Making easy DIY "Depot" sound Diffuser panels, step by step

Hi bwaslo,

I built the basic design version using 60mm wide elements (7 x 60 = 420mm/ module)and the full 7 module unit - nearly 3 metres wide by 1.2M high using 9 and 12mm ply - couldn't position it at the back of the room but played with different positions with surprising effects - behind the speakers across the 'front' wall, it nearly made the sound 'mono' with very pronounced depth, even listening over 30* outside one side (of speaker) which isn't something you'd normally do, I know, but it shows how effective diffusion can be.

Anyway, I looked at the 5 module design for the first reflection points but need them to be mobile (window areas) so thinking of cutting styrene foam sheets to reduce weight and instead of gluing thin 3mm ply to the flat surfaces, thought about using venetian blind slats as they're already fully finished surfaces, but are only 50mm wide [50mm wide x 3mm thick x 'whatever' high]

I played around with Tim's program during the intro month period but didn't get the 'hang of it' unfortunately, and wondered if you still have access to it to see what depth changes are required for the 50mm wide pieces instead of the 60mm wide, and for 3 or 5 modules instead of the full 7.
 
....with surprising effects - behind the speakers across the 'front' wall, it nearly made the sound 'mono' with very pronounced depth, even listening over 30* outside one side (of speaker) which isn't something you'd normally do, I know, but it shows how effective diffusion can be.

yeah, diffusion can be pretty amazing, can't it? I think the higher usual cost and the fact that building them seems more complicated than just tossing out some kind of absorbent blob is why you don't often see them in listening rooms. But diffusers arendefinitely different animals.

Anyway, I looked at the 5 module design for the first reflection points but need them to be mobile (window areas) so thinking of cutting styrene foam sheets to reduce weight and instead of gluing thin 3mm ply to the flat surfaces, thought about using venetian blind slats as they're already fully finished surfaces, but are only 50mm wide [50mm wide x 3mm thick x 'whatever' high]

I played around with Tim's program during the intro month period but didn't get the 'hang of it' unfortunately, and wondered if you still have access to it to see what depth changes are required for the 50mm wide pieces instead of the 60mm wide, and for 3 or 5 modules instead of the full 7.

Sorry, my month trial on the simulator ran out long ago now. But things should just scale, if the widths are 5/6ths of some design, then the depths should just be 5/6ths of the previous depths, performance should be the same except shifted up in frequency by 6/5ths. For different numbers of modules, just stagger their depths like in Tim's articles.

There are also lighter weight plastic commercial diffusers you could buy, as well. I don't have any specific links, but some Googling should find them. Or someone may pop in here with some suggestions.
 
Thanks for the info regarding scaling the dimensions - makes it pretty simple to design - I remember one of the guys over in the 'Gearsluts' site did a design at 35mm element width but couldn't make out the change in height change - will get this organised

The Styrene surface finish cut by hot knife isn't the smoothest but slowly slicing the 600mm lengths while holding down the 75mm thick foam sheets using a plywood profile guide each end works okay - sealing the surface takes quite a few applications of PVA first and thick paint to give a firm/solid surface - trying the idea of the venetian blind slats (cheap 2nd hand source) gives a solid surface and better timber appearance without the weight - it'll be interesting how they turn out as there's always something else to complicate things.

Commercial diffusers like 'Skylines' or "Razorblades' usually come as blow moulded thin wall profile that needs filling to be effective and not cheap, none of them.

Cutting 40mm thick sheet styrene profiles, line by line (13 lines of 12 heights for basic skyline) is a hassle until getting setup - after that, it's a bit of a patience job and then the hassle of finishing/painting the rough surfaces and gluing the layers together - as you need more than one, a 'production line' is the way to go.

Tim's design is far, far simpler and even looks okay in the home environment.
 
The Styrene surface finish cut by hot knife isn't the smoothest but slowly slicing the 600mm lengths while holding down the 75mm thick foam sheets using a plywood profile guide each end works okay - sealing the surface takes quite a few applications of PVA first and thick paint to give a firm/solid surface

When I first saw this thread I thought that the treatment would be quite heavy, and I came upon the idea (not original) of making these and/or a 2D "skyline" out of wire-cut 2" styrene. Since the stuff can be quite flammable I thought perhaps a couple coats of fireproofing paint might be useful. I would probably put it behind some cloth, so looks aren't terribly important.

Got any pictures of your styrene diffuser?
 
Hey Ton,
Didn't think about the styrene's flammability - fireproof paint would do the trick - the cost is rather steep out here as still a specialty product altho disaster fires a few years ago has made it mandatory in the 'high fire' risk areas.

I did a few of the 'standard' 13 x 12 well skylines that were cut from 40mm thick sheets and grouped them together in 2s and 4s - took quite an effort, even mass producing them

Pity that you can't cover them with even an acoustically transparent cloth (this stops them acting as diffusers unfortunately) as they're a PIA to keep clean - it must be the static electricity of the styrene or something but they seem to just attract dust, lint and everything here.

I've just done a few rough blocks of Tim's easy design with the styrene profile with the 'standard' 60mm wide steps - sorting out a new profile for trying the 50mm wide version and getting the bugs out of a simple cutting table - no photos yet but some up on the 'Gearsluts' site, mostly solid timber or ply designs

One area that I still need clarification about is the ceiling 2D tiles - from the Vicoustic photos and some of Ethan's products, these are quite shallow, maybe 100mm deep, so don't know how effective these are - as the ceiling reflections are probably the most significant in most domestic situations, I would have thought this area would attract more attention - maybe the styrene versions will be light enough to experiment with ...

From memory, multiples of curved surfaces can be quite effective but have only seen these in larger areas - making them with perforated board (bent into curve) and adding absorbent material inside is an old way of doing things - the quadratic diffusers are much more effective but more trouble to make.

... my 2 cents.
 
How much better is this design then a simple curved panel?

A simple curved panel will still give a more-or-less specular reflection, so the diffused waveshape will be very similar to the direct one. Step or well diffusors diffuse both in direction and in time (waves are broken up per frequency), while a curved panel will only diffuse in direction. Is that better or worse? I'd go with step diffusor but haven't really tried both.
 
I wouldn't make the assumption that "if a 1D diffusor is good, a 2D must be better". A 2D diffusor will deflect a lot of the energy toward ceiling and floor, where it will mostly just end up getting absorbed by stuff in the room -- not a lot different than just using absorbers. A 1D diffusor can be oriented to keep most of the energy moving laterally in the room near listeners rather than only getting to them after numerous off-wall bounces.

It is difficult getting enough diffusors to keep adequate room energy, can take large units, so why make them less effective by going 2D? My "CoFusor" scheme (in this month's Linear Audio) goes further to reconcentrate (yet still diffuse, if that's not too confusing) and preserve the energy around listeners.
 
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I was looking for a solution to a problem. On my L&R side walls of my HT i have two onwall sidesurrounds. They face each other, and are about 13' apart. My concern is the slap echo/flutter between these walls and the fact that the speakers basically beam toward each other.
Would this be a good location for this type diffuser ? The room is LEDE, and maintaining energy that is diffused in the LiveEnd would be a great way, if im correct.
 
Sure, that would be a good application (though I would first try angling the speakers in a little it that's possible).

Hmmmm, angling them down would probably be good start. The bandwidth of that sound on the other wall would be narrower as it would be off axis reflection, compared to pointing directly at it......

Can i cut the 8' lenth down to 3' or what ever i need, or is the 8' height of the diffuser part of the whole design, if i worded that right :0)
 
No, 8 feet is just the length of all the lumber as-bought, so is the lowest labor method to build (no cutting, just go at it with a hammer or brad nailer -- a little yellow glue under each board isn't a bad idea in case there is ever stress on it, though).

I wouldn't go less than 3' though, think of the size of the wavelengths you need to diffuse and how much they expand between speaker and diffusor -- this particular design does well down to 400Hz, so to use that you should keep the height at least as much as the width.
 
They will work horizontally, but then will diffuse vertically, much of the energy going toward floor and ceiling where it is likely to be absorbed by stuff before working its way to your ears. A lot of people set diffusors that way, but from what I've read (and makes sense to me) that isn't too much different from just using an absorber, which might be cheaper to do or more acceptable to interior decorators.

Same with the very popular "skyline" 2D diffusors. They for the most part do about the same as an absorber in practice. The energy is thinned by diffusing both horizontally and vertically, so most just gets absorbed before getting useful, so there isn't much diffuse arrival to help the room.
 
Try making a skyline with wooden blocks and the 'fun' soon goes out of it! Very tedious!

On my project bench is my early attempt at sorting out a way to seal the surface of both a styrene skyline and a leafuser - without a ridged reflecting surface, much of the benefits are lost - hot wire cutting works quite well but still needs to be 'sealed' - PVA is the current promising material and/or exterior rendering acrylic 'paint'.

Leanfusers for horizontal dispersion (walls) and skylines for ceiling - the 'thin' commercial ones about 25- 40mm thick are only effective for treble - wide range, the thinnest are about 65mm and that's for 'wells' (those familiar blocks) about 25 - 30mm square and you need about half a metre rectangle for each first ceiling reflection point - can be quite light but need to be ridged - quite a bit of trouble, but can achieve quite excellent results