Arqen
#31
30th September 2012
30th September 2012
#31

Quote:
Originally Posted by Schaap
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.
Oops! I meant 100 mm, not 100 cm. Thanks for noticing that. And I'm VERY pleased to hear that these were easier to build than the skyline diffusers (For the record, I think the Skyline rocks... and I expect for certain people, building one might be a labour of love).

The "fractal" modulation [0, 8 , 10, 6, 10, 8, 0] cm is based on the depth sequence of the stepped diffuser [0, 4, 5, 3, 5, 4, 0] multiplied by 2. Why? Because it was a simple modulation to try without making the diffuser too deep, and it performed well when tested in Reflex.

There are many possible modulations, and [0, 5, 6, 4, 6, 5, 0] cm might also work.

These profiled modulations were found through experimentation. I could supercharge the process using the design by optimization system, which I used to create the base shapes... but that would take time to set up, run and verify...

If you did not mind a thick diffuser, you could create a low frequency fractal stage (a profiled modulation) with the proportions equal to the stepped diffuser (i.e., keeping the width:depth ratio consistent, where width:depth ratio = 42 cm/5cm = 8.4). Considering an array of 7 diffuser modules (294 cm wide), the deepest step of the profiles modulation would be 294 / 8.4 = 35. Since the deepest step of the stepped diffuser is 5cm, you would scale all the depths by 35 cm / 5 cm = 7.

This would give you a profiled modulation of 7x[stepped diffuser depths] = [0, 28, 35, 21, 35, 28, 0] cm... resulting in a much deeper diffuser than the one we started with!
Arqen
#32
2nd October 2012
2nd October 2012
#32

Quote:
Originally Posted by OpusOfTrolls
But I am still wondering where the optimization is. Is it the frequency domain performance, ease of construction, or something else?
Let me be more specific about that...

The optimization is in the spatial dispersion performance (since this was designed as a 1D diffuser, the spatial dispersion performance is the efficacy by which sound energy is scattered uniformly in a 2D plane).

While optimizing, I placed a constraint on the maximum depth of the diffuser, and a constraint on the maximum size of the diffuser. Basically, I forced the diffuser to be less than 10 cm deep, and consist of five modules, with each module having having 7 wells (i.e., 7 "steps").

The 5 modules were placed in an array according to the aperiodic modulation {1 0 1 1 0}. Then, with all the geometric constraints in place, I ran my optimization code. The goal of the optimization was to intelligently navigate through millions of candidate designs and find shapes that produce excellent spatial diffusion, while retaining a compact, modular form factor. Even though the maximum allowed depth was 10cm, one of the top performing shapes (A1-LF) was surprisingly shallow, having an operational depth of just 5cm!

Is this more clear than my original explanation?

#33
3rd October 2012
3rd October 2012
#33
Lives for gear

10mm wood of ANY sort is not a standard size in Australia and impossible to find.

What can I do?

Plenty of 9mm, but I presume this will throw off the predicted performance. Any one else having this problem?

I wonder if it would be ok to make them out of 10mm drywall? Got some of that left over from the studio build. Not as attractive as wood, but a coat of primer and paint and they should look ok, as long as they function ok with that material...
Arqen
#34
3rd October 2012
3rd October 2012
#34

Quote:
10mm wood of ANY sort is not a standard size in Australia and impossible to find.

What can I do?

Plenty of 9mm, but I presume this will throw off the predicted performance. Any one else having this problem?

I wonder if it would be ok to make them out of 10mm drywall? Got some of that left over from the studio build. Not as attractive as wood, but a coat of primer and paint and they should look ok, as long as they function ok with that material...
Using AFMG Reflex, I tested out a version based on imperial units (depths based on 12.3 mm units, which I've read is closer to the actual thickness of 1/2" nominal lumber). I.e., 1/2" standard material (typically 12.3 mm actual thickness) is used as the step size instead of 10 mm material.

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 depths should remain close to 60mm.

Yes, you could also make them out of 10mm drywall if you want. But given the choice, I recommend 12.3 mm material over 9 mm material (partly because I've not tested the results with 9 mm material).

Also, consider that 1x3" softwood lumber has an actual size of 19 mm x 64 mm. While I've not looked into how it would fit together, you might be able to fabricate a diffuser using this 19 mm x 64 mm material as building blocks.
#35
3rd October 2012
3rd October 2012
#35
Gear maniac

Thanks tim, that's good news. Question...

How much taller? And do they absolutely have to be made taller to maintain satisfactory performance? 12mm stock should make things a bit easier for me.
Arqen
#36
4th October 2012
4th October 2012
#36

Quote:
Thanks tim, that's good news. Question...

How much taller? And do they absolutely have to be made taller to maintain satisfactory performance? 12mm stock should make things a bit easier for me.
If we assume the base of the diffuser is the same depth for both the imperial and metric version, the imperial version would only be 11.5 mm taller. If the base is also made of thicker material (12.3 mm vs 10 mm), the imperial version would be 13.8 mm taller (or rather, deeper I should say). So, not a noticeable difference from an aesthetic standpoint.

If you're using 12.3 mm material for the steps and the base, the full depth of the diffuser (including the base / mount board) would be 73.8 mm.
#37
4th October 2012
4th October 2012
#37
Gear maniac

Ok so based on 12mm material we are looking at a height of 131.5mm tall correct?
#38
4th October 2012
4th October 2012
#38
Lives for gear

Quote:
Originally Posted by Arqen
Using AFMG Reflex...
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...
Thanks again Tim. Would you mind posting the graph so that we can see the performance difference?

[Quote]So, it looks like the well depths should remain close to 60mm.[quote/]
Sorry, did you mean to say, "should remain close to 50..."? Or are you including the base/mounting?
#39
4th October 2012
4th October 2012
#39
Gear maniac

Ok so based on 12mm material we are looking at a height of 131.5mm tall correct?

Or maybe when you say taller, tu mean deeper? From back to front? And they are still 1200mm tall? Sorry for the confusion...
Arqen
#40
4th October 2012
4th October 2012
#40

Diffusion Coefficients & Scattering Coefficients

Quote:
Originally Posted by John White
Thanks again Tim. Would you mind posting the graph so that we can see the performance difference?

Quote: "So, it looks like the well depths should remain close to 60mm."
Sorry, did you mean to say, "should remain close to 50..."? Or are you including the base/mounting?
Hi Jon,

I've posted the diffusion coefficient plots for the imperial version below of stepped diffuser A1-LF below.

Also, I meant to say "the well widths should remain close to 60 mm". Sorry for the confusion.

As you can see from the coefficient plots below, 5 modules of the metric version have a smoother diffusion coefficient spectra than the imperial version for an incident wave at zero degrees. This makes sense, because this is the configuration I used to optimize the diffuser array. However, the imperial version has a higher average diffusion coefficient under most other conditions I've tested.

A big performance boost can be gained by mounting the modules at different depths (what I call a "profiled modulation"). In the near future, I'll post an example of a profiled modulation applied to the imperial diffuser array.

Here is the performance at 0 degrees incidence for 1 module of the imperial version

Here are the diffusion coefficients for 5 modules of the imperial version (with no modulation):

Diffusion performance at 0 degrees incidence for 1 module of the metric version

Diffusion coefficients for 5 modules of the metric version (with no modulation):

Arqen
#41
4th October 2012
4th October 2012
#41

Quote:
Ok so based on 12mm material we are looking at a height of 131.5mm tall correct?

Or maybe when you say taller, tu mean deeper? From back to front? And they are still 1200mm tall? Sorry for the confusion...
No problem! I caused the confusion by sometimes using the words "depth and height" interchangeably. From now on, depth will refer to how far the diffuser sticks out of the wall. Height (which is 1200 mm) will refer to how tall the diffuser is when mounted on a wall (i.e., how long it is when lying on a flat surface).

Using 12.3 mm material for everything (including the base), the total depth is:

Total Depth of Imperial Diffuser = Base Depth + Operational Depth = (12.3 mm + 5*12.3 mm) = 73.8 mm

Where the operational depth (5*12.3 mm) is simply the depth of the deepest "step" (I.e., the depth of the deepest well).
Arqen
#42
5th October 2012
5th October 2012
#42

Fractal Sound Diffuser DIY Design Specs

Hi guys,

Some of you were interested in building the fractal sound diffuser B2-Frac. Well, I've now posted the specs.

Because there are many different ways one can fabricate B2-Frac, I've simply uploaded a document that lists the geometric details (instead of detailed fabrication drawings), including the depth of each well .

I've not given much thought into a fabrication strategy for this complex diffuser form, so I want to see what we can come up with together. How would you build this diffuser? Let the ideas flow!
#43
5th October 2012
5th October 2012
#43
Lives for gear

That's great Tim. I know it's a lot of work. I'll try to make sense of the graphs this weekend.
Arqen
#44
6th October 2012
6th October 2012
#44

Quote:
Originally Posted by John White
That's great Tim. I know it's a lot of work. I'll try to make sense of the graphs this weekend.
No problem, John. I'm happy to make the diffuser designs and performance results available... everyone benefits from this stuff.
#45
7th October 2012
7th October 2012
#45
Gear maniac

Whoa!! Now I have to make my stepped diffusers diffractals , has to be done. I am only just starting to build them so it's now or never. I'm racking
My brain as to best way to fabricate it, haven't come up with anything yet but I'm still trying.

Tim it's awesome what your doing here. And I'm sure for many like myself very timely as we are at the stage of treating new rooms. So a big thanks to you and I hope this thread has a long life. Should prove very educational.
Arqen
#46
7th October 2012
7th October 2012
#46

Quote:
Whoa!! Now I have to make my stepped diffusers diffractals , has to be done. I am only just starting to build them so it's now or never. I'm racking
My brain as to best way to fabricate it, haven't come up with anything yet but I'm still trying.

Tim it's awesome what your doing here. And I'm sure for many like myself very timely as we are at the stage of treating new rooms. So a big thanks to you and I hope this thread has a long life. Should prove very educational.

I've not yet come up with a great way to turn these into fractals, but if we can come up with an easily repeatable process that would be great.

Schaap managed to make a fractal version of A1-LF, but it looks like it took a lot a work!
#47
8th October 2012
8th October 2012
#47
Gear maniac

Schapp? Step on up mate. How'd ya do it?
Arqen
#48
9th October 2012
9th October 2012
#48

Here's how Schaap made the fractal version of A1-LF:

Quote:
Originally Posted by Schaap
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.
#49
10th October 2012
10th October 2012
#49
Lives for gear

Quote:
Schapp? Step on up mate. How'd ya do it?
The trick is I think to find the right sizes in the DIY store. The easiest size is the one with a width you can divide by 7, because 0,4,5,3,5,4,0 is a sequence of 7 . That's why I choose 56mm( 7 x 8 mm)
Regarding the height almost all slats near 1cm are 12 mm( 1/2 inch). So the base is for the module is a 12x56 slat. Another advantage is that for milling the fractals a standard 'millknife' is 8 mm.

One standard height is 12 mm and to make the module the 3 is the sequence was made with a 27mm slat and on top a 8mm MDF 'plateau'. That gives 35mm, but let's say 36mm(3 x 12mm). On the 'plateau' you can lay one and the two 12x56mm slats to give the 4 and 5 of the sequence. See the pictures. You can use 12mm MDF what is cheaper but for 'esthetics' I choose wood.

The fractals are about 25mm high (is the 5 in the sequnce) . Just mill 5mm on both sides and in the middle 1 cm. The width is about 40mm and that's become the 4,5,3,5,4. Put it in the middle of the 56mm slat and you have a 0,4,5,3,5,4,0 fractal
Attached Thumbnails

#50
10th October 2012
10th October 2012
#50
Gear maniac

Thanks schnapps that's great info.

Tim,

In the your plans you show a graphic in green of the array of 5 panels, demonstrating mounting with modulation. Each of the modules on the end, that is the ones at 0, have a gap to the panel next to it. Is this just the picture or should there be an actual gap at each end. I am on hold till I can confirm this. I'm planning to have no gap and have each panel mounted next to each other side by side, with modulation of course.

Secondly modulation should work from 0 and go foward 5cm then foward 6cm then work back down to zero shouldn't it? I originally had it going backwards 5cm then 6cm etc. I think this may be wrong and just caught this in time?? Thanks.
Arqen
#51
10th October 2012
10th October 2012
#51

Quote:
Thanks schnapps that's great info.

Tim,

In the your plans you show a graphic in green of the array of 5 panels, demonstrating mounting with modulation. Each of the modules on the end, that is the ones at 0, have a gap to the panel next to it. Is this just the picture or should there be an actual gap at each end. I am on hold till I can confirm this. I'm planning to have no gap and have each panel mounted next to each other side by side, with modulation of course.

Secondly modulation should work from 0 and go foward 5cm then foward 6cm then work back down to zero shouldn't it? I originally had it going backwards 5cm then 6cm etc. I think this may be wrong and just caught this in time?? Thanks.
Yes, the gaps should be there... but they are not actually gaps.

Each module is composed of 7 steps, with depths based on the sequence {0, 40, 50, 30, 50, 40, 0} mm.
So that gap is actually a diffuser step with a 0mm depth.

To help make it more clear, note that in the green graphic the base of the diffuser is not shown as a thin grey line (it's not green). So, what looks like a gap is actually the shallowest step of the diffuser, which has a depth of 0mm above the base.

You're right about the way the modulation works. The outer 2 modules (we'll call them modules 1 and 5) are mounted directly onto the wall. The next 2 modules in from them (modules 2 and 4) stick out of the wall 5 cm. And the middle module sticks out of the wall 6cm.

Here's a crude attempt at illustrating the 5 levels.

top dotted line is middle module ______----------______
''''''`````````````````` ______|___________________|______ the bottom line of this image represents the wall.

I can see how it might be confusing, depending on how you view the image in the document!
#52
10th October 2012
10th October 2012
#52
Lives for gear

Quote:
Originally Posted by Arqen
You're right about the way the modulation works. The outer 2 modules (we'll call them modules 1 and 5) are mounted directly onto the wall. The next 2 modules in from them (modules 2 and 4) stick out of the wall 5 cm. And the middle module sticks out of the wall 6cm.
Hey Tim,

Today I 'compared' the fractals(1") - flat - with QRD's of 1" , so called 'Flutterfree" and by hearing I couldn't experienced much difference.
When the fractals were modulated by 1,2,0,2,1 it took the diffusion to a higher level and so very noticeable difference.
In the meantime I've finished the fourth module

Henk
#53
10th October 2012
10th October 2012
#53
Lives for gear

Quote:
Thanks schnapps
Ja Bitte, viel schnapps!!
Arqen
#54
10th October 2012
10th October 2012
#54

Quote:
Originally Posted by Schaap
Hey Tim,

Today I 'compared' the fractals(1") - flat - with QRD's of 1" , so called 'Flutterfree" and by hearing I couldn't experienced much difference.
When the fractals were modulated by 1,2,0,2,1 it took the diffusion to a higher level and so very noticeable difference.
In the meantime I've finished the fourth module

Henk
Awesome, Henk!

Thanks for being so proactive by building these, trying them out and keeping us all informed!

I'm glad the modulation 1,2,0,2,1 gives a noticeably improved performance. Sounds like a good way to mount the diffuser array while keeping it low profile.

Tim
#55
11th October 2012
11th October 2012
#55
Gear maniac

Schapp,

I'm curious if you tried the stepped diffuser before you fractalised it? How did it sound compared to a flat wall, noticeable difference? I'm thinking of its limited bandwidth of only 800hz-3000hz or so and it's overall effectiveness. Thanks
#56
11th October 2012
11th October 2012
#56
Lives for gear

Quote:
Schapp,

I'm curious if you tried the stepped diffuser before you fractalised it? How did it sound compared to a flat wall, noticeable difference? I'm thinking of its limited bandwidth of only 800hz-3000hz or so and it's overall effectiveness. Thanks
Hi,

Yes, it works noticeable. The fractals are really the 'icing on the cake'. The effectiveness increases with the modulation, so different heigts pro module according to Tim's sequence definitely improves the diffusion at a very noticeable level.
#57
11th October 2012
11th October 2012
#57
Lives for gear

Quote:
Originally Posted by Arqen
Using AFMG Reflex, I tested out a version based on imperial units (depths based on 12.3 mm units, which I've read is closer to the actual thickness of 1/2" nominal lumber). I.e., 1/2" standard material (typically 12.3 mm actual thickness) is used as the step size instead of 10 mm material.
Where did you get the number 12.3 mm? Not to destroy all the work you've done, but that isn't the actual size for any lumber I've seen. Typically, 1/2" lumber nominal is 3/8" actual (9.525mm)

Also, if we were using something like MDF, plywood, hardwood plywood, etc - the actual thickness is the nominal thickness (at least, from what I've seen). Only with boards (1x3, 2x4 etc) is it not. So we could calculate it with either .75" (19.05mm) - the actual thickness of a 1x# board, or by exact measurements using MDF or something of the sort.

Also, found this on Home Depot online: 5.0 mm x 2 ft. x 4 ft. Lauan Moisture Resistant Underlayment Handy Panel-1507004 at The Home Depot

Only thing I can really find that looks useful that is actually in metric units..

Damn the imperial system
#58
11th October 2012
11th October 2012
#58
Lives for gear

Kasimira,

If your in the metric bit of the world as I, why not just use 12mm stuff? Thats what Im doing, Im sure its close enough to the 12.3mm thickness Tim simulated to not make any performance difference.

I just noticed your in the US so not a metric country.Isnt 1/2 inch 12.7mm anyway? Close enough?
#59
11th October 2012
11th October 2012
#59
Lives for gear

Quote:
Kasimira,

If your in the metric bit of the world as I, why not just use 12mm stuff? Thats what Im doing, Im sure its close enough to the 12.3mm thickness Tim simulated to not make any performance difference.
Tim's original design is using 10mm (1cm) thickness wood (not 12.3mm). So if I was somewhere that used metric sizes...I would just go with his original design. 12.3mm was his estimation for the actual thickness of 1/2" imperial lumber (which I don't believe is the case)

I'm not on the metric side of the world...only wish I was (I do measure & estimate things in cm and meters though)
#60
11th October 2012
11th October 2012
#60
Lives for gear

10mm thats right, sorry. I also went back and edited my post before I saw your reply so sorry bout that as well.

Im not sure what it is exactly you cant find. surely 3/8ths would be the go? Or something closer to 12mm. Even a small increase in performance with something around 12mm too apparently.

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