Controlling sound in exposed structure spaces

by Sarah Said | October 18, 2018 4:29 pm

by Sean D. Browne

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Current design trends often call for exposed structure spaces where there is no ceiling plenum and building service elements such as ductwork and piping are visible overhead.

Sometimes called the “warehouse look,” exposed structure spaces often experience acoustical problems due to excessive sound reflection off the hard roof deck surface and the added volume of the space. Conversations, activity sounds, and HVAC operations will all contribute to excessive noise and reverberation. Reflections off the deck between cubicles in open plan office environments can cause distractions for nearby occupants. As a result, exposed structure spaces usually need some type of sound absorbing elements to control noise and reverberation.

Many noise issues related to exposed structure designs can be addressed through the use of acoustical ceiling clouds, canopies, and shapes. These three types of “free-floating” options absorb sound on both their front and back surfaces. Direct-to-deck panels, vertical panels, and acoustical roof decks can also provide much-needed acoustical absorption in these reverberant spaces.

Acoustical clouds
Created for use in either new construction or retrofit applications, acoustical clouds are an ideal way to define spaces in an exposed structure and enhance acoustics without sacrificing design flexibility. When suspended above work areas, acoustical clouds provide a type of interrupted ceiling plane. As such, they help control both reflections between cubicles and distant reverberation, thereby reducing occupant annoyance and distractions.

Acoustical ceiling clouds are available in a variety of standard sizes, ranging from 2 x 2 m (6 x 6 ft) to 4 x 4 m (14 x 14 ft). Standard shapes range from squares, circles, and rectangles to hexagons, trapezoids, and convex or concave panels. Custom sizes and shapes are also available.

A typical cloud system consists of 0.6 x 0.6 m (2 x 2 ft) ceiling panels with factory finished, pre-cut corners and a separate kit containing all the pre-cut-to-length, ready-to-assemble suspension system and perimeter trim components required to create the cloud. The choice of ceiling panel in the cloud includes mineral fiber, fiberglass, wood fiber, or perforated metal panels.

Acoustical clouds are normally installed in a standard 25-mm (¹⁵/16 in.) grid system. Today, installation systems reduce the number of hanger wires and recess them from the perimeter edges, making the hangers less visible and producing a more dramatic, “free-floating” look for the cloud. Building services such as HVAC, lighting, sound masking, and sprinklers can be cut into the acoustical clouds just like a traditional wall-to-wall ceiling system. However, due to the discontinuous nature of acoustical clouds, existing building service elements can often be installed in between the clouds, allowing for easier retrofit capability.

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Case study
The Customer Experience Center (CEC) at the GE Advanced Manufacturing Works in Greenville, South Carolina, not only showcases GE manufacturing advancements but also hosts a multitude of corporate events. As a result, the design team at MCA Architecture in Greenville looked to create a multifunctional, exposed structure space that was both dynamic and energetic.

To meet the design intention, the team selected acoustical clouds. According to project architect, Michael Kissam, clouds were selected for several reasons.

“First,” he says, “we were looking for a ceiling treatment that was not static or overbearing but evoked a sense of movement, dynamism, and progression. Second, we were under an extremely aggressive schedule that had to be completed in nine months from design to client occupancy. The cloud kits provided a unique advantage because the clouds could be fabricated at ground level and raised to their finish elevations at the last moment. This installation sequence allowed for the overhead utility work to be completed while mitigating the ceiling grid and tile damage that is a reoccurring problem for typical project close-outs.”

He also reports acoustics was a key consideration because the CEC is designed to accommodate a variety of different functions.

“The majority of the surfaces are glass walls and ceramic tile, so the ceiling was our only opportunity to control the acoustics,” he explains. “By layering and overlapping the clouds, the ceiling created a baffling effect that proved to be highly effective.”

In total, 53 circular clouds ranging in diameter from 2 to 4 m (6 to 14 ft) were installed in the CEC.

“The finished product and function of the acoustical clouds exceeded our design intention and, more importantly, the client’s expectations,” he says.

Wood fiber roof decks offer acoustic control

Acoustical clouds, shapes, baffles, and blades made from cementitious wood fiber help control noise in exposed structure spaces. Structural acoustical roof decks made from cementitious wood fiber can do the same.Cementitious wood fiber roof decks are available in a variety of composite and non-composite panels in plank or tile configurations to address a building’s design requirements. Both types of panels are usually made of rapidly renewable aspen wood fiber bonded with an inorganic hydraulic cement. They offer a noise reduction coefficient (NRC) up to 0.80 to provide predictable acoustical performance, often eliminating the need for additional noise reducing materials. Both feature a textured interior finish.The panels are a potential noise reduction solution for large, high traffic, exposed structure spaces such as auditoriums, gymnasiums, arenas, pools, and multi-use facilities. They also help meet the Leadership in Energy and Environmental Design (LEED) and the American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE) requirements for spaces such as gymnasiums and auditoriums.Non-composite panels are typically used in low-slope applications, are compatible with virtually all roofing materials, and provide a thermal barrier for field-applied foam plastics. They also meet stringent sustainability criteria, including environmental product declaration (EPD), health product declaration (HPD), and Declare. Composite roof deck panels are typically used in sloped applications where acoustics, insulation (R values up to 44), a nailable surface, and structural integrity are all required. By providing all these features in one panel, wood fiber composite roof decks are faster and easier to install than the multistep installation of steel deck systems.

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Acoustical shapes
Acoustical shapes are similar to acoustical clouds, but consist of only a single panel. Ceiling grid elements or perimeter trim are not required. The portfolio includes a multitude of standard shapes, ranging from squares, rectangles, and circles to trapezoids, hexagons, and both convex and concave contours. Custom shapes are also available as well as standard and custom colors.

Designed for use in exposed structures and other areas requiring spot acoustics, acoustical shapes can be installed as individual units or grouped together to create innovative visual combinations helping define the area below.

Acoustical shapes are quick and easy to install and adjust to desired hanging heights and angles. Installation does not require special tools or techniques. The panels are simply suspended from the building structure using a hanging system. The hangers are made from aircraft cable to provide a sleek, clean finished appearance. All hardware, cables, and other required installation components are usually packaged with each panel.

Case study
To house students in a unique, new interdisciplinary curriculum, officials at Zionsville High School in Zionsville, Indiana, decided to renovate an existing 836-m² (9000-sf) warehouse that had no interior walls and an exposed structure.

“The design challenge became how to define areas within such a large space without building walls,” says project architect, Allen Cradler, of Fanning Howey, Indianapolis, Indiana. “Using the floor was a possibility, but it was definitely the ceiling plane that offered the most opportunity.”

Another aspect of the challenge was to design an eye-catching ceiling with a custom look, but create it with standard products to stay within budget.

To attain the desired aesthetics and acoustics, the design team selected acoustical shapes. The panels were offered in 10 geometric shapes, allowing Cradler to use different shapes to define individual areas.

Groups of convex and concave panels were placed over student work areas, while circles were featured in the entryway, and combinations of squares and rectangles highlight the pathways. By the time the ceiling design was complete, Cradler utilized five different shapes in 36 groupings, totaling 155 individual panels.

“Another feature we liked was the shapes came out of the box finished and ready to go,” Cradler says. “All we had to do is hang them. Ease of installation was a definite factor.”

Acoustical canopies
Acoustical canopies also reduce noise and reverberation time in the space below them, but are very different in size and look compared to acoustical clouds. In terms of size, pre-packaged cloud systems are usually available in squares and rectangles ranging from 2 x 2 m to 4 x 4 m, while acoustical canopies are generally smaller ranging from 1 x 1 m (3 x 3 ft) to 1.2 x 2 m (4 x 6 ft).

Visually, acoustical clouds are flat, while canopies are curved and can be installed as hills or valleys. The most common acoustical canopies are made from mineral fiber. Wood and metal canopies are also available, but must be perforated and backed with an acoustical fleece to obtain the desired acoustical performance.

The ability of canopies to combine an aesthetically pleasing visual with sound absorbing properties that provide spot acoustics makes them ideal for use in exposed structures as well as over individual spaces such as workstations and reception desks.

Installation is easy, requiring no special tools or techniques. The canopies are simply suspended from the building structure. In addition, all hardware, cables, and other required installation components are normally packaged with each canopy.

Direct-to-deck panels
In addition to the use of “free-floating” ceilings, noise issues related to exposed structure designs can also be addressed in several other ways, including acoustic elements that attach close to the exposed deck. Called direct-to-deck or direct-attach ceilings, these panels are specifically designed to maintain the look and feel of exposed structure designs while providing excellent sound absorption. They are offered in three versions: mineral fiber, fiberglass, and cementitious wood fiber.

Most mineral fiber direct-to-deck ceiling panels have a noise reduction coefficient (NRC) of 0.75, meaning they absorb 75 percent of incident sound. They are fast and easy to install on hat tracks or furring strips, and cut easily to fit any space. Aesthetically, the panels attach to the deck of an exposed structure space, allowing them to provide acoustical absorption while virtually disappearing into the space.

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Ideal for use when retrofitting or making acoustical corrections to existing spaces, the panels usually measure 0.6 x 1.2 m (2 x 4 ft) in size and are available in white, black, and field paintable. Field paintable panels have an unfinished, factory applied scrim that can be painted to match the deck while still maintaining their acoustical properties.

Fiberglass direct-to-deck panels feature an exceptionally high NRC of 0.90. As a result, when installed over only 20 percent of an area they can reduce unwanted reverberation by 50 percent.

Ideal for use in new construction, fiberglass panels are also a simple, affordable way to retrofit poor acoustic-performing exposed structure spaces. They are especially well suited for open offices, educational spaces such as labs, cafeterias, and gymnasiums, and retail establishments.

The lightweight panels are offered in a variety of sizes, providing a wide choice of layouts. The panels can be installed “tight” to an exposed deck to maximize the height of the space and in either long runs, grouped together, or placed individually based on acoustical need.

Cementitious wood fiber direct-attach ceiling panels combine an NRC up to 0.85 with a unique textured look and superior abuse resistance. The high-impact properties of these acoustical panels make them a good choice for heavy use interiors of commercial, institutional, recreational, and industrial buildings.

Wood fiber direct-attach ceiling panels are generally offered in their natural color, painted white, or custom colors. The panels can be painted in the field up to six times without reducing their acoustical properties. They can be attached to a variety of substrates including the underside of the exposed roof deck, the joists, and other commonly used support systems.

Case study
The acoustics in Temple University’s School of Architecture in Philadelphia were exhibiting excessively high reverberation times, affecting students’ ability to hear and understand their instructors. Acoustical testing by Metropolitan Acoustics of Philadelphia confirmed reverberation times were higher than recommended.

Consultant Graham Everhart of Metropolitan explains his team created models based off the testing to develop solutions.

“Our overall recommendation was to incorporate acoustically absorptive materials on the available surfaces,” he says, “and in most spaces, the most available surface was the ceiling, so we focused on that.”

The consultants then collaborated with Nelson, the Philadelphia architectural firm responsible for the retrofit project. “Considering the amount of hard surfaces, from an exposed metal deck and drywall walls to sealed concrete floors, it was easy to see why sound bounced around so quickly,” notes Scott Winger, AIA, technical director for Nelson.

To reduce reverberation time and improve speech intelligibility, the design team chose fiberglass direct-attach panels for the lecture halls and other presentation spaces and wood fiber direct-attach panels for the classrooms and studios. “Both panels perform in a similar manner acoustically, but we went with the wood fiber panels in the classrooms and studios because they were a little more rugged and better suited for these types of spaces,” Winger says.

Acoustical testing by Metropolitan following installation of the ceiling panels validated the choice of treatments. Reverberation time dropped an average of 56 percent in the eight spaces tested, including a 79 percent drop in one of the classrooms and a 64 percent drop in one of the studios.

“By installing the panels between the metal joists, we were able to maintain the look and feel of the exposed structure the university desired while mitigating the reverberation time, which it also desired,” Winger explains.

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Baffles
In addition to a variety of horizontal acoustical treatments, vertical treatments in the form of baffles and blades also help control noise in exposed structures. Like acoustical clouds and canopies, baffles and blades provide excellent sound absorption because sound is absorbed on both the front and back surfaces.

Baffles and blades are both suspended vertically to impart an upscale visual while providing substantial sound absorption. The most common baffles are made from wood fiber or fiberglass. Wood fiber baffles feature a coarse texture and are offered in a natural finish, painted white, or custom colors.

Fiberglass baffles are usually 0.6 x 1.2 m in size, and offered in numerous standard finishes, including woven fabrics and nylon sailcloths. Fabric-wrapped baffles are usually 50 mm (2 in.) thick while sailcloth baffles are 12.5 mm (1½ in.) thick. In addition to standard choices, custom options are also available to meet project needs. These include sizes and shapes up to 1.2 x 2.4 m (4 x 8 ft), thicknesses from 25 to 50 mm (1 to 2 in.), and square, stitched, beveled, mitered, or radiused edge details.

Suitable for either new construction or retrofit, one fiberglass baffle per 4 m² (40 sf), or 20 percent coverage, reduces reverberation time on average by approximately 50 percent. This makes them a good choice for use in exposed structure spaces such as auditoriums, gymnasiums, music rooms, and other open areas where sound absorption is needed.

In terms of installation, fabric-wrapped baffles are normally mounted with eyehooks, and sailcloth baffles with grommets. Installation is easy because all the components needed to suspend a baffle are normally contained in a hanging kit, including sleek, adjustable aircraft cable that imparts a clean look to the installation.

Blades
Blades offer another vertical acoustical solution for exposed structure spaces. Blades impart a much more linear visual than baffles while still providing excellent sound absorption.

The linear panels are offered in fiberglass, wood fiber, and metal versions. Metal panels must be perforated and include an acoustical fleece to obtain the desired acoustical performance. Fiberglass panels, which are the most common, are usually 50 mm (2 in.) thick and available in numerous standard sizes, shapes, and colors. Custom colors are also available. Standard panel profiles include rectangular, convex, concave, and curved for wave designs.

Panels are pre-assembled with metal hanging clips embedded in the top of each panel for easy installation from a standard suspension system. They can also be hung individually from the deck.

Blades are well suited for enhancing office, education, and retail spaces acoustically and aesthetically in either new construction or retrofit applications. When installed in a reverberant space, they can significantly reduce background noise and reverberation time, enhancing speech intelligibility.

Case study
Wacom, a high-tech manufacturer of interactive pen displays, recently moved its North American headquarters from Vancouver, Washington, to a new space in Portland, Oregon. As part of the relocation, company management desired an interior design that was far different from the traditional office space at its previous location and one that would entice prospective new employees.

To impart the industrial “feel” it desired, company management wanted a completely exposed concrete ceiling. However, because of all the hard surfaces in the space and the completely open work areas, the design team at SRM Architects in Portland knew some kind of acoustical treatment would be necessary.

To preserve the look of the exposed ceiling while providing acoustical control, the team chose blades.

“They proved to be the happy medium between a fully exposed ceiling and the acoustical performance we were looking for,” explains architect Stacie Fischer. “They are definitely one of the best solutions for retaining the open structure look while providing acoustical control,” she adds.

At Wacom, nearly 300 panels measuring 250 mm (10 in.) wide x 2388 mm (94 in.) long x 50 mm (2 in.) thick were installed throughout the space.

Fischer notes the Wacom open floor plan lent itself well to the use of blades.

“The blade layout appears to be randomly patterned, but the panels are actually clustered over workstation areas for better speech intelligibility.”

Blades were also installed in the private offices. “This is rather unusual, but we wanted to provide a level of speech privacy that these types of spaces require,” says Fisher.

Conclusion
Exposed structure spaces usually need some type of sound absorbing elements to control noise and reverberation. Figure 1 (page 53) documents the difference in reverberation time and overall sound level the installation of various acoustical ceiling treatments can make. Results for a continuous or “wall-to-wall” ceiling in the space are also included for comparative purposes.

Sean D. Browne is the principal scientist for Armstrong Ceiling & Wall Solutions in Lancaster, Pennsylvania, where he leads Armstrong’s acoustics program. A member of the Acoustical Society of America (ASA) and ASTM, Browne has engineering degrees from Florida State University and the University of Miami. He holds a patent for a power and signal distribution system for use in interior building spaces, and has been published in the journals of the International Symposium on Room Acoustics and ASA. He can be reached at sdbrowne@armstrongceilings.com[6].

Source URL: https://www.constructionspecifier.com/controlling-sound-in-exposed-structure-spaces/

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