We start things a day early and go into greater detail about the intricacies of a true polycylindrical diffuser. And, of course, show off some more cool ripple tank creations.
You have played with it, right?
“Poly” Want a Cracker?
Polys are formed by a shallow sections of a cylinder. This has ideal curvature all the way across with no hard corners.
A half section of a cylinder is not a poly. It has undesirable reflection patterns when mounted against a hard surface (wall)*.
A half cylinder has two parts: a curved poly part (good) and a corner part (bad). Corner reflections don’t scatter, they reflect right back where they came from.
A corner reflection is useful if you are a surveyor but not in the world of sound diffusion.
*TubeTrap diffusers are hemi-cylindrical polys mounted atop broadband absorbers, therefore they do not create these hard corners. This is also why diffusers are smaller on HalfRound and QuarterRound TubeTraps.
Part 2: Now the Wavefront Has Expanded All the Way to the Polys. The Diffusion Has Begun!
DIY Diffuser (so easy!)
This is so easy to build, it’s hard not to build it. Try, we dare you!
Get a thin flat panel that is a little wider than the backboard.
DIY Diffuser (so fun!)
Bend the panel and snap it onto the backboard. See, you’re probably already done!
But is This a Poly?
Not exactly. This is a catenary which is rounded in the middle third but flat on the other two side sections.
The result is a sound spreading diffuse surface in the middle section and two beaming reflections off either side. No, not perfect, but at least the beaming sections are probably not parallel to your walls or speaker baffles (good).
Part 3: A soft, smooth diffuse field returns
At the front of the room and sounds just like it would in an acoustically treated symphony hall