Recording - September 2014 - 63

Figure 2. Arrays of polycylindrical diffusors at the back and side walls of Captain Audio, Burbank, CA,
designed by the author. Special thanks to Todd Niesen.
are available at construction supply companies, but you
can also find some of the smaller ones at home centers,
and even Amazon. Some sample brands are the
Sonotube by Sonoco, the Form Tube by Sakrete, and
(shown in Figure 3) the Quik-Tube by Quikrete.
Another way to make a polycylindrical is to take a
sheet of 1/8" plywood ("lauan door skin"), 1/4" plywood, or Masonite, and bend it into a curve. Some 1"
x 2" furring strips across the width can be used to both
hold the sheet in its curved shape and provide a place
for hooks or eyes to attach it to the ceiling or suspend
it. Figure 4 shows one possible design.
Polycylindricals do have one useful characteristic that
QRDs don't. You can cover them with pretty much anything
you want-cloth, paint, carpet, whatever. That means you
can also put a layer of absorbent on them, like the everpopular Owens-Corning 703 semi-rigid fiberglass panel,
and then cover that with an acoustically transparent fabric
like Guilford of Maine FR701. Johns Manville Microlite will
also work well. If you stick with 1" thick 703 and don't put

too severe a bend in the plywood or Masonite, the fiberglass should conform to the curve of the polycylindrical just
fine. You can also cut V-shaped grooves in the back of the
703 to help it take the shape. Remember to wear gloves
and breathing protection when working with the 703.
Now, if having anything like that over your head makes
you uncomfortable, you can still use regular absorption
rather than diffusion as a fallback position. My first pick
would be a 2" thick panel of O-C 703, also covered with
acoustically transparent fabric. There is even specialty hardware for suspending fiberglass board like 703. RotoFast
Cloud Anchors (www.rotofast.com) screw directly into the
703, and have an eye to suspend them from the ceiling, as
shown in Figure 5. RotoFast makes different models for
attaching 703 panels to other room surfaces.
Figure 3. These tubes are used for shaping poured
concrete until it hardens, but if you cut sections of
them lengthwise, they can be turned into
polycylindrical diffusors.

Figure 4. A design for a polycylindrical
diffusor made from curved sheeting.

RECORDING September 2014

63


http://www.rotofast.com

Recording - September 2014

Table of Contents for the Digital Edition of Recording - September 2014

Contents
Recording - September 2014 - Cover1
Recording - September 2014 - Cover2
Recording - September 2014 - 1
Recording - September 2014 - 2
Recording - September 2014 - 3
Recording - September 2014 - 4
Recording - September 2014 - 5
Recording - September 2014 - Contents
Recording - September 2014 - 7
Recording - September 2014 - 8
Recording - September 2014 - 9
Recording - September 2014 - 10
Recording - September 2014 - 11
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Recording - September 2014 - Cover3
Recording - September 2014 - Cover4
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