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In The Limelight

Occasional tips and how-tos from the shop at Limelight Productions ®

Theatrical Curtains and Acoustics

We frequently get inquiries regarding the possible use of theatrical curtains to control room acoustics.

First, a disclaimer: although we have fabricated and/or installed theatrical curtains in dozens of spaces ranging from multi-purpose rooms to state-of-the-art theatres, we are not acousticians. We are offering here some basic information combined with our own observations. For critical applications, we recommend that you consult a professional acoustical consultant.

Although stage curtain fabrics are typically not as effective as materials designed specifically for this purpose, they do offer some remediation and many users consider them a more attractive alternative. In addition, with the use of traveler tracks (or other rigging method), the amount and location of sound absorbing materials in a room, as well as the appearance of the room, may be altered quickly and conveniently.

Room acoustics are affected by numerous factors including the sound absorption characteristics of surfaces. We have compiled below, from several sources, absorption coefficients for various surface materials. (An absorption coefficient at a given frequency is a measure of how well a material absorbs sound at that frequency.)

Coefficient at Given Frequency
Material 128Hz 256Hz 512Hz 1024Hz 2048Hz 4096Hz Author
10oz. cotton draperies hung straight, in contact with wall .04 .05 .11 .18 .30 .44 PS
18oz. cotton draperies hung straight, in contact with wall .05 .12 .35 .45 .40 .44 PS
18oz. cotton draperies hung straight, 4 inches from wall .09 .33 .45 .52 .50 .44 PS
Rock wool , 1 inch thick .35 .49 .63 .80 .83 -- VK
Carpet (.4" thick), on concrete .09 .08 .21 .26 .27 .37 BR
Concrete (unpainted) .01 .012 .016 .019 .023 .035 VK
Wood (pine,  .8" thick) sheeting .1 .11 .10 .08 .08 .11 WS
Brick wall (painted) .012 .013 .017 .02 .023 .025 WS
Coefficient at Given Frequency
125Hz 250Hz 500Hz 1000Hz 2000Hz 4000Hz
Concrete Block , light, porous .02 .06 .14 .37 .6 .65 AS
Medium Velour, 14oz , 100% fullness .07 .31 .49 .75 .7 .6 AS
Heavy Velour, 18oz , 100% fullness .14 .35 .55 .72 .7 .65 AS
Ordinary Window Glass .35 .25 .18 .12 .07 .04 AS
½" Gypsum board nailed to 2x4's on 16" centers .013 .015 .05 .04 .07 .09 AS

PS - P.E. Sabine, VK - V.O. Knudsen, BR - Building Research Station, WS - Wallace Sabine; from Modern Recording Techniques, by David Miles Huber & Robert E. Runstein (Focal Press, 2001, see http://www.modrec.com) AS - from Acoustics 101, AcousticSurfaces, Inc. (http://www.acousticalsurfaces.com/
acoustic_IOI/101home.htm)

Low pitched sounds have a low frequency and a long wavelength. High-pitched sounds have very short wavelengths. A piano can generate sounds ranging from 20Hz (cycles per second) to 4600Hz cycles per second (Hz).

In general, curtain fabrics are much more effective at absorbing high frequencies, than low frequencies.

The human voice ranges in frequency from 87 - 1174 Hz. Speaking voices for men range between 110 - 130Hz. Speaking voices for women range between 200 - 230Hz.

Adding fullness, will increase a curtain's ability to absorb low frequencies, however curtains are not likely to approximate the effect of materials specifically designed for sound absorption.

Here are some related resources on the web:

Other Portable Alternatives

Although curtains may be the simplest way to install "adjustable" acoustics, there are many specialized products available that may be installed in ways that allow adjustment. Limelight Productions has the expertise and experience to address almost any rigging challenge.

Ozawa Hall at Tanglewood


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Limelight Productions®, Inc
471 Pleasant Street, Lee, MA 01238-9322
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