Poly-cylindrical diffuser material

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Poly-cylindrical diffuser material

Postby jonc19 » Wed Jan 25, 2017 1:29 pm

Hi,

I'm looking to build some relatively cheap poly-cylindrical diffusers, and so far I have thought of two options:

1) I have sourced some concrete forming tubes that are already cut into half cylinders.

2) I could bend some 3mm pegboard/hardboard (or possibly plywood, not as cheap): a cheap option I thought of was to bend it by attaching wire to holes at either side and then tensioning the wire to bend the material, but in this case it would not be mounted in a frame, which I gather is desirable.

The pre-cut concrete forming tubes seems like a quick option, however, larely due to shipping costs it is 2-3x more expensive than option 2. In addition, from the FAQ it is clear that a Euler-Bernoulli buckled curve, or the ability to make curvatures of different radius, is favoured over cylinder sections. In that case, I could happily go with option 2, but, two questions:

Does the density/thickness of the material matter for this sort of design? I am not sure of the density of the cardboard material (option 1), but they are 9mm thick and each half-tube weighs ~6kg, so they are pretty bulky things in comparison to the pegboard, and secondly, will the holes in the pegboard be a problem?

This is my first post, so to introduce the space I am trying to treat, it is 5.5 x 3.75 x 2.2 m. It is currently treated with bass traps and broadband absorption (Rockwool) - this got rid of the flutter echo, but it is now sounding a little "dead", hence my interest in diffusers.

Thanks
Jon.
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Re: Poly-cylindrical diffuser material

Postby bert stoltenborg » Fri Jan 27, 2017 11:16 am

The material shouldn't be to light/thin. Th E-B plates Scott and I measured are of heavy plastic 9 mm thick.
Holes in the plates can turn them into tuned absorbers.

However, I think diffusion is for spreading sound in rooms where you have more listeners.
You could, to liven things up in your room, go for some reflective foil over your bass traps
If you view life with the knowledge that there are no problems, only opportunities, you are a marketing manager.......this is my personal philosophy
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Re: Poly-cylindrical diffuser material

Postby jonc19 » Fri Jan 27, 2017 4:47 pm

Thanks,

That sounds good. I previously bought adhesive foil tape - so perhaps that's the first focus. I'll try the foil tape adhered to the front of the bass traps (straight against the Rockwool behind the fabric), hopefully that will liven things up a bit.

OTOH, the guy said he could now give me the 6 x 9mm cardboard half-tubes for £50 incl. shipping (cheap for the UK) as they are otherwise just laying around - tempted to get them and just try it out at that price. That is if the half cylinder is not substantially worse than an E-B curve. Do you think it's worth giving it a go? Very little effort needed since they are already cut.

Is it worth it if I can't have curves of different radius? But instead half-cylinders e.g. like https://www.lifewire.com/make-your-own- ... er-3134903

Thanks again
jonc19
 
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Re: Poly-cylindrical diffuser material

Postby bert stoltenborg » Mon Jan 30, 2017 2:19 pm

A half-cylinder spreads sound in a more even way than a lot of different sized cylinders (more an approach like a QRD).
Here is an paper about that: viewtopic.php?f=8&t=3831
People like Floyd Toole advocate reflections to be as close to the original signal as possible, so extreme corrugated surfaces should be avoided in this view.

If you don't care about the money any experiment is a nice adventure, in my opinion :) .
If you view life with the knowledge that there are no problems, only opportunities, you are a marketing manager.......this is my personal philosophy
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