (more than one period) or the values given will be very high and mean nothing. An empirically derived limit states that the total width of the sample needs to be at least 16 times longer than the total structural depth. A common total panel width used is 3,6 meters (as in the appendix of Acoustic Absorbers and Diffusers).


Edit: The height of the sample is irrelevant assuming 1D diffusers since we´re only concerned with the scattering in the operational plane of the diffuser.
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23rd September 2012
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Quote:
Originally Posted by Jens Eklund View Post
Edit: The height of the sample is irrelevant assuming 1D diffusers since we´re only concerned with the scattering in the operational plane of the diffuser.
Thanks Jens. I still don't understand, however. By that logic it would seem that it would disuse down to the same frequency regardless of the height. Certainly it would correlate to some degree the size of the wave lengths?

Great thread.
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23rd September 2012
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We are naturally assuming that any dimension (except depth) of the panel is large compared to the wavelength considered but yes, the total geometry of the devise will cause some scattering in the other plane as well but in order to simulate the effect of it, you would need a model that can predict the scattering of 2D diffusers.
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23rd September 2012
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Quote:
Originally Posted by dodittydada View Post
Thank you so much for this Tim.

Good timing for me as I am looking for a suitable diffusor for my newly finished control room rear wall. My goal is to try and keep the room somewhat live.

The rear wall has 14 inches of absorption across the full area. The room height would not allow a array as depicted in your blueprints, so Im thinking of three or four side by side across the wall.

You mention the trade off of performance v cost and ease of build quite often. How would the stepped diffusor hold up against a more traditional QRD design as far as performance goes?

Also, what would be the minimum distance to be from one of these designs? I have around 10ft from mix position to the rear wall. thanks again
Hi Tim,

No problem!

I've not tested the performance of 3 or 4 modules. The diffusers were optimized in an array of 5, but I believe they will still be useful in a smaller array (the easiest way to know would be to simulate it using Reflex).

I've not done a direct performance comparison against a QRD, but I have done a direct comparison with other optimized stepped diffusers that perform better than QRDs. If you scroll down in the download area, you'll see performance reports for deep (15cm operational depth) stepped diffusers optimized by T.J. Cox (co-author of the book "Acoustic Absorbers and Diffusers").

If you download the performance reports for "5 Periods of Deep N = 7 Stepped Diffuser" and compare them to the performance reports for A1-LF (which has a 5 cm operational depth), you'll see that the low profile designs are surprisingly effective given how shallow they are. While the average coefficient is lower compared with the 15cm+ deep N=7 stepped diffuser, A1-LF has a more even diffusion coefficient spectra (with a total depth of 6cm, and an operational depth of only 5cm).

Also, If you look at the performance coefficients for "Modulated Array A1-LF", you'll see that with an 11 cm operational depth this configuration performs better than 5 periods of Cox's N=7 stepped diffusers (15 cm operational depth).

FTY, when I say "15cm+" I mean the operational depth is 15 cm, but the actual diffuser is deeper when the depth of the base is included.

Hope this helps!

- the other Tim
#14
24th September 2012
Old 24th September 2012
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Great thread.

Guys can someone please explain what happens when diffusion goes in front of a fully absorbed back wall? Does bass that is below the cutoff of the diffusor just wrap around it and continue on to be absorbed as normal, as if the diffusor wasn't even really there ? Thanks.
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24th September 2012
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Originally Posted by Radial185 View Post
Great thread.

Guys can someone please explain what happens when diffusion goes in front of a fully absorbed back wall? Does bass that is below the cutoff of the diffusor just wrap around it and continue on to be absorbed as normal, as if the diffusor wasn't even really there ? Thanks.
That's a great question. Yes, but the effectiveness will vary depending on the type of absorption... the performance of the low frequency absorption may be altered because the angle of the incident wave will change as it wraps around the diffuser.

Here is a link explaining edge scattering, reflection and diffraction when sound hits a plane surface.

I'm assuming that the base of the diffuser (e.g. the back board for mounting on the wall) is a plane surface.

For this plane surface the cutoff frequency marks the transition between specular reflection and diffraction (diffraction is the breaking up of wavefronts due to edges).

As you can see from the images below, diffraction occurs at the edges of the surface and results in a wrap-around effect.





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24th September 2012
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So, assuming I could find some EPS for a good price, how practical would a build from EPS be on this diffuser?

If someone could or would model it, could we change this and see if the performance drops heavily?
Depth units based on 1/2" instead of 10mm (12.7mm instead of 10mm)
Depth units based on 3/8" instead of 10mm (9.525mm instead of 10mm)

I can't find anything thinner than 0.5" at Home Depot or Lowes, but I could probably order 3/8" EPS from an HVAC supplier I would imagine. Since 3/8" translates to 9.525mm which is much closer to the design spec, I assume it to be closer, but not sure if this is really the way diffusion works. (But then its slightly thinner, so I'm not sure if that would in turn make it worse where making it deeper wouldn't be so bad?)

I can obviously cut them myself to metric widths, so that part isn't a really bad deal.

Also, I modeled it in Sketchup in the Profiled Modulation 1 array. Tim, I figured you would be pleased if I posted it here so I will. Of course you can distribute it at will. If you'd like me to take it down for any reason let me know.

Edit: I can't wait for the B2!
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24th September 2012
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Quote:
Originally Posted by kasmira View Post
So, assuming I could find some EPS for a good price, how practical would a build from EPS be on this diffuser?

If someone could or would model it, could we change this and see if the performance drops heavily?
Depth units based on 1/2" instead of 10mm (12.7mm instead of 10mm)
Depth units based on 3/8" instead of 10mm (9.525mm instead of 10mm)

I can't find anything thinner than 0.5" at Home Depot or Lowes, but I could probably order 3/8" EPS from an HVAC supplier I would imagine. Since 3/8" translates to 9.525mm which is much closer to the design spec, I assume it to be closer, but not sure if this is really the way diffusion works. (But then its slightly thinner, so I'm not sure if that would in turn make it worse where making it deeper wouldn't be so bad?)

I can obviously cut them myself to metric widths, so that part isn't a really bad deal.

Also, I modeled it in Sketchup in the Profiled Modulation 1 array. Tim, I figured you would be pleased if I posted it here so I will. Of course you can distribute it at will. If you'd like me to take it down for any reason let me know.

Edit: I can't wait for the B2!

Big thanks for drawing up the modulated array! I'm sure people will find that useful for visualizing the design.

I expect expanded polystyrene would work, but the end result might be frail.The main reason I'm not big on that material is that it takes forever to degrade and most places (so far as I know) don't recycle it.

Thanks for your ideas on the imperial options! I'll make a note to simulate imperial versions of the design when I have a bit of down time in the future... In the meantime, if anyone wants to play around with design variations, AMFG Reflex acoustics simulation software has a demo version (my demo of Reflex software has expired).
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24th September 2012
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Quote:
Originally Posted by Arqen View Post
Big thanks for drawing up the modulated array! I'm sure people will find that useful for visualizing the design.

I expect expanded polystyrene would work, but the end result might be frail.The main reason I'm not big on that material is that it takes forever to degrade and most places (so far as I know) don't recycle it.

Thanks for your ideas on the imperial options! I'll make a note to simulate imperial versions of the design when I have a bit of down time in the future... In the meantime, if anyone wants to play around with design variations, AMFG Reflex acoustics simulation software has a demo version (my demo of Reflex software has expired).
Thanks Tim.

It is a true about EPS not being a very friendly material - however, I don't plan on throwing away any diffuser I build for quite some time

I did just send in a form to get a copy of Reflex for trial. If I'm able to figure it out well enough, I'll post the results in here.
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25th September 2012
Old 25th September 2012
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Originally Posted by kasmira View Post
Thanks Tim.

It is a true about EPS not being a very friendly material - however, I don't plan on throwing away any diffuser I build for quite some time

I did just send in a form to get a copy of Reflex for trial. If I'm able to figure it out well enough, I'll post the results in here.

Great! There are all kinds of possibilities for mounting the modules that have not yet been simulated, so it would be interested to see what people can come up with.

Reflex is quite easy to use and very useful. I wish I had know about it earlier.

While Reflex would not have helped optimize the diffuser modules, it's very useful for verifying results and testing design tweeks.
(Geek moment: to optimize the diffusers I needed to code a design system, and part of it was a "finite difference time domain" scattering model. One reason Reflex is useful now is because it can be used to verify that my optimization system produces valid results)

Thanks for taking such a proactive interest in this!

Tim
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25th September 2012
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Quote:
Originally Posted by kasmira View Post
So, assuming I could find some EPS for a good price, how practical would a build from EPS be on this diffuser?

If someone could or would model it, could we change this and see if the performance drops heavily?
Depth units based on 1/2" instead of 10mm (12.7mm instead of 10mm)
Depth units based on 3/8" instead of 10mm (9.525mm instead of 10mm)

I can't find anything thinner than 0.5" at Home Depot or Lowes, but I could probably order 3/8" EPS from an HVAC supplier I would imagine. Since 3/8" translates to 9.525mm which is much closer to the design spec, I assume it to be closer, but not sure if this is really the way diffusion works. (But then its slightly thinner, so I'm not sure if that would in turn make it worse where making it deeper wouldn't be so bad?)

I can obviously cut them myself to metric widths, so that part isn't a really bad deal.

Also, I modeled it in Sketchup in the Profiled Modulation 1 array. Tim, I figured you would be pleased if I posted it here so I will. Of course you can distribute it at will. If you'd like me to take it down for any reason let me know.

Edit: I can't wait for the B2!

I just installed Reflex on another computer and started testing it out with imperial units (depths based on 12.3 mm units, which I've read is closer to the actual thickness of 1/2" nominal lumber).

The performance changes a bit, but not for the worse (so far it looks to be slightly better performance, perhaps because the overall unit is taller)... but here's the catch: if you scale the entire diffuser up in size (increasing the well width by the same proportion of the depth unit increase), the performance is reduced. So, it looks like the well widths should remain close to 60mm.

I'll post the performance results of the imperial version of A1-LF in the near future!
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25th September 2012
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Diffusion Coefficients

Hey everyone,

Before I post the imperial version of the design, here are the coefficients for a single module of the metric version. In practice you would use more than one module (see the link in the first post for multi-module performance coefficients), but for metric-imperial comparison sake I'm starting off on a module-module basis.

Note that the modules were optimized to have a relatively flat diffusion coefficient spectra when arranged in an array of 5.







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27th September 2012
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And below are the diffusion coefficients for an array of 5 modules, mounted using a profiled modulation (this is the recommended way to mount them).

There may be other useful modulations, so if anyone has Reflex installed feel free to try out various ways of mounting the array!

E.g., if you plan to mount an array of 7 modules, a low frequency fractal modulation would be work well (7 modules would be mounted at depths proportional to the 7 wells depths of the original diffuser... creating a nested diffuser structure). This is described in more detail here: 7 module profiled modulation.

5-MODULE PROFILED MODULATION




7-MODULE PROFILED MODULATION (LOW FREQ 'FRACTAL MODULATION') - DETAILS GIVEN HERE




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28th September 2012
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Hey Tim,

Just to be sure, all the charts in the above post are metric, correct?

---------

Also, increasing the overall size to imperial shouldn't be necessary. Thinning wood to metric would be a real pain for most ordinary folk, but cutting them to any width shouldn't be any more of a hassle. Also, the height being imperial won't make a difference to their performance either.

I did try Reflex a bit but suck at the controls. I'm hoping to get better with it this week so I can try different variations of multiple modules. Perhaps a barker sequence or MLS sequence could see some cool results as well in that you could stretch to any # of modules you wish. I wish I knew more about these things (Or I wish I would just buy Acoustic Absorbers & Diffusors already!!) so it wouldn't all be trial and error - but that's the most convincing way to learn anyways, right?

Then again, I suppose I could at least read the diffusion section in the MHOA since I already have it...
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28th September 2012
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I am somewhat interested in this simple to build optimized diffuser, but unconvinced. Have you any predictions for other angles of incidence?

EDIT: I just noticed the last pictures, and they do.

But I am still wondering where the optimization is. Is it the frequency domain performance, ease of construction, or something else?
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28th September 2012
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Quote:
Originally Posted by kasmira View Post
Hey Tim,

Just to be sure, all the charts in the above post are metric, correct?

---------

Also, increasing the overall size to imperial shouldn't be necessary. Thinning wood to metric would be a real pain for most ordinary folk, but cutting them to any width shouldn't be any more of a hassle. Also, the height being imperial won't make a difference to their performance either.

I did try Reflex a bit but suck at the controls. I'm hoping to get better with it this week so I can try different variations of multiple modules. Perhaps a barker sequence or MLS sequence could see some cool results as well in that you could stretch to any # of modules you wish. I wish I knew more about these things (Or I wish I would just buy Acoustic Absorbers & Diffusors already!!) so it wouldn't all be trial and error - but that's the most convincing way to learn anyways, right?

Then again, I suppose I could at least read the diffusion section in the MHOA since I already have it...
The above images show the metric version. I've not yet posted the imperial version of the coefficients but I will soon. Basically, standard 1/2" material (actual thickness is typically 12.3 mm) is used as the step size instead of 10 mm material.

Yes, you could potentially modulate them with a MLS sequence if you had a large surface to place them on.
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28th September 2012
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Quote:
Originally Posted by OpusOfTrolls View Post
I am somewhat interested in this simple to build optimized diffuser, but unconvinced. Have you any predictions for other angles of incidence?

EDIT: I just noticed the last pictures, and they do.

But I am still wondering where the optimization is. Is it the frequency domain performance, ease of construction, or something else?
Glad you're interested in the underlying science / math .

I have predictions for 3 angles of incidence (0 degrees, -25 degrees, -45 degrees), as well as a diffuse field (random angles of incidence). More predictions are in the download area.

Details of the optimization system are given in the diffuser design thesis, which you can download here.
  • Chapter 3 outlines the design problem.
  • Chapter 5 explains the diffusion quality measurement methods.
  • Chapter 7 explains the optimization algorithm.

The Design by Optimization System
The design system is basically an efficient trial an error algorithm that uses physical modelling to test the trials, and evolutionary optimization (artificial intelligence based on natural selection) to minimize the error (i.e., converge on a solution).

The process used an integer genetic algorithm to find candidate designs (trial) and evaluated the performance of candidates using a finite difference time domain (FDTD) scattering simulation. The performance of each candidate design was evaluated using a diffusion coefficient based on the "standard error", which is an important quantity used in statistics (see Chapter 5 to see how the diffusion coefficient was calculated). The objective was to minimize the difference between the diffusion coefficient and "ideal diffusion". I.e., minimize the error.

New designs were generated and tested by the system, and using trial and error feedback the system converged to a design that meets the design objectives given below (see Chapter 7 of the thesis for visuals of the convergence process).


Design Objectives
These were the optimization objectives:

The successful diffuser design had to satisfy the following criteria:

  1. It must be shallower than existing profiled diffusers, with comparable or better broadband diffusion performance.
  2. It should be modular, and designed to disperse sound optimally when modules are arranged an array.
  3. It must be economical to manufacture.
  4. The geometry must not pose obvious hazards to human safety.
  5. The design method should utilize high quality scattering predictions, but it should not require a custom boundary element implementation (Finite difference time domain was used instead).
  6. Optimization must produce a suitable design within a reasonable solution time.
  7. The design should be suited for application on the back wall of a small-to-medium sized recording studio control room, where the purpose is to disperse first reflections from a hypothetical sound wave arriving at zero degrees incidence.
  8. The design method should also be applicable to solving a larger problem: optimizing a surface for uniform scattering of an incident wave from any direction.

The designs you see were optimized for an incident sound wave at zero degrees, but they've also been tested at other incident angles. They performed quite well at all angles tested.

Optimization Frequencies
A Quote from section 7.2 of my thesis, "The Lean Optimization of Acoustic Diffusers":

"Optimization was performed across a range of frequencies that roughly span the 10dB-bandwidth of the excitation pulse. This will be called the diffusion band. 12 discrete frequencies were chosen for optimization, distributed quasi-randomly in the diffusion band. The response spectrum was characterized by a 4096 point FFT (fast fourier transform), and the optimization frequencies were the FFT bins centered on {102, 250, 449, 574, 700, 824, 949, 1102, 1250, 1450, 1700 and 1950 Hz}. This sparse set of FFT bins was chosen in an effort to clearly define the optimization objective, aid in visualizing progress and speed up convergence.

When the goal is to optimize for twelve specific frequencies (rather than all frequencies), the disparity between good solutions and average solutions is higher and results can be compared more meaningfully. Moreover, Cox found that optimization at seven frequencies [11] was sufficient to achieve good dispersion over the entire bandwidth."

To emphasize the importance of the lower-mid frequencies, the range 400-1250 Hz received the highest density of optimization frequencies. Another option is to optimize across all FFT bins in the diffusion band, assigning relative weights to each bin when solving Eq. (5.2).



Does this answer your questions? I realize I just unleashed a bunch of technical jargon so please let me know if anything is not clear!
#27
29th September 2012
Old 29th September 2012
  #27
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Location: Netherlands
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Thanks Tim for giving this
Today I made a metric diffuser for testing and practising. Found some slats with good dimensions what gives a minimum on sawing.
Basis was a slat of 56mm( 7 x 8mm) and 12 mm height. In the DIY store they saw a MDF bottom 61cm by 38cm(7 x 56mm) and another MDF plate 61 by 28cm( 5 x 56mm) for free.
For the fractals I found a slat 25mm(5 x 5) by 40mm( 5x8mm), so very practical.
The 'difficult' part was to mill manual the 3 and 4 units height in the fractal slat. Need some more practising to get a good result but the photos shows the 'protoype'.

The sound diffuser works great especially when you put the fractals on it.
Attached Thumbnails
DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-diy-blueprint-arqen1.jpg   DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-diy-blueprint-arqen2.jpg  
#28
29th September 2012
Old 29th September 2012
  #28
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Quote:
Originally Posted by Arqen View Post
Does this answer your questions? I realize I just unleashed a bunch of technical jargon so please let me know if anything is not clear!
I guess so. I would like to hear one!
Arqen
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#29
30th September 2012
Old 30th September 2012
  #29
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Thread Starter
Quote:
Originally Posted by Schaap View Post
Thanks Tim for giving this
Today I made a metric diffuser for testing and practising. Found some slats with good dimensions what gives a minimum on sawing.
Basis was a slat of 56mm( 7 x 8mm) and 12 mm height. In the DIY store they saw a MDF bottom 61cm by 38cm(7 x 56mm) and another MDF plate 61 by 28cm( 5 x 56mm) for free.
For the fractals I found a slat 25mm(5 x 5) by 40mm( 5x8mm), so very practical.
The 'difficult' part was to mill manual the 3 and 4 units height in the fractal slat. Need some more practising to get a good result but the photos shows the 'protoype'.

The sound diffuser works great especially when you put the fractals on it.
Wow! I'm surprised you actually went ahead to make a fractal diffuser!

Congrats! As far as I know, you're the first person to make a fractal version of one of the diffusers.

If you make multiple of these, I recommend you mount them using the "profiled modulation" given on the last page of the blueprints for stepped diffuser A1-LF (to reduce the effects of periodicity in the array).

I.e., mount modules with varying depths as follows: [0 cm, 5 cm, 6 cm, 5 cm, 0 cm]

You could also mount 7 modules using a low frequency fractal modulation. So you'd have a 3rd order nested fractal! For example, you could mount 7 modules at these depths:

[0cm, 8 cm, 10 cm, 6 cm, 10 cm, 8 cm, 0 cm]

I've attached images and diffusion coefficients for each of these modulations (as applied to the basic stepped diffuser).
Attached Images

Last edited by Arqen; 30th September 2012 at 08:20 PM.. Reason: Changed mm dimension to cm
#30
30th September 2012
Old 30th September 2012
  #30
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Joined: Sep 2004
Location: Netherlands
Posts: 530

Quote:
Originally Posted by Arqen View Post
Wow! I'm surprised you actually went ahead to make a fractal diffuser!

Congrats! As far as I know, you're the first person to make a fractal version of one of the diffusers.

If you make multiple of these, I recommend you mount them using the "profiled modulation" given on the last page of the blueprints for stepped diffuser A1-LF (to reduce the effects of periodicity in the array).

I.e., mount modules with varying depths as follows: [0 cm, 5 cm, 6 cm, 5 cm, 0 cm]
That's my goal when I have the time to build them. The great thing is they can be build fast without the 'religious labour' of e.g. a 13x12 skyline diffuser.

Should the varying depths of the modules not be 0,5,6,4,6,5,0 cm?
As said they work very well so thanks again!

The 80, 100cm variant is rather mega and I think you need a large room for that.
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