Open-plenum spaces
Design trends often call for open-plenum or exposed structures, meaning those where there are no acoustical ceilings, and where building service elements such as ductwork and piping are directly overhead. Unless the sound control normally provided by the acoustical ceiling is replaced with an equivalent alternative system, there will be acoustical problems due to sound reflecting off the deck, resulting in excessive noise and reverberation.
Large spaces of this design will always need some type of sound-absorbing elements to control noise and reverberation. Additionally, when the exposed deck is less than 4.6 m (15 ft) high, reflections between cubicles can cause distractions for nearby occupants.
Noise issues related to open-plenum designs can be addressed in several ways, including acoustic elements attached close to the exposed deck or suspended down into the space. One such option is a discontinuous, high-NRC ceiling system designed specifically to provide excellent sound absorption while maintaining the look and feel of the exposed structure design.
These systems can be installed ‘tight’ to an exposed deck to maximize ceiling height, directly onto drywall, or suspended with wires. When suspended over only 20 percent of an area, systems that utilize panels with an NRC of 0.90 can reduce reverberation up to 50 percent.
Free-floating options
Noise issues in open-plenum spaces can also be addressed through the use of acoustical clouds, canopies, baffles, and blades—four types of ‘free-floating’ setups that add sound absorption while still allowing for the exposed look. All four options can absorb sound on two surfaces—both front and back in the case of clouds and canopies, and left and right sides in the case of baffles and blades. As a result, they can provide greater sound absorption than a continuous ceiling.
Acoustical ceiling clouds are available in a wide variety of standard sizes, ranging from 1.2 x 1.2 m to 3.3 x 4.3 m (4 x 4 ft to 14 x 14 ft). Depending on the panel, standard shapes range from squares, circles, and rectangles to hexagons, trapezoids, and convex or concave panels. Custom sizes and shapes are also available.
Acoustical clouds provide a type of interrupted ceiling plane when suspended above work areas. As such, they help control both reflections between cubicles and distant reverberation, reducing occupant annoyance and distractions. If the clouds are sufficiently large, ceiling panels with an NRC of 0.60 and above and a CAC of 30 and above can be very advantageous in collaboration areas to provide sound absorption and reduce noise intrusion.
Sound absorption
Acoustical canopies also reduce noise and reverberation in the space below them, but are much different in size and look compared to acoustical clouds. Acoustical canopies are smaller in size, ranging from 1 x 1 m to 1.2 x 2.4 m (3 x 3 ft to 4 x 8 ft). Visually, acoustical clouds are usually flat, while canopies are curved and can be installed as hills or valleys.
Baffles and blades are suspended vertically to impart an upscale visual while providing substantial sound absorption. Installation is easy because all the components needed to suspend a baffle or blade are contained in a hanging kit.
Whereas the sound absorption of a continuous ceiling is indicated by its NRC rating, the equivalent rating for ‘free-floating’ ceilings is the Sabin of absorption per element, such as a baffle or blade. The number of Sabin per element is approximately equal to the total surface area (in square meters) that is exposed to sound (either front and back or two sides), multiplied by the absorption coefficient of the material. Total Sabin absorption is measured according to ASTM C423, Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method.
Acoustics plus aesthetics
Regardless of the space, it is important to note aesthetics do not have to be compromised when using a high performance acoustical ceiling. For example, one of the more recent developments in aesthetic appeal is the introduction of high-performing acoustical ceiling panels with a smooth, drywall-like surface visual.
Another is the availability of acoustical ceiling systems that organize lighting fixtures, air diffusers, and sprinkler heads in a very narrow, technical ‘zone’ or strip to create a cleaner, more monolithic ceiling visual, eliminating the need for penetrations in the ceiling panels, and making them more aesthetically pleasing and easier to replace. Additional aesthetic options include panels with an edge detail that produces a 6.4-mm (¼-in.) reveal, minimizing visible grid and creating a ceiling plane that is more monolithic in appearance than ordinary suspended ceilings.
Panels are also available with a tegular or reveal edge to create a shadow line that helps camouflage the suspension system. In addition to their aesthetic appeal, tegular ceiling panels provide better sound blocking than square lay-in panels because there is less leakage at the interface between the panel and the grid.
