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RE: hanging diffusor: ---any ideas?

Posted by David Aiken (A) on December 31, 2008 at 19:50:44

In Reply to: hanging diffusor: ---any ideas? posted by rhyno on December 31, 2008 at 14:13:29:

Why hanging, and hanging from what?

Most diffusors tend to be bulky and heavy and wall mounted so I'll assume that you don't want bulky or heavy since you don't want wall mounted. That tends to reduce options drastically.

If you remember the Argent Room Lens, there's no reason you couldn't hang an array of pipes a few inches in front of the wall. You could stuff the pipes with insulation and get a little bit of benefit from them as Helmholtz resonators, and vary the spacing between the pipes slightly as well as their diameters in order to introduce a little visual variety. Alternatively you could use round polished wood rods about 2-3" in diameter for the appearance. The advantage of this approach is that not only the round surfaces of the pipes act to spread sound but diffraction spreads the sound passing through the gaps between the pipes so you get benefit from that as well.

There are some panel diffusors like RPG's BAD panel which rely on a sheet of reflective material with perforations in it in a random or mathematically calculated pattern for diffusive effects. There's also absorptive material behind the reflective sheet so the BAD panel functions as an absorber as well. I think RPG also make a bass trap out of clear acrylic which is simply a perforated panel to be hung/spaced away from the wall. I assume it acts as a Helmholtz resonator or operates on some similar principle but I wonder whether you would also get some diffusive effects from a similar panel with holes in a similar pattern to that of the BAD panel. I haven't seen anyone attempt to produce a diffusor made that way but I have seen a description somewhere of a diffusor/absorber panel made with a curved front panel of plywood with a random pattern of perforations and with absorptive material in the cavity of the panel. That design would probably be too heavy to hang easily.

A final alternative, since curved surfaces scatter reflections which promotes diffusion, would be an array of hanging spheres of various diameters, suspended at various heights and spacings to produce some sort of pleasing pattern. Things like fishing net floats and similar spherical objects could be used. The advantage of using spheres is that the gaps aren't all vertically aligned as they would be with rods and that can help introduce some vertical variation into the scatter pattern.

Ideally I'd suggest using objects (pipes, spheres, whatever) which are curved on the rear side as well since as sound passes through the gaps towards the wall it will spread out due to diffraction and then be reflected back into the room from a wider wall area than would have been the case without the objects. Some of that reflected sound will strike the back of the objects so curving the back ensures that those reflections are scattered again, perhaps several times, before eventually reflecting back into the room through the gaps and from the sides of the hanging array.

You could probably increase the scattering a little more by gluing some flexible plastic tubing in spirals around the pipes/rods, or in curved patterns around the spheres.

Basically the simplest approach is to look for curved surfaces that you can hang, and go for as much variety in the size of the surface and the spacing between adjacent surfaces as you can manage given that you want to put a reasonable number of those surfaces into a relatively close area. If you can also vary the distance between the back of the objects and the wall, that should help as well. You could hang spheres or cylinders of different diameters so that there was the same distance between the closest part of the objects to the wall and the wall, but the hanging points which will be above the centre of each object will be different distances from the wall and the fronts of each object will be different distances from the wall. Basically trying to get a non-uniform pattern of surfaces is the goal.

Alternatively you could try to construct a skyline diffusor type object with square lengths of wood of the same length glued together so that the ends of each piece are at different heights relative to adjacent pieces. That will result in front and back surfaces which are kind of like reverse mirror images of each other but also means the weight will be symmetrically distributed front to back making it easy to hang vertically. The only problem will be weight. I guess you could use a very light wood like balsa but I think that could work out expensive for a panel of any really useful size.

Aesthetics is really going to be up to your choice of objects, painting choices, etc.

That's about the end of my ideas. I know of no commercial diffusor products intended for hanging.




David Aiken

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