Key Terminology for Understanding Sound and Sound Ratings

Sound is measured in two ways: its loudness is measured in decibels (dB), and its frequency is measured in hertz (Hz). Combined, these two measurements are at the foundation of how sound management systems operate. But it’s a lot more complicated than just decibels and hertz, especially when it comes to specifying architectural materials that manage sound and noise within spaces.

Noise-reduction coefficient (NRC) is the measurement of how well a material absorbs sound, usually sounds in the range of normal speech frequencies. On products, NRC is usually measured at frequency octave ranges of 250, 500, 1000, and 2000 Hz, and those measurements identify how much a product will make a space quieter at that frequency ranges. Large spaces where sounds and noises are generated, such as gymnasiums, sports arenas, restaurants, or performance halls, will require a higher NRC on walls and ceilings to control the noise.

Sound transmission class (STC), on the other hand, measures how well a surface blocks sound from going through it, or how well a product keeps sounds from escaping a room. Spaces such as medical clinics, hospital rooms, or office conference rooms where private or sensitive information may be discussed will benefit from walls designed with high-STC products, as covered by the ASTM E90 standard.

Reverberation, or how long a sound continues to reflect off of hard surfaces within a space, is measured in reverberation time (RT). RT is measured as the time in seconds that it takes for the sound level to decay by 60 dB. From a practical standpoint, a long RT is responsible for situations where communication is garbled and difficult for listeners to understand, also known as speech intelligibility. Some spaces, such as classrooms, benefit from very short RTs (less than 0.6 seconds) in order to emphasize clarity and speech intelligibility, while others, such as performance halls and theaters, benefit from RTs of greater than 1.2 to help the sound fill the space.

Articulation class (AC) measures the attenuation, or how much sound energy is lost, of reflected sounds, such as speech over the top of wall partitions or furniture, and is measured according to ASTM E1110 and E1111. For example, high-performance AC is important in office areas that rely on cubicles. AC ceiling systems rated 150 or less are considered low performance, where systems that are rated 180 or greater are considered high performance.

A final acoustic performance measure is the Privacy Index (PI), which rates how well speech can be heard in and through architectural spaces, especially spaces such as hospitals and offices. Key PI levels are generally accepted to be 95 percent or higher for confidential speech privacy, 80 to 95 percent classifies as “nonintrusive” privacy, and anything below is accepted as poor or not private.

Acoustic Solutions for Sound Management and Aesthetics

In today’s market, there is a wide range of high-performance acoustic design solutions that address an equally wide range of acoustic challenges. We will cover different types, styles, and attributes of acoustic solutions, including shapes, sizes, and finishes, as well as the various materials and material properties of different acoustic solutions. This includes multilayered gypsum panels and textured sprays to glass, stainless steel, wood and steel doors with steel frames, and different types of ceiling tiles and baffles.

In addition to the practical aspects of new acoustic designs, the different products offer architects and designers a world of creative options for aesthetic flexibility. This flexibility extends from traditional ceiling and wall solutions to doors and doorframes, with an array of colors, shapes, sizes, and patterns available—all delivering high-performance acoustic control that improves the comfort and beauty of the space. In addition to the flexible products, recent advances in modular design offer almost unlimited possibilities for layout to best fit the required space. Other designs incorporate daylighting quality with their sound- and noise-control solutions, and many are fire rated to provide added safety within the space. We’ll take a look at each one now.

Stone Wool Ceiling Panels

Sound-absorbing ceiling systems can optimize acoustics and add to the comfort and aesthetic design of an indoor space. For projects where a creative, flexible look is desired, stone wool ceiling panels installed on specialty metal ceiling panel suspension systems can be a great choice and address some of the newer, stricter requirements in acoustic standards. As Acoustics Specialist Gary Madaras, Ph.D., of Rockfon notes, “A lot has changed in the acoustics realm recently, especially in regards to the stringency of both sound-absorption and sound-blocking requirements in the standards. Ceilings have to provide high sound absorption to meet shorter reverberation times, and full-height walls and heavy slabs are needed to provide privacy and prevent noise intrusion.”

For example, optimized acoustics in commercial interiors typically include high-performing sound absorption overhead, which helps protect materials from dirt and damage. Regardless of the interior, acoustic ceiling systems should not be seen as a way to compensate for the poor design of other building elements, such as floors, walls, and mechanical systems. A well-designed interior should meet the requirements for privacy between enclosed rooms, and mechanical systems should meet maximum permissible background noise levels: acoustic ceilings can be removed and replaced with different types of sound absorption.

Industry literature shows that an absorption performance level of NRC 0.90 or higher is required in workplaces and patient-care areas of health-care facilities. This minimum performance level has been adopted for open offices by some standards, guidelines, and building rating systems, such as The WELL Building Standard v1 and the U.S. General Services Administration’s (GSA) Facilities Standards for the Public Building Service (P100). The Center for Health Design establishes installing high-performance sound-absorbing ceiling tiles as a priority design recommendation based on its impact on safety, quality, and cost.

Not all spaces require this high level of sound absorption. Most ceiling manufactures provide multiple options within standard performance levels. The most important factor to remember when it comes to acoustic ceilings is that they are for sound absorption within spaces and too lightweight and porous to be effective at blocking sound.

Cementitious Wood Fiber Ceiling and Wall Panels

Acoustic ceiling and wall panels can be made from many different materials, each of which provide certain properties that can benefit an indoor environment. Cementitious wood-fiber offers an acoustical high-performance, ecofriendly option that is also cost-effective and provides additional thermal insulation to the space. As a material, cementitious wood-fiber is remarkably simple, with three key ingredients: managed source wood fibers, cement, and water. The finished panels are durable, fire rated, and low VOC, making them a safe and healthy option for interiors. Panels are also versatile in terms of size, shape, mounting options, and even paint options, which makes them easy to specify, and their thin design makes them easy to install.

Photo courtesy Acoustical Surfaces

Shown are ceiling and wall cementitious wood fiber panels.

As an acoustic solution, cementitious wood fiber panels provide designers with an aesthetically creative option that typically has a consistent finish and color as well as consistent thickness, square corners, and low-dust square panels. These panels are designed to effectively manage sound in larger spaces where noise is typically a challenge, such as in schools or civic centers—for example, in gymnasiums and classrooms, auditoriums, or music practice and band rooms. They are also an excellent option for commercial venues such as restaurants and bars, convention centers, and even “extreme noise” environments such as manufacturing and industrial facilities, among many other noisy, high-traffic spaces.

Sound-Reducing Drywall

Sound-reducing laminated gypsum drywall is an affordable, easy-to-install acoustic solution. The material can replace any standard drywall in either walls or ceilings, and it can use standard construction techniques to achieve high STCs. This is beneficial because it avoids the common issues of decoupling walls or difficult installation that contractors often face with some of the noise-control solutions; such problems tend to mean that the desired result is not achieved.

Sound-reducing gypsum panels can be cut and mounted like any other drywall panel, with the only real difference being that these panels are “internally damped” with constrained layer-damping layers inside. Different performance grades are available, including a standard ^5/8-inch type X panel, which is the same size as standard drywall.

The combination of high performance, easy installation, and overall low cost works well for projects where time and budget are of key importance. As noted by Matthew Boersma of HerreroBOLDT Partners, “After completing our analysis, it was clear that sound-damping gypsum drywall would be the best solution to achieve the required STC performance, at the lowest cost, for the Cathedral Hill district campus. Additionally, using sound-damping gypsum drywall standardizes the wall dimension and reduces variability for other in-wall systems like doorframes and receptacle outlets.”

Acoustic Plasters and Perforated Gypsum Board

According to Howie Podolsky, general manager of Pyrok, in many interior spaces, “it is necessary to address mechanical system noise, sound transmission, impact noise, and sound-absorption issues. Too often, all four of these critical acoustic issues are not addressed.” Sound-absorption issues can be addressed with perforated gypsum boards with different perforation patterns that can be joint-taped to create high-performance, durable acoustic solutions or acoustic sprays. Two such sprays available are seamless, durable sound-absorbing wall and ceiling treatments constructed from hand-applied smooth and textured sprays. These sprays, made with a special sound-absorbing substrate comprised of recycled post-consumer glass, offer a sustainable, durable, safe, and healthy acoustic option that can have almost zero VOC content. Designers can use this product to achieve the look of a seamless gypsum board but with acoustic properties. The material can be used in whatever way gypsum boards are used, including curved surfaces and compound curves, with the advantage that no gypsum board substrate is required. Moreover, such products can be painted without losing any sound-absorbing qualities.

Another option is an acoustical plaster spray made with portland cement, and that can be applied to unpainted concrete masonry, galvanized metal deck, and structural steel. These plaster sprays can be used wherever a designer might otherwise use a decorative plaster finish, but they also absorb sound, are durable, and require very little maintenance. This combination of attributes provides architects and designers with aesthetic flexibility whether the interior is contemporary, traditional, or even a historical restoration. One benefit of the plaster spray is that it can be applied in different thicknesses depending on the desired acoustical result.

Acoustic Drywall Ceiling and Wall Systems

One way that designers can balance their aesthetic vision of a space with eventual occupant comfort is to include acoustics as a critical requirement very early in the project’s design process. Acoustic needs—and eventual solutions—should be considered a key design decision, just as important as materials, performance, and aesthetics. By addressing the issue of acoustics early in the process, designers can better plan for materials and products that best suit their budget and deadline needs as well.

For architects and designers seeking modern, monolithic ceilings, acoustics can be a genuine challenge. Sounds can easily bounce off of the surfaces, reverberating and echoing, thus making listening difficult. New advances in acoustical drywall ceilings, however, offer systems that can be sprayed to have a monolithic look, all while costing less and being far easier to install than acoustical plaster. These high-performance solutions can also provide high light-reflective finishes that can enhance interior lighting, thus reducing energy use.

Acoustic Luminaire and Baffle Systems

Acoustic linear luminaire and baffle systems combine noise control with lighting control. Linear luminaires, for example, can provide a modern look with ecofriendly and sound-absorbing housings. They are offered with direct, indirect, or both direct and indirect light distributions, thus ensuring not only improved acoustics within a space but also optimal illumination levels. With the integration of lighting controls, these acoustical lighting products can also reduce energy costs. Unlit acoustic baffles provide an aesthetic match to the lit baffles, adding to the overall flexibility to meet a project’s budget, aesthetic, lighting, and acoustic needs.

Acoustic luminaires and baffles can be used to create unique, project-specific aesthetics in conference rooms, offices, reception areas, and other open commercial spaces. The thin profiles of the acoustic baffles maximize illumination and minimize shadows. In addition to standard linear acoustic baffles, acoustic pendants can be used in larger interior spaces where noise may be a problem, such as in airport concourses, large lobbies and reception areas, or conference rooms and open workspaces. Acoustic pendants can be used in conjunction with lighting systems to create bright, comfortable, healthy, and coordinated interior spaces.

Folding and Opening Glass Walls

Glass walls can serve as excellent acoustic barriers when they are closed; however, such walls have traditionally been installed as permanent fixtures to a space. New designs in floor-supported folding glass walls, however, combine the modern aesthetic of acoustically separated aluminum framing and specialized gasketing with sound-enhanced glass. These new high-performing systems can achieve STC levels ranging from STC 35 to 45. Aside from the versatility of these glass walls, they provide educational and interior spaces with easy-to-create private rooms. The floor-supported steel framing, for example, makes opening and closing the walls easy for anyone to do.

While not all spaces benefit from a folding wall, another option is an all-glass opening wall that is engineered specifically for enhanced acoustical separation. Opening glass walls can turn larger spaces into on-demand smaller spaces, all while keeping the space visually open. Such walls can perform better than many all-glass fixed partitions, with STC ratings around 36 and outdoor-indoor transmissions class (OITC) of 30. All-glass opening walls can change the noisy nature of office spaces, banks, and schools with uninterrupted transitions between interior spaces.

Acoustic Door Assembly Products

As noted earlier, a space that requires high-performance acoustic management also needs to have carefully specified doors and doorframes. Both are critical elements in an acoustic space in that they not only block sound but also play a key role in fire safety. Two design solutions include acoustic steel and acoustic wood doors with steel frames.

Acoustic soundproof wood doors with steel-frame assemblies can provide an excellent solution to noise issues in buildings such as schools and health-care environments, where noisy corridors may distract people within spaces like classrooms, exam rooms, or patient-care rooms. In addition to the aesthetics of wood-faced doors, these doors and assemblies can provide the broadest range of STC ratings in the industry, all tested with ASTM E-90 and E-413, and fire rated up to 90 minutes. Heavy-gauge, pressed-steel frames and engineered perimeter- and bottom-seal frames help reduce unwanted noise.