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Perfecting sound with acoustical fabrics

February 1st, 2020 / By: / Feature

Fabric applications create acoustic environments that control sound, allowing the featured entertainment to be clearly heard. 

by Sigrid Tournquist

Fabric plays a critical role in sound control. On the most basic level, hard surfaces send sound bouncing around a room, while soft surfaces absorb sound and soften the impact on listening ears. For environments designed for entertainment, sound control heightens the experience for anyone sitting in the audience.

“Controlling sound waves is not so different than controlling light—you have to deal with the reflections,” says Joshua Alemany, director of products, Rose Brand, Secaucus, N.J. “Fabric is a versatile tool in that it can easily adjust from a flat surface, which can be reflective or absorptive depending on the textile, to a contoured surface, which reflects the sound waves in different direction, scattering and nullifying the reflections.”

Paul Grider, director of product development and technical services, Dazian LLC, South Hackensack, N.J., says that to manufacture acoustical drapery, one must have a good understanding of sewing styles and techniques along with fabric knowledge and installation methods. “Knowing what your client is looking to achieve is the first step in selecting the right material. From there, we access the space conditions and installation options,” he says.

Stages Consultants helped architectural firm Henning Larsen and theater equipment manufacturer Waagner-Biro develop an application for wool serge used as sound absorptive banners for the Harpa concert hall in Reykjavik, Iceland. Here, the banners, developed by Chris Darland, extend on the rear wall above the control room. Acoustics and theater planning by Artec Consultants Inc. Photo: Damian Doria, Stages Consultants.

Absorptive finishes

Damian Doria, president of theater and acoustics design consultancy Stages Consultants, Highland Park, N.J., breaks down acoustical applications into three categories: absorptive finishes, protective covers for absorptive finishes, and barrier materials.

When selecting fabric as an absorptive finish, Doria recommends taking into account absorption coefficients, measured using a standard laboratory method: Octave Band Absorption Coefficients and Noise Reduction Coefficient (NRC). “It’s also important to disclose the test method and mounting for the material because, as an example, a material that’s mounted over an air space performs differently from material pressed flat against a surface,” Doria says. “Since we’re often talking about curtains, it’s helpful if the original test report is available to learn whether the fabric tested had any special treatment or backing, was a flat panel or had some degree of fullness, the type of pleating, etc.”

Most often, curtains are used to reduce the unwanted sound reflections that cause excessive noise or distortions, Alemany says. “Fabrics of a heavy weight or specific construction can be used to absorb sounds, usually targeting the low frequencies that create troublesome acoustic resonances,” he says. “Alternately, lighter weight fabrics hung in fullness (pleated) can accomplish similar deadening.”

Well-designed curtains reduce unwanted sound reflections that cause excessive noise or distortions in performance spaces. These window curtains made from Rose Brand Prestige Velour serve both aesthetic and acoustic purposes at Mason Hall at Baruch Performing Arts Center in New York City. Photo: Rose Brand.

Two factors contribute to the amount of sound absorbency a fabric can provide, according to Cheryl Warren, president, Chicago Canvas & Supply, Chicago, Ill. “The first is the density of the pile, with more being better,” she says. “For the second, such as in the case of a curtain, the more pleats or gathered material within a space, the more effective the sound absorbency. We generally recommend two fabrics: a cotton flame-retardant called Sound Absorber and velour for stage curtains.” 

The most commonly used weight options for velour range from 15 to 25 ounces, Grider says. When a client needed to divide an exhibit floor from an awards show that was taking place at the same time in the same space, Dazian used a 16-ounce velour made into a drape with knife pleats and 50 percent fullness for a 780-foot-wide by 16-foot-high partition. “The partition needed to be freestanding and put up in less than six hours—and our team did it in less than four,” Grider says. “The drapery provided the client with the perfect amount of sound absorption for both events to function simultaneously in one shared space.”

Protective covers for absorptive finishes

Fabric stretched over an absorptive core can act as a protective cover and an aesthetic cover. One of the key elements of how the protective cover functions is its level of porosity. “Typically, high-porosity fabrics are preferable, but some less porous fabrics are good acoustical performers when stretched over an absorptive core material and tend to be more durable than more porous fabrics,” Doria says. 

Materials differ depending on the environment, such as whether the space is climate controlled or how durable the fabric needs to be. “Typically, polyester fabric is used for fabric-wrapped wall panels or fabric stretch systems that are common in commercial environments that are climate controlled—classrooms, training rooms, auditoriums,” says Gary Hudson, vice president of sales, Acoustical Solutions, Richmond, Va. “PVC might be used in ceilings, as baffles and banners in aquatic centers, while ripstop nylon is used on panels in gymnasiums so that when balls hit them, the fabric doesn’t blow out as it would with heat-sealed PVC.”

Successful manufacturers of acoustical fabric products understand what the client needs and how fabric can provide a solution. For this recording studio, Dazian installed wall-mounted acoustical panels and drapery to decrease the intensity of echoes and noise within the space. Photo: Dazian LLC.

For upscale climate-controlled environments in which aesthetics are paramount, color matching is also a key consideration. When one of New York City’s premier event centers in Manhattan had a severe problem with unmitigated sound reflections, the echo and reverberation in the space resulted in some very unhappy rental clients. “No amount of sound-system electronic tweaking could help guests hear the beautifully spoken comments of the father of the bride,” says John Calder, media producer at Acoustical Surfaces Inc., Chaska, Minn. “We designed large stone-column-like sound diffusers with internal sound absorption that would break up and reduce the ‘echoey’ sound-lens effect of the beautiful room’s high oval shape.”

However, one of the keys to the client accepting the final design was that the covering fabric color-matched the limestone walls that had helped place the facility on the National Register of Historic Places. “As it turned out, nearly no one noticed that more than a dozen 4-foot-wide by 12-foot-high diffusers had been added to the walls, due to the accuracy of the fabric match,” Calder says. 

To abate a terrible echo and sound that bled into hallways in a renovated conference room in Broken Arrow, Okla., Acoustical Solutions used a combination of art panels with pictures of historical Broken Arrow and standard AlphaSorb® fabric panels. This solution eliminated the need for additional art pieces in the room while improving the acoustics. Photo: Acoustical Solutions.

Barrier materials

Barrier materials fall under the sound-proofing category as opposed to sound absorptive. “Sound proofing is more about sound blocking or lessening the noise coming into a space,” Hudson says. 

“When using fabrics as a barrier material, we are looking for a fabric that is not porous or is minimally porous,” Doria says. “There are a few products in the marketplace promoting their use as sound barriers, and they will report Sound Transmission Class (STC) [an integer rating of how well a building partition attenuates airborne sound] and Octave Band Transmission Loss (TL) [a tool for measuring the insulating properties of walls, floors or doors separating two rooms] based on standard laboratory testing.”

Acoustical Surfaces designed stone-column-like sound diffusers to match limestone walls at The Gotham Center for New York City History, a research and public education institution on the National Register of Historic Places. Photo: Acoustical Surfaces Inc.

Adjustable acoustics: What about wool?

Perhaps the oldest workhorse fabric for theatrical acoustics is wool serge, which has long been used for sound absorptive banners. And with creative application, the banners can provide a level of adaptability to accommodate a range of different performance types. “In some performance spaces, fabrics are a key part of ‘adjustable acoustics’ systems that may be extended or retracted to vary reverberation in a room, making it better suited to a narrow range of activities or suited to a broader range of activities,” Doria says.

That is exactly what Stages accomplished when it helped architectural firm Henning Larsen and theater equipment manufacturer Waagner-Biro develop an application for wool serge used as sound absorptive banners for the Harpa concert hall in Reykjavik, Iceland. The visually flat panel of fabric rolls up into a small space in soffits around the perimeter of the concert hall’s seating, using tube motors similar to those used in retractable awnings for patios. 

Secondary chambers also include wool serge banners and can be coupled to the main hall through operable doors. “These features create the ability to change the absorptive character of most of the walls in the room and either lengthen or shorten the reverberation time while increasing or decreasing the loudness of that reverberation—allowing a range of performances from organ, chorale, symphonic opera and recital works to highly amplified popular music—with only a short time to readjust the room’s settings between events,” Doria says.

Whether a space calls for sound absorption, sound blocking or sound diffusion, the right fabric in the right design can guide sound energy—and create an acoustic environment that sounds just right. 

Sigrid Tornquist is a Minneapolis-based writer and editor, and a frequent contributor to Review.

SIDEBAR: Growth alert! Home theaters

According to Market Research Future, the home theater market will have a compound annual growth rate (CAGR) of 19 percent from 2016 to 2023—which also spells growth for acoustic fabric suppliers and end product manufacturers. The range of fabric treatment opportunities spans the gamut depending on the client’s budget. 

“The average consumer can purchase a low-cost projector or HDTV with an integrated amplifier packaged with a set of small speakers and create a terrific experience without ever doing much more than furnishing their family room or den with some carpet, sofa and some window curtains,” says Damian Doria, president of theater and acoustics design consultancy Stages Consultants, Highland Park, N.J. 

“Consumers seeking a more professional screening room or cinema experience are more likely to seek online advice or professional design assistance in selecting equipment and finishes. In those spaces, we can see a lot of fabric treatments—a baffle wall at the screen to hide speakers, curtains or acoustic panels on the walls, and even fabric-treated ceilings.”

SIDEBAR: Reverb defined

ABOVE: Acoustical Solutions planned and installed the acoustical treatment to prevent transmission of foreign sound into this university mixing room, as well as keep the room as sound absorbent and silent as possible. The walls of the mixing room are an AcoustiWall Fabric Stretch System, which provides floor to ceiling sound absorption, preventing reverberation and deadening the space. Photo: Acoustical Solutions.

Controlling sound boils down to reducing reverberation. Gary Hudson, vice president of sales, Acoustical Solutions, Richmond, Va., describes “reverb time” as what most people would perceive as echo. “For example, you walk into a gym and clap your hands and hear that clap go on for three, four, five seconds,” he says. “Reverberation time of more than two seconds is what creates a lot of indirect sound, which interferes with the direct sound that you’re trying to make audible or more intelligible.”

According to a 2016 HyperPhysics presentation by Georgia State University Department of Physics and Astronomy, “The reverberant sound in an auditorium dies away with time as the sound energy is absorbed by multiple interactions with the surfaces of the room. In a more reflective room, it will take longer for the sound to die away, and the room is said to be ‘live.’ In a very absorbent room, the sound will die away quickly and the room will be described as acoustically ‘dead.’”