# DIY Polycylindrical diffusor ?



## F1 fan (Jul 6, 2006)

I plan to try and build a pair 2'x3' using 1/8" masonite and was wondering if a radius of aprox. 4" would suffice.Also would cutting a number of random 2" holes on the surface (and filling the area behind with mineral wool) make it an effective comboned diffusor/absorber?


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## bpape (Sep 14, 2006)

If you want diffusion, then you don't want any holes in it.

I assume you mean a 4' radius - not a 4". 

Bryan


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## F1 fan (Jul 6, 2006)

bpape said:


> If you want diffusion, then you don't want any holes in it.


Certainly ,but my thinking is that I might like to also experiment with a combination of absorbion and diffusion in one panel ( at the first reflection points) as well as straight diffusion.


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## bpape (Sep 14, 2006)

Unless you do something like a binary amplitude type diffuser, having absorpbtion and diffusion together isn't going to work. The whole point of diffusion is to scatter sound in both space and time without removing energy from the space.

The only other option would be to do some sort of grating over an absorbing panel but that wouldn't be a poly at all - simply slats of wood on the face of an absorber.

Bryan


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## F1 fan (Jul 6, 2006)

OK thanks Brian I will stick to the solid diffusor for now.Best I not link to it here but I have seen a commercial product similar to what I proposed but was'nt sure of it's potential effectiveness.I have also seen some binary devices but I assume should only be attempted given a proper formula for the hole pattern not just drilling holes at random?
By 4" radius I meant the high point at the center of the semicicle as looking from one end.


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## bpape (Sep 14, 2006)

At a side wall reflection point, if you want diffusion, I would consider doing more of a QRD type. The Poly types would be more effective on a rear wall or high in the perimeter of the space IMO.

And yes, the binary type has a very specific pattern calculation associated with it.

Bryan


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## Gregr (Nov 2, 2010)

Habs, Bryan,

I was reading about a project at Morrow Audio that may have a similar desired effect. Mr Morrow recommends gluing carpet to a sauna tube 12" to 15" in diameter. Using two 4' lengths placed between two subs in the front center stage area or two front speakers. Filling with wool, polyester or rock wool is an additional option not a must.

I thought this sounded like such an easy project that it is a must try. Bryan what is your impression of this idea. I am sure commercial products are easier still but do the potential benefits make this worth trying.

Thanks


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## bpape (Sep 14, 2006)

Carpet on the outside will be absorbent. The mids between the range where the carpet absorbs and where the wavelength swamps the diameter of the tube will be scattered (not diffused) but better than a flat surface.

Below that you may get some control in the bottom end depending on the diameter of the tube, it's density, how it's going to resonate, etc.

Bryan


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