Poly Diffuser - Help Please

[MusEsq]

I am building some Poly diffusers for the back wall of my mix/writing room. I need bass absorbtion on the back wall as well.

I have read that I should pack the cavity behind the poly diffuser with fiberglass. I have some 2" 703 - so, should I cut, stack and pack it in the cavity, OR, should I just get some Owens Corning pink insulation and pack it?

Also, should the insulation actually touch the back of the bent wood, or should it be left free to resonate.

Bass absorbion is really needed, but the "one who must be obeyed" doesn't want any more standard traps in the room.

Any help would be appreciated! Thanks!

[RKrizman]

I'm interested in this as well.

-R

[johndykstra]

Based on designs that Andre (avare) helped me with, you want the insulation touching the panel. This may have been a specific recipe for my room, so I guess I don't know why i bother posting this, other than to add a subscription to all things poly. The build thread for the polys is in my signature line... if you're interested.

[MusEsq]

I now recall reviewing your excellent post(s) regarding your studio build. I am dizzy with information! Thank you (and Andre) for clarifying the insulation against poly curve mystery.

Your build is especially beautiful. What kind of wood did you use?

I built mine in a frame (without a back), so I will have to stuff insulation in it
from behind. It is going to get interesting!.

Thank you so much for your help. Nice studio!!!

[johndykstra]

Hey Thanks.

Regarding the wood type, I really don't know. It was wood from the back of traps that I removed and reused. it's 1/8" thick... I know that.

[Glenn Kuras]

You can use either.

[Bannny]

I have been researching poly diffusers a bit and want to build some for my 19x19x13 live room. I have never bent plywood, but it seems a bit involved.

I am wondering if maybe cutting some crappy drum shells in half might be an easy solution?

[johndykstra]

Hey there.

1/3 a circle is the optimum arc for a poly diffusor. You would want to cut drum shells in thirds.

It's really not all that difficult, just use thin wood

[Bannny]

Originally Posted by johndykstra

Hey there.

1/3 a circle is the optimum arc for a poly diffusor. You would want to cut drum shells in thirds.

It's really not all that difficult, just use thin wood

I thought that thicker was better. I guess I will try some thin plywood first then. Thx

[Torea]

Originally Posted by Bannny

I thought that thicker was better. I guess I will try some thin plywood first then. Thx

I wonder if solid wood be easier to bend. It's a bit more expensive, but I would think the individual plys would start to have some issues as you bent them. I'm not a woodworker at all, just seems like ply might disagree with being bent.

[hsal]

You can get special ply designed for bending, it has grain deriction and glue that is benificial for bending.

It costs 3-4 times more than normal ply.

One can ask a local cabinetworker if it is hard to get.

Solid wood bending is a craft.

[hsal]

Just to add, it is possible to make poly diffusors with normal (thin) ply aswell, but for very narrow designs, for instance 30 cm wide 10cm deep, one has to use special ply.

One can add sorbothane, or glue strips of wood to the backing in order to dampen/change resonance frequensy.

[Bannny]

well, now it seems like cutting up the drums would be easier than messing around, trying to bend wood, and keep it bent.

[hsal]

Keeping it bend is not a problem, look at the picture in op`s post, the most important factor in my opinion is to vary the width/debth ,the idea is to avoid rhytmic reflections and strong lobing at certain frequensies.

You can also put them side by side, there will be a focusing effect between polys, but if the polys has a good curve the focus area is very close to the wall, using normal micing techniques this will not be a problem.