Even if painted, EPS will still have much more absorption than wood. If the numbers are correct on your non-painted vs painted absorption measurements (has anyone replicated this?), painted EPS has about 3-5x the absoprtion I'd expect from wood. Granted, it's not a lot of absorption in either case.

If wells are deep enough to handle low frequencies, wood will provide much greater diffusion/scattering in the low end - whereas EPS will provide little to none.

Sorry, but you are incorrect.

EPS is a stiff material (again, assuming not too low density EPS as stated in the post linked to above). Assuming mounted firmly (glued) to a rigid surface that cannot vibrate easily, and assuming painted so the pours in the surface of EPS are sealed; a diffuser made of EPS will behave more or less identical to a wooden diffuser (and naturally assuming the exact same shape) since it will not vibrate either (unless if used as the lid of a membrane absorber as discussed below).

It´s an unfortunate misconception that an EPS diffuser (just because it´s light weight I assume) will not reflect as a wooden diffuser would. As mentioned in my link above; the light weight of an EPS diffuser can be used to our advantage since it´s possible to construct a surface that combines diffusion and membrane absorption for the modal range. This is not possible with wooden diffusers since they are often way too heavy to be used as the mass of the panel of a membrane absorber.

Not about diffusers and EPS, but the general discussion covers the same basic principles:
Flooring question

Anyone have any thoughts on my question above? Thanks

Jens,

What am I wrong about? Using your own data you've pointed to, painted EPS clearly absorbs far more than wood - about 5x as much absorption on average.

This even assumes your painted vs non-painted graph is accurate (which you haven't backed up with any independent data - though it seems reasonable).

Are you also trying to say painted EPS will diffuse low frequencies as effectively as wood (assuming wells are deep enough)?

Specify what I'm wrong about please. You apparently sell these things, so the burden is on you to make a good argument. You should be able to do so in a simple and clear way too - not by misdirecting with confusing technical jargon.


Attachment:
Wood floor absorption coefficient on the left, Jen's painted vs non-painted EPS graph on the right.

You are assuming that other diffusers (not even the same shape …) made out of wood absorbs less than diffusers made out of EPS. This is often simply not true.

Perhaps you don´t know that every diffuser (assuming good diffusion performance) will also absorb some sound. This is inevitable. If you study the science of diffusers (the book “Acoustic Absorbers and Diffusers is a very good start), you will soon realize this fact. How much it absorbs depends largely on construction details and naturally the shape of it. The material (assuming stiff and not too rough and/or porous) does not matter much at all. To state that wooden diffusers absorb less than EPS diffusers is just ignorant.

Wood and EPS (again, assuming painted/coated, glued to a solid surface and not too low density EPS) will reflect an incoming sound wave very similarly since the surface is not free to move, so no; there is no difference between wood and EPS in this case. Again, lightweight diffusers (not only EPS) can be used as part of a membrane design to absorb very low frequencies but this is obviously not a negative but a good thing.

Do you think that one of the most respected manufacturer of diffusers (RPG … oh, and guess who is the chairman of that company … one of the writers of the book mentioned above) would use EPS if what you are (incorrectly) suggesting was true?

Unless you are ready to back up you claims with some comparative data (that means comparing apples to apples, you cannot compare two completely different diffusers that are possibly also measured using different measuring setups and techniques), I suggest that you stop making false claims, fueling modern myths.

Did you check the flooring thread?

It´s like saying that a solid concrete floor will reflect mids and highs better than a thin wood tile floor on leveling polyethylene. That’s simply not true. If you check that tread, you´ll see that the only difference is at the resonant frequency for the new floor as it behaves like a membrane absorber. The frequency range above is not affected. If the floor was glued to the concrete slab, the result would have been the same as only concrete since the floor would not be free to vibrate (all acousticians participating in that thread agrees on this), exactly the same as an EPS diffuser glued to an immovable surface; it would reflect low frequencies as well as the bare wall (with the exception of absorption caused by the shape of the diffuser of course, but that would be the same for a wooden diffuser assuming the same shape).

Flooring question

You're the one who should be providing the comparative data since you're the one making the claim your painted EPS optifuser is as effective as wood. A simple (independent) absorption test on painted EPS vs an identical shaped piece of wood might settle it. If it's true, I'll buy some.


I'm saying, "Where's the data on this?" Straightforward absorption test data, not vernacular only a PHd in acoustic engineering could refute.

This is a straw man. Of course I know wood always absorbs some amount of sound (look at the attachment in my last post).

To state EPS diffusers absorb the same as wooden diffusers is a claim that needs to be proven.


This industry is filled with contradictory/misleading information and there seems to be absolutely no one keeping it in check. It's as if there's an unspoken agreement between acoustic designers on this forum not to call each other out for fear of themselves being ousted as peddling psuedo-scientific products/methods.

By the way, the "optimized" DIY diffuser, the topic of this thread and Arqen's thesis, relies almost entirely on the AFMG software being accurate. 5 minutes of fiddling with designs inside that software should raise eyebrows of even the most naive people.

Since you are the one making a controversial claim, the burden of proof is on you.

Again, a piece of high density painted EPS glued to a solid surface will reflect more or less exactly like a piece of wood of the same shape.

Oh, and regarding AFMG Reflex; any tool used incorrectly will give you incorrect predictions. The use of BEM to simulate diffuser performance is well tested and confirmed (as can be read I the book I recommended in previous post. Do read it, it's very informative).

That's not what I'm saying, perhaps this is the issue. ANY diffuser will absorb sound, be it made of marble or steel, doesent matter. It's the shape that causes losses and results in absorption.

And since EPS is a stiff material, it will also reflect like any other solid material (again assuming the stuff I don't want to repeat again).

Which setup do you think would reflect 125 Hz the most;


12 mm plywood over 50 mm airgap

or

12 mm of EPS over 45 mm airgap?

Considering alpha 0.5 is 3 dB of attenuation, what are the actual values you are describing here? What is the difference between alpha 0.2 and 0.3? Sorry if I'm misunderstanding something

Acoustic Absorbers and Diffusers, Third Edition: Theory, Design and Application - Trevor Cox, Peter D’Antonio - Google Bocker

This book is considered by many to be the bible when it comes to diffusers, and EPS is mentioned only once (in fairly close proximity of the term absorption) and if there was any downside in this regard with using EPS, it would surely be mentioned here. Instead, the importance of tight seals are brought up ... so ...

The weight is not too bad at all, maybe 70 lbs max? I used cedar for everything and I used the thin cedar fencing for the main slats which are about 1/4 " thick by 5 1/2" wide and 6' lenght. I then used 1 1/2" thick cedar decking which I cut into 1" strips for spacing. I used 8" cedar planks for the sides and top/Bottom of frame. Supplies were bought from Lowes and some other Bits at Home depot. My version is not quite accurate as to the design but it sounds great in the room as it adds the air that I wanted to hear. My version cuts down on quite a bit of weight as well.

Going bidirectional?

Hello Tim
First of all - Your work has had a major impact on how I now envision my music room (2-channel).
I am extremely grateful! Your support of the community is commendable.
It's now my turn to pick your brain...

My acoustics engineer spec'd the use of Skyline diffusers. I was planning to make them myself as I have all the equipment.
Then I stumbled upon your design - LeanFuser.
The main drawback he sees with it is the fact that the diffusion is only on one axis.
What if I build 4 single panels (420mm x 420m) and I put the 4 vertically, varying the orientation?

This would replace a Skyline surface of 2 x 5 feet.
In the image, yellow are diffusers, blue absorbers.

Thank you very much!

Hey all,

First, a big thank you for the blueprint!

I just received the leanfractal email... The one about the fractal cell build... I was wondering what are the inches equivalent? I will use ½inches plywood to build the leanfractal... I know we have to stick to 60mm well, but have to double the 10mm for depth (10mm is ½ (or 12mm)).

But I am not sure about the small cell dimension, depth, wide, height.
Thesis says : 11, 14, 9, 14, 11 mm. Since it's mm, really hard to convert it to inches because of the small mm difference.. I'm puzzled.. Or I should just slice them using mm dimension but that would be a amazing amount of work if I don't mill them... Thanks for any help on this one! I added an inches version for the current panel.

I attached the picture included in the email and another picture of diffusers I built with different type of wood.

And here is the FAQ.


"In the thesis I used a fractal step increment of 2.85mm for the fractal cells (see Tables 5 and 6 on page 51 of the thesis). Anything smaller than this would have taken too long to simulate, and would have left a performance gap in the diffusion spectrum. The resulting depth sequence for the small fractal cells is [0, 11.4, 14.25, 8.55, 14.25, 11.4 0] mm. To make milling easier you can round the sequence to [0, 11, 14, 9, 14, 11 0] mm.

If you prefer a spikier look you can increase the depth of the fractal cells. For example, if the depth of the fractal cells are doubled they would be about [0, 22, 28, 17, 28, 22, 0] mm deep. Or you can simply use [0, 20, 25, 15, 25, 20, 0] mm, which are the fractal dimensions that Schaap demonstrates here. Increasing the fractal cell depth is likely to increase the high frequency performance, but if you take this to the extreme these deeper fractal cells may be fragile."

Think it should do this way...

Easiest way to make groove for the fractal is to use a dado set... Can't get it wrong and really fast... Took me around 1h30 to make 210 grooves. (70 pieces x 3 cuts)

Have to assemble now :D

I’ll join the parade. I made the three panel lean diffusor and noticed an improvement in the clarity of vocals in my living/ listening room. Initially, I prototyped the model 4 in MDF with a 70 mm center panel stand-off but ended up with the flat version. It is only 13” high and made out of walnut, mostly from cut offs I had laying around from a previous project. I call this the high WAF version. See photo. I have lots of constraints in my mixed use room. So, a diffusor doubling as wall art is a win/ win situation. I’m sure a taller version would be better sound-wise but I’ll take any improvement I can get.


The “Master Handbook of Acoustics” recommends absorption at the first reflection point and Floyd Toole recommends nothing on the wall at the FRP. Recommendations also vary depending on whether it’s a studio control room or a listening space. The diffusor is 8’ away from my listening position. I don’t know if the lean diffusor is actually diffusing or just attenuating. What is noticeable when playing Pink Martini is how much clearer China Forbes’ voice is.

Thanks Tim Perry.

WAF? Wife Authorization Factor?

As for absorption at the FRP... I tend to refute that... I had absorption at FRP and as soon as I removed it.. WOW! Sound stage way larger, deeper and the details... LOL!! I built two 5 moduled fractal panels to install instead of absorption and there is no way I am going back!

To be honest, I had absorption at the beginning... Easy done.. Order, pay, delivery and you install them... You remove the echo, you are happy, you think it sounds very nice because now, no more echo, everything is tight but well.. It's like mud! Once you taste what a diffuser can do instead of absorption... You know what they say... Once you go diffusers you never go back

I now have diffusers all over my listening room and can't put enough words to describe how much the sound is better than with absorption! Yes, I still have few places with absorption but like 80-85% diffusers

YES, it is time consuming, maybe you will need to practice few ones before getting it done like a champ but remember, YOU will be AMAZED. You can upgrade your listening experience for so much less money vs spending on a XLR cable or AC power and so on...

Can you post some photos of your room? Do you have measurements before and after diffusers?

I don't have anything to make measurements and to be honest, it is something you experience, somes prefer a muddy sound, which they consider warm.. cough cough and other prefer a more analytic and realistic sound. :P)

As for the picture, it is pitch black in there, kinda hard to take pictures...

Im wondering if you could 3D print these with a 3d router (one that cuts wood).... Anyone know if theres any Solidworks designs around for these ?

Indeed it could.. .Like a CNC machine?

@ Arqen , Would a routed profile something like this triple bead and flute bit be a good approximation for a fractal implementation ?

3/16" deep and 1 3/8" wide.

Also, how much coverage is required to be useful ?

TIA

Anyone in LA built these / have recs on where to source materials? I don’t have the equipment to accurately mill myself and most of the lumber yards that offer milling services won’t guarantee accurate cuts...

I haven't built these but the last time I was at Anderson Plywood in West LA I asked about cutting and their tolerances were pretty good. You can also get some ideas just reading through this thread, remember one person found appropriate already dimensioned poplar which gets you have way there.

Thanks! Anderson was actually the first place I checked, but their website has a bunch of disclaimers re: rough cut milling only / no finished quality, and I'm not sure that warrants the additional cost over a start to finish DIY effort -- I've got a circular saw and router, may just have to bite the bullet and make a trip to the hardware store to figure things out.

I had asked the guy actually doing the cutting and he said they keep their blade sharp and could do 1/16" iirc.

But a lot would depend on who actual does the cutting that day. I've even gotten good results at the big hardware stores some of the time. But I think the stores in general don't want to guarantee things.

You should organize a "build party" in your area and pool your resources.