This CE Center article is no longer eligible for receiving credits.
People experience building interiors with all of their senses—sight, touch, smell, sometimes taste, and quite significantly, hearing. When those sensations are pleasant, supportive of health, or otherwise in line with what we expect, then a positive indoor environmental quality is achieved. When we experience negative sensations or subtle background conditions over time, then the indoor environmental quality is less desirable and may even be harmful to our health and welfare. All of these traits are particularly true when it comes to sound in buildings. Pleasant music, soft background sounds, or appropriate levels of quietness help define a space as different from one with distracting background noise or a lack of acoustical control. It has been well-documented by numerous sources that poor acoustics or exposure to unwanted noise in buildings negatively impacts the ability of people to concentrate, be productive, learn, or carry on meaningful conversations. Further, those exposed to these conditions over the long term can see a deterioration in their health related to physical and psychological degradation.
Photo courtesy of Turf Design
All of our senses are involved in the experience of a building, including our sense of hearing. Spaces that are designed for good acoustics produce better results for the people inside a building.
Based on all of the above, this course focuses on how the interior design of buildings can directly and proactively address acoustics and sound control. In particular, it looks at some specific strategies related to common interior surfaces, including walls and ceilings. Additionally, acoustical control at openings such as doors and operable walls is addressed to maintain acoustical separations. Overall, we explore different strategies and techniques to create positive indoor environments with desirable acoustical results.
Acoustics Overview
Sound is energy that radiates out from a source, just like heat and light are radiative energy. Understanding how to direct, restrict, or otherwise control sound is similar to how we do the same with other types of energy.
Images courtesy of NanaWall
When sound energy meets an obstacle (i.e., an interior surface), part is reflected, part is absorbed, and part is transmitted
In the case of interior acoustics, design strategies focus on what happens when sound waves travel into or through a space and meet a surface (i.e., ceiling, floor, wall, door, glazing, etc.). The particular effect that surface will have on the emitted sound waves will depend directly on the acoustic characteristics of the material encountered, but all will exhibit differing levels of the same three actions: In the case of interior acoustics, design strategies focus on what happens when sound waves travel into or through a space and meet a surface (i.e., ceiling, floor, wall, door, glazing, etc.). The particular effect that surface will have on the emitted sound waves will depend directly on the acoustic characteristics of the material encountered, but all will exhibit differing levels of the same three actions:
- Reflection: Some percentage of the sound will bounce off of the surface and be reflected back into the space. If this condition is severe, echoes are heard or sound levels seem to intensify.
- Absorption: Some materials (usually softer, porous ones) are very good at absorbing sound waves and dissipating the energy. In some situations, sound-absorptive materials are added to interior spaces to counteract reflection.
- Transmittance: Whatever sound is not reflected or absorbed is transmitted through the material or the assembly.
Image courtesy of NanaWall
STC ratings indicate how much sound is being prevented from transmission. The chart above provides some general guidance so designers can select the appropriate level for interior.
There are a number of different ways that each of these acoustical characteristics is measured. All are based on laboratory testing of materials and have become common and well-documented. One such measured test focuses on sound transmittance and measures how much sound passes through a given material or assembly. This test is referred to as a sound transmission class (STC) rating and is often provided by manufacturers as a means for designers to select appropriate materials to use in buildings. Essentially, the STC rating is a way to determine how much sound (measured in decibels) is reduced as it passes through a material or an assembly. The higher the STC rating, the more sound that does not transmit (i.e., more quiet). For most building conditions, an STC rating on the order of 40–45 is appropriate for most normal conditions, but ranges between 35 and 55 are also common.
Photos courtesy of PABCO Gypsum
Installing sound-reducing drywall can produce excellent acoustical control inside a building while relying only on standard drywall installation methods.
Acoustics in Framed Interior Partitions
Interior partitions are routinely constructed of metal or wood framing with gypsum board (drywall) on both sides. Gypsum panels are manufactured to meet various requirements as detailed by building codes, standards organizations, or other high-performance building guidelines. Most notable of these requirements is fire resistance, acoustic performance, mold-resistance, and abuse and impact resistance. Gypsum panels are tested per standard test methods to verify that they meet or exceed the criteria of given classifications.
With the increased focus on acoustics, human health, and worker productivity, higher STC ratings are more routinely specified in buildings. To meet these higher STC ratings, gypsum board partitions require enhancements beyond what conventional gypsum panels provide. Traditionally, these enhancements include adding sound insulation between the studs, using thicker or multiple layers of gypsum panels, or using resilient channels to decouple the drywall from the studs, all of which require additional time and extra cost. In the case of thicker or multiple layers of gypsum panels, the usable square footage of space is decreased and the increased depth of the partition can impact detail coordination, particularly around door openings and utility boxes.
Constrained Layer Damped (CLD) Gypsum Panels
As an alternative to conventional gypsum panels, there are some advanced products simply referred to as constrained layer damped (CLD) gypsum panels that offer excellent acoustic performance while integrating more easily with standard construction. Acoustic testing has been performed on a vast number of interior partitions using CLD panels to document the STC rating of the particular assembly. In many cases, the desired acoustic performance can be achieved with a single CLD layer without the need for multi-layered gypsum panels, resilient channels, or supplemental products. This also decreases the chance for improper installation that will negatively affect acoustic performance.
There are various CLD products available on the market, some more technologically advanced than others. These include a broad portfolio of products that can suit a variety of applications—from entry-level CLD panels for do-it-yourselfers to the highest-performing CLD panels ideal for high-end projects, such as recording studios, home and commercial theaters, and other sound rooms.
Variations of the Product
Just like other gypsum panels, CLD panels can be manufactured to meet or exceed other building code requirements, most importantly, the life-safety requirement of fire resistance. Some CLD panels have been tested in a number of different types of assemblies according to specific requirements to provide different fire-resistant-rated partitions that can be used to satisfy building code requirements
Some project applications require mold-resistant drywall panels. CLD panels can be manufactured to meet these requirements using special formulations for both the core and paper facings. Typically, mold-resistant CLD panels are available in thicknesses of ½ inch for use in non-fire-resistant-rated partitions and 5⁄8-inch Type X for use in fire-rated assemblies. For circumstances that warrant it, there is also sound-reducing drywall that can resist impact and abuse.
Ease of Installation
Field-installed products are often only as good as the quality of the installation. To help in this regard, CLD panels offer some intriguing advantages. First, there may be fewer layers of drywall to install, as STC ratings can be achieved with a single CLD panel instead of multiple layers of drywall. This saves installation time, reduces action steps, and helps control labor costs. Second, at least one manufacturer has developed panels that allow installers to easily score, snap, hang, and finish the drywall just like standard gypsum wallboard. With no paper or metal in the center of the panel, the drywall delivers high acoustic performance with improved workability to speed up installation time.
Related Products
To achieve the best performance in a partition, the joints and penetrations around and in between CLD panels also need to be addressed. Typically this means acoustical sealants and caulk/putty need to be properly applied to the perimeter of the wall and penetrations.
With the wide variety of building types and possible applications, it is recommended to work with a manufacturer and an acoustic consultant early in the design process to determine the best and most cost-effective products for any given project. It is best to work with manufacturers that bring a depth of technical knowledge, independent testing results, and a willingness to share the data with the design professionals who request it. These manufacturers also provide continuing education opportunities directly to firms or through professional associations
David E. Marsh, FASA, is the president and principal of Marsh/PMK International, a professional consulting firm specializing in acoustics and audiovisual system design. Referencing a recent corporate office project, he says, “The architect’s drawing notes called for a particular type of acoustical panel. We recommended a particular sound-reducing drywall manufacturer because of the research and development effort and money invested into the products, and the resulting lab test information available to consultants.”
Photos courtesy of NanaWall
Frameless operable glass walls, like the ones shown here, provide open, flexible integration of spaces when open and private, acoustically controlled spaces when closed.
People experience building interiors with all of their senses—sight, touch, smell, sometimes taste, and quite significantly, hearing. When those sensations are pleasant, supportive of health, or otherwise in line with what we expect, then a positive indoor environmental quality is achieved. When we experience negative sensations or subtle background conditions over time, then the indoor environmental quality is less desirable and may even be harmful to our health and welfare. All of these traits are particularly true when it comes to sound in buildings. Pleasant music, soft background sounds, or appropriate levels of quietness help define a space as different from one with distracting background noise or a lack of acoustical control. It has been well-documented by numerous sources that poor acoustics or exposure to unwanted noise in buildings negatively impacts the ability of people to concentrate, be productive, learn, or carry on meaningful conversations. Further, those exposed to these conditions over the long term can see a deterioration in their health related to physical and psychological degradation.
Photo courtesy of Turf Design
All of our senses are involved in the experience of a building, including our sense of hearing. Spaces that are designed for good acoustics produce better results for the people inside a building.
Based on all of the above, this course focuses on how the interior design of buildings can directly and proactively address acoustics and sound control. In particular, it looks at some specific strategies related to common interior surfaces, including walls and ceilings. Additionally, acoustical control at openings such as doors and operable walls is addressed to maintain acoustical separations. Overall, we explore different strategies and techniques to create positive indoor environments with desirable acoustical results.
Acoustics Overview
Sound is energy that radiates out from a source, just like heat and light are radiative energy. Understanding how to direct, restrict, or otherwise control sound is similar to how we do the same with other types of energy.
Images courtesy of NanaWall
When sound energy meets an obstacle (i.e., an interior surface), part is reflected, part is absorbed, and part is transmitted
In the case of interior acoustics, design strategies focus on what happens when sound waves travel into or through a space and meet a surface (i.e., ceiling, floor, wall, door, glazing, etc.). The particular effect that surface will have on the emitted sound waves will depend directly on the acoustic characteristics of the material encountered, but all will exhibit differing levels of the same three actions: In the case of interior acoustics, design strategies focus on what happens when sound waves travel into or through a space and meet a surface (i.e., ceiling, floor, wall, door, glazing, etc.). The particular effect that surface will have on the emitted sound waves will depend directly on the acoustic characteristics of the material encountered, but all will exhibit differing levels of the same three actions:
- Reflection: Some percentage of the sound will bounce off of the surface and be reflected back into the space. If this condition is severe, echoes are heard or sound levels seem to intensify.
- Absorption: Some materials (usually softer, porous ones) are very good at absorbing sound waves and dissipating the energy. In some situations, sound-absorptive materials are added to interior spaces to counteract reflection.
- Transmittance: Whatever sound is not reflected or absorbed is transmitted through the material or the assembly.
Image courtesy of NanaWall
STC ratings indicate how much sound is being prevented from transmission. The chart above provides some general guidance so designers can select the appropriate level for interior.
There are a number of different ways that each of these acoustical characteristics is measured. All are based on laboratory testing of materials and have become common and well-documented. One such measured test focuses on sound transmittance and measures how much sound passes through a given material or assembly. This test is referred to as a sound transmission class (STC) rating and is often provided by manufacturers as a means for designers to select appropriate materials to use in buildings. Essentially, the STC rating is a way to determine how much sound (measured in decibels) is reduced as it passes through a material or an assembly. The higher the STC rating, the more sound that does not transmit (i.e., more quiet). For most building conditions, an STC rating on the order of 40–45 is appropriate for most normal conditions, but ranges between 35 and 55 are also common.
Photos courtesy of PABCO Gypsum
Installing sound-reducing drywall can produce excellent acoustical control inside a building while relying only on standard drywall installation methods.
Acoustics in Framed Interior Partitions
Interior partitions are routinely constructed of metal or wood framing with gypsum board (drywall) on both sides. Gypsum panels are manufactured to meet various requirements as detailed by building codes, standards organizations, or other high-performance building guidelines. Most notable of these requirements is fire resistance, acoustic performance, mold-resistance, and abuse and impact resistance. Gypsum panels are tested per standard test methods to verify that they meet or exceed the criteria of given classifications.
With the increased focus on acoustics, human health, and worker productivity, higher STC ratings are more routinely specified in buildings. To meet these higher STC ratings, gypsum board partitions require enhancements beyond what conventional gypsum panels provide. Traditionally, these enhancements include adding sound insulation between the studs, using thicker or multiple layers of gypsum panels, or using resilient channels to decouple the drywall from the studs, all of which require additional time and extra cost. In the case of thicker or multiple layers of gypsum panels, the usable square footage of space is decreased and the increased depth of the partition can impact detail coordination, particularly around door openings and utility boxes.
Constrained Layer Damped (CLD) Gypsum Panels
As an alternative to conventional gypsum panels, there are some advanced products simply referred to as constrained layer damped (CLD) gypsum panels that offer excellent acoustic performance while integrating more easily with standard construction. Acoustic testing has been performed on a vast number of interior partitions using CLD panels to document the STC rating of the particular assembly. In many cases, the desired acoustic performance can be achieved with a single CLD layer without the need for multi-layered gypsum panels, resilient channels, or supplemental products. This also decreases the chance for improper installation that will negatively affect acoustic performance.
There are various CLD products available on the market, some more technologically advanced than others. These include a broad portfolio of products that can suit a variety of applications—from entry-level CLD panels for do-it-yourselfers to the highest-performing CLD panels ideal for high-end projects, such as recording studios, home and commercial theaters, and other sound rooms.
Variations of the Product
Just like other gypsum panels, CLD panels can be manufactured to meet or exceed other building code requirements, most importantly, the life-safety requirement of fire resistance. Some CLD panels have been tested in a number of different types of assemblies according to specific requirements to provide different fire-resistant-rated partitions that can be used to satisfy building code requirements
Some project applications require mold-resistant drywall panels. CLD panels can be manufactured to meet these requirements using special formulations for both the core and paper facings. Typically, mold-resistant CLD panels are available in thicknesses of ½ inch for use in non-fire-resistant-rated partitions and 5⁄8-inch Type X for use in fire-rated assemblies. For circumstances that warrant it, there is also sound-reducing drywall that can resist impact and abuse.
Ease of Installation
Field-installed products are often only as good as the quality of the installation. To help in this regard, CLD panels offer some intriguing advantages. First, there may be fewer layers of drywall to install, as STC ratings can be achieved with a single CLD panel instead of multiple layers of drywall. This saves installation time, reduces action steps, and helps control labor costs. Second, at least one manufacturer has developed panels that allow installers to easily score, snap, hang, and finish the drywall just like standard gypsum wallboard. With no paper or metal in the center of the panel, the drywall delivers high acoustic performance with improved workability to speed up installation time.
Related Products
To achieve the best performance in a partition, the joints and penetrations around and in between CLD panels also need to be addressed. Typically this means acoustical sealants and caulk/putty need to be properly applied to the perimeter of the wall and penetrations.
With the wide variety of building types and possible applications, it is recommended to work with a manufacturer and an acoustic consultant early in the design process to determine the best and most cost-effective products for any given project. It is best to work with manufacturers that bring a depth of technical knowledge, independent testing results, and a willingness to share the data with the design professionals who request it. These manufacturers also provide continuing education opportunities directly to firms or through professional associations
David E. Marsh, FASA, is the president and principal of Marsh/PMK International, a professional consulting firm specializing in acoustics and audiovisual system design. Referencing a recent corporate office project, he says, “The architect’s drawing notes called for a particular type of acoustical panel. We recommended a particular sound-reducing drywall manufacturer because of the research and development effort and money invested into the products, and the resulting lab test information available to consultants.”
Photos courtesy of NanaWall
Frameless operable glass walls, like the ones shown here, provide open, flexible integration of spaces when open and private, acoustically controlled spaces when closed.
Flexible Space, Acoustically Controlled
There are often design conditions with client requirements that can make acoustical performance more difficult if available options are not fully understood. A great example is the common request for building spaces to be more open and more flexible in the ways that they are used. Open, vibrant spaces can be great for large groups, but small meetings or individual workstations often need some acoustical separation. The design question then becomes how to provide both the desired openness and the needed acoustical control.
A popular solution to this seeming paradox is to use opening glass walls. This intriguing product type is comprised of individually framed glass panels that can be moved into either a closed or open position. The panels fold or slide along a track to open fully, permitting a once enclosed space to seamlessly reintegrate with those around it, allowing the space to be truly multifunctional. In the closed position, the glass panels can be specified to provide the appropriate level of acoustical barrier to create a more private, separated space. Floor-supported folding glass walls are able to achieve sound control up to impressive levels. This system combines sleek acoustically separated aluminum framing and specialized gasketing with sound-enhanced glass to achieve optimal performance with an STC range of 35–45.
Other all-glass opening walls are specifically engineered for enhanced acoustical separation and a minimalistic, frameless appearance. Such high-performance systems can provide better sound buffering than many fixed all-glass partitions. These systems have been independently tested and rated to a STC 36.
When selecting and specifying operable glass walls, it is important to consider not only the configuration and usability of the space but also the acoustical performance of the product. The higher-rated framed acoustical systems have been specifically engineered for interior spaces where acoustical privacy and ease of use are of utmost concerns, such as educational or work environments. The frameless versions offer flexible space management solutions for offices, banks, schools, or other building types, providing a design solution that goes beyond what a fixed glass wall provides. With no floor track required in many cases, these systems allow for uninterrupted transitions between interior spaces.
While some sound-control products require tools to crank and seal panels when closed, quality acoustic glass walls offer the user ease of operation. Some products are engineered with roller systems and acoustic seals that do not require additional efforts when closing. It is important to note that when the STC requirements of the system go up, so does the weight of the glass used within the panel. Therefore, it is best not to overload specification requirements when the environment may not require the highest acoustical values.
Other things to keep in mind are that product cost is determined by the level of acoustical privacy and the type of opening glass wall system selected. Hence, it is important to only specify the product and acoustically enhanced glass type that is needed for any given space. Finally, as with most construction, to achieve the desired acoustical control of any room, it is important that the sound-rated opening glass wall is properly installed. It also needs to be integrated into the space so that it is matched and surrounded with acoustically comparable ceiling, walls, and flooring.
Photos courtesy of AMBICO
Acoustic doors are available in a both wood and steel with a wide variety of appearance and performance options to suit any project.
Acoustical Doors and Frames
While walls and ceilings can be treated as continuous surfaces and addressed acoustically, intentional openings in those walls require particular attention. Doors in particular are needed for access, but if they are not also addressed acoustically, then unwanted sound transfer and noise will be unwelcome intruders. It is important to note that in most commercial building applications, this means addressing not only the operable door itself but also the door frame that couples the door with the wall.
Sometimes design professionals incorrectly assume that to make doors perform and achieve desired STC ratings, aesthetic beauty has to be sacrificed for performance. A review of the available options for acoustically enhanced doors and frames quickly reveals that this assumption is incorrect. Rather, a range of both wood and steel doors are now available that maintain the aesthetic options found on other commodity door types while still providing superior acoustic design and performance.
Interior doors between rooms and spaces often require other design attributes too, such as vision lites, fire ratings, and hardware configurations. Each of these needs to meet the functional requirements that they fulfill in a door and become part of its integrated design. However, each of these attributes will also directly impact acoustical performance in one way or another. Fortunately, there are manufacturers who welcome the challenge to provide wood and steel doors and frames that meet all of the aesthetic design attributes while still providing the needed acoustical performance. Often this is accomplished by careful selection of the materials used and optimizing them for performance and appearance. It also means paying close attention to the details of the interface between the door and the frame and the frame with the wall. In some cases, this includes the use of add-on gaskets and seals that inhibit the flow of sound, just as weather-stripping on exterior doors inhibits the flow of heat and drafts.
It is worth noting that doors and frames are acoustically tested according to the same standards as other building components. There are two common tests used by independent testing laboratories to determine acoustic performance. The first is ASTM E-90: Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements. The scope of this test method is intended to cover the laboratory measurement of airborne sound-transmission loss of building partitions, such as walls of all kinds, operable partitions, floor-ceiling assemblies, doors, windows, roofs, panels, and other space-dividing elements. The second is ASTM E413: Classification for Rating Sound Insulation. This classification covers methods of calculating single-number acoustical ratings (i.e., STC and related acoustical ratings) for laboratory and field measurements of sound attenuation in materials. Combined with ASTM E-90, this test is useful to determine how well an acoustic door reduces the amount of sound transfer between the two sides of the door.
The way to ensure that the best performance is achieved throughout a project is to specify acoustical doors and frames as a tested assembly from a single manufacturer. Otherwise the compatibility and seal between them may come into question without a clear means of who is responsible for resolving any issues that might arise. Manufacturers of such full door and frame assemblies can work with architects and designers to provide a full and varied range of options to meet the differing needs throughout a project. There is rarely a one-size-fits-all solution for doors and frames, but standardized systems can be used to create optimized assemblies with different STC ratings as needed for different openings. This is true for both wood and steel door assemblies that can be specified or selected based on all of the other design requirements and attributes being sought.
Following are some of the specific features of steel and wood acoustical doors.
Steel Doors
Steel doors and frames are widely used in commercial buildings of all types and can be readily specified to provide a full range of acoustic performance. The preferred products are a complete system with acoustic steel frames, perimeter and bottom seals, threshold, and astragal pairs that all work together to assure reliable, tested, STC ratings. Steel door assemblies that are 1¾ inches thick offer acoustic performance ratings from STC 33–53. In greater thicknesses, ratings of STC 54–59 are readily available. If higher ratings are needed, custom-engineered solutions can be pursued. Any of the doors can be provided with factory-installed acoustic glazing to allow vision while restricting sound. In addition to acoustical performance, steel doors can be provided with needed fire labels in single or double panels for most tested classifications covered by NFPA 80. The relatively lightweight panels combined with level swing seal systems allow for easy operation and compliance with accessibility standards required by codes and ANSI 117.1. From an appearance standpoint, they can be painted or finished in any common manner comparable to any other steel door product, thus providing all of the same design freedoms in addition to the specified performance.
Wood Doors
Acoustic wood doors with steel frame assemblies provide a broad range of STC ratings up to and including STC 56. The specific door and frame assemblies matter though. Wood doors that are 1¾ inches thick are rated up STC 50, while wood frames are available up to STC 45. Wood acoustic door and frame assemblies are also available to meet fire ratings up to 90 minutes. If vision lites are required, they can be factory glazed, including accompanying sidelites and transoms. With all of these performance attributes, remember that the beauty of wood can still be maintained and enhanced. Face veneers are available in virtually every wood species, cut, and grade. Stiles and rails are typically hardwood with vertical door edges to match the face. The factory finish can be a standard or custom stain or clear coat. If preferred for any reason, laminate face veneers are also available with hardwood edges. Doors can be Forest Stewardship Council certified to contribute to LEED or other green building rating systems.
Overall, steel and wood doors can meet all of the design and appearance requirements sought for a project while being specified to achieve the most appropriate acoustical rating.
Photos (from left): courtesy of Turf Design; © Eric Laignel Photography; courtesy of Turf Design
Acoustical treatments made from PET felt can be used as hanging baffles or integrated into ceilings in other ways to provide very good performance while also acting as notable design elements of an interior space.
Improving Sound Absorption on Ceilings and Walls
The interior design of commercial buildings often means that a variety of space types are created with a range of surface treatments on ceilings and walls. The shape of those spaces and the type of surface treatments all impact the acoustical performance of the space. Large spaces with highly reflective surfaces can create echoes, making it difficult to understand speech. Smaller spaces can suffer too from reflective surfaces with the sense of amplified noise as in a restaurant full of people. The solution to these sound issues is to use or add material to the walls and ceilings to reduce the reflected sound and increase the absorbed or dissipated sound.
Finding the most appropriate material to add to a space typically involves criteria based on three things: sustainability, performance, and design. Each of these is discussed further in the following sections.
Sustainable Materials
Any material used for building interiors needs to meet multiple criteria for durability, workability, fire resistance, and aesthetics. It has also become standard practice for many designers to incorporate sustainable materials into their projects. Toward all of these ends, one material has emerged as a popular and proven choice to create acoustical products from. Referred to as PET felt, this material is a form of polyester (like the clothing fabric) with a technical name of polyethylene terephthalate (PET). The most common use for PET felt in general is for it to be extruded or molded into plastic bottles and containers for packaging foods and beverages, personal care products, and many other consumer products. With a focus on sustainability though, PET felt is an alternative product that is routinely made from 60 percent pre-consumer recycled material. The manufacturing process creates felts that are flat but of varying thicknesses, sizes, colors, and textures. Some manufacturers make it a point to collect any felt waste and transform it to an energy source with lower key emissions than coal, thus avoiding the landfill. Additionally, they are actively researching ways to use waste to create new products. The combination of the material and manufacturing process has allowed some PET acoustical products to earn a Declare label as issued by the International Living Futures Institute, which developed the Living Building Challenge.
Acoustical Performance
PET felt products are very good at absorbing sound, making them a very effective solution for spaces that need acoustical improvement. While such products can contribute to the overall STC ratings of a wall or an assembly, they are more often used to help find the right combination of sound absorption versus reflection for a given space. This is essentially a matter of using several well-developed tools to balance the preferred acoustic characteristics within that space. These tools are known as the noise reduction coefficient (NRC) and Sabin measurements, both described as follows.
- Noise reduction coefficient (NRC): Individual materials can be formally tested according to ASTM C423: Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method. This standard is used to measure the rate of sound absorption of materials on a scale of zero to one. As such, NRC ratings of a material are commonly viewed as a percentage. For example, an NRC of 0.75 means that 75 percent of the sound energy that strikes a tested material is absorbed instead of being reflected or transmitted. Note, however, that since the test determines sound-absorption rates at four specific sound frequencies (250, 500, 1,000, and 2,000 Hz), the NRC rating number is actually an average of the results across those four frequencies that are generally in the range of human speech. Hence a material with an NRC of 0 can be presumed to reflect back all of the sound striking it within those four frequencies (i.e., not absorb any), while a material with an NRC of 1 is represented to absorb all of the sound that strikes it in this range. Therefore, NRC is useful for determining the sound-absorbing characteristics of materials in many general building applications, but not for special applications where sound at other frequencies needs to be addressed.
When PET felt products are tested, they generally achieve very high NRC ratings, including some that demonstrate more than 100 percent (i.e., NRC values greater than 1). These results will vary based on the circumstances of how it is used, the thickness and makeup of the PET felt, and variations between products.
- Sabin: When acoustic materials are placed to hang down in a space instead of on enclosing surface (walls, ceilings, etc.), a different sound measurement is needed. In this case, a Sabin is used as the measure of the total sound absorption provided by an individual sound absorber such as a ceiling baffle when installed within an architectural space. Absorption in Sabin is also measured according to ASTM C423. The number of Sabin per unit is approximately equal to the total surface area of the unit (in square feet) that is exposed to sound, multiplied by the measured absorption coefficient of the material. PET felt products are ideal for this type of application and commonly show test results with a very high absorption coefficient and Sabin ratings.
Based on the available testing data, acoustical products made from PET felt can be selected to reduce echoes and soften the sound in a space. To be the most effective, it is best to locate the products as close to the source of sound as possible. This usually means that applying it overhead (i.e., above where sounds are generated) is typically better than on walls that may be further from those sources. Nonetheless, wall-mounted products are usually designed to complement ceiling products and may be suitable on their own in some circumstances. PET felt products come in a range of types, including ceiling tiles, baffles, and clouds that are installed on supports to allow them to hang vertically or be installed horizontally as needed. Wall products are typically in the form of tiles that can be adhered to a substrate such as gypsum board or other materials.
Integrated Design
Adding acoustical material to a space means finding ways to balance the needed performance with the overall design scheme for that space. This includes finding the right textures, colors, and forms that can enhance or even help create an effective design. In this regard, it is worth noting that PET felt products are available in a wide range of options. Textures range from subtly smooth to more pronounced fabric-like appearances. Some products are intentionally three-dimensional, adding a sculpted or 3-D geometrical look to surfaces. In locations where the thickness is visible, there are choices ranging from thin 3-millimeter (0.11-inch) products up to 12 millimeters (0.47 inch), while some products use multiple layers to create thicker products on the order of more than 2 inches thick. Colors can be selected from a standard palette that includes whites, neutrals, bold, and accent colors in uniform or slightly variegated patterns. All of these attributes will vary by manufacturer and possibly between different product types or thicknesses, so it is always best to review the available options directly with the manufacturer first to confirm what desired products are available. Nonetheless, PET felt products can take on the role of being a functional product that disappears into the ceiling scape without competing against the architecture, or they can become an extension of architecture and make a bold visual statement.
In some cases, custom products may be available, with at least one manufacturer taking the approach that “custom is standard.” In this case, it takes on the challenge of fighting mediocre design by partnering with contractors, architects, clients, design firms, and fabricators. Using computerized parametric design principles, complex patterns or shapes are possible that can be created. Since this parametric approach actually simplifies the fabrication process, lead times can be shortened. At the same time, all products can be designed and fabricated to allow for easy installation, whether being used on ceilings or walls.
Overall, the integration of acoustical products into the interior spaces of a building can improve the general health and wellness of the people who use these spaces. By incorporating ceiling baffles, clouds, or wall tiles, the noise in a space is reduced. This can lead to less distractions, greater productivity and focus for completing tasks, and a more pleasant and enjoyable experience all around.
Photos (from left): © Brandon Stengel; courtesy of Turf Design
PET felt products offer great design flexibility with standard and custom possibilities for everything from bold geometric wall applications (left) to three-dimensional, undulating ceilings (right).
Conclusion
Architects and designers are well served when they take time in the design process to consider the acoustical needs of the building. Addressing the entire spectrum of sound control within individual rooms and spaces in a holistic or comprehensive manner will assure the best performance. By addressing the sound absorption, reflection, and transmission in a given room, the appropriate sound qualities can become part of a successful acoustic design. The multiple options available for materials and finishes allow architects and interior designers to retain control of the visual appearance of the walls, ceilings, and other surfaces. Further, by addressing the control of sound between spaces through walls, ceilings, floors, and specialty areas, each room can be appropriately shielded from background noise, unwanted sounds, and loss of privacy. Overall, this holistic, coordinated approach will yield a design that creates a very positive contribution to the total indoor environmental experience of the building.
