skyline diffusers, math involved?

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gianelli280

gianelli280

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I came across a ton of foam and wanted to know if there is a specific design most block-style "skyline" acoustic diffusers use? Save your flame, i know foam sucks, foam sucks, foam sucks. It just seems like the most suitable material to use for my application.

I plan on using 4x4'' sections (too big?) and varying depth between 2-7 inches. I've heard that 3'' depth at least for diffusers, but does that count as 3'' from the tallest to shortest block, or 3'' from the mounting surface?

thanks!
 
What kind of foam are you talking about?

Open cell foam is good for absorbers (ie; Auralex)

Hard foam is fine for diffusors... like Owens/Corning Formular 150. this stuff is used as insulation behind siding, concrete work, etc. It can be purchased in thicknesses ranging from 1/2" to 2" or so.

For PRDs I would recommend using Oliver Prime's online calculator here.

If you are attempting to use soft open cell foam for a diffusor, you will be wasting your time. This is not an opinion.

Also 4" by 4" sections of hard surface diffuses up to 848Hz --- that is the highest frequency that it will properly diffuse. Higher than that 'cutoff' frequency the diffusion coefficient drops. --- With a diffusor depth of 7 inches, the low frequency cut off will be 969Hz... below that the efficiency drops as well.
So there -- you have a diffusor that does not operate well as a diffusor.

Personally I would never recommend a PRD with a block size smaller than 2" - Peter D'Antonio doesn't either - unless it's a part of a larger or smaller PRD. think Diffractal.

I would suggest using 2" or 1". 2" = 1.6kHz hf cut off & 1" = 3.4kHz hf cut off. ;)

Cheers,
John
 
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Wow, Thank you!! That's exactly what I needed to hear! Unfortunately i have no idea what kind of foam it is, i'll try to look it up but it more than likely is soft open cell i'm assuming.

So the dimensions you suggested, those are height/width, correct?
 
Height and width, yes.

Bro, if it is the soft stuff. Forget it. You've got a lot of foam for absorption panels. :P

-- John
 
hah, i'll just say the craigslist description was "great for a foam pit" Absorption panels you say?
 
Just out of curiosity, can you squeeze or condence the foam so that it's density approaches the efficient 50kg/m3 to get absorbtion?

Or does it really come down to the type of foam structure?

FM
 
pure.fusion said:
Just out of curiosity, can you squeeze or condence the foam so that it's density approaches the efficient 50kg/m3 to get absorbtion?

Or does it really come down to the type of foam structure?

FM
Click to expand...

Not really.
Open cell acoustic foam has certain properties which, I do not believe, can be adjusted by 'squishing'. We're getting into 'gas flow resistivity', cell wall thickness, etc.. which all play a part in making a good absorption foam. I do not have the data on what is the 'ideal' foam absorber. - I do not believe that this is something that would be worth the time to experiment with because it is cheap enough to buy the 'good stuff' from Auralex and companies like them. ;)

I, personally, am not a big fan of foam. But for the right application at the right price, many times it can't be beat. It's quick & simple to install and effective for it's recommended application.

Cheers,
John
 
foam is not a diffuser, foam is an absorber. 2 totally different things. and yes, the right built skyline diffuser involves math.
 
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