March 31, 2017
by Evan Troxel
Acoustics has an ever-increasing influence on modern commercial construction. There are guidelines stating how loud classrooms should be, how much noise workers can be exposed to, and even the level of privacy needed in sensitive spaces. Innovative building products and technology can help professionals meet new and changing standards, but these tools are only as good as the designs into which they are incorporated.
The most important factor in acoustics management for commercial projects is including acoustics in the early stages of the building design. Too often, the effects of this factor on a space are treated as an afterthought and considered too late. It is absolutely critical for architects and designers to plan, test, and execute acoustic design strategies in every phase from flooring products to ceiling systems, and space design to furniture selection.
The best acoustic solution for any built environment begins with good design practices and informed product selections that have a direct impact on sound transmission and absorption.Careful consideration of the acoustic goals for the building is essential, and will lead to the construction of healthier, less-stressful spaces.
Back to the basics
Sound energy can be generated through the air or through the building structure. Many noise sources, such as loudspeakers placed in contact with the floor or the movement of heavy objects (e.g. carts, desks, and chairs) across a floor can cause vibrations producing both airborne and structure-borne acoustic concerns.
Sound energy interacts with the surrounding floor, walls, and ceiling (Figure 1). At each boundary, portions of the sound energy will be reflected back into the room, absorbed by the contacted surface, or transmitted through to adjacent spaces. Surface materials and room construction determine how the sound energy will spread.
Common noise sources in buildings—other than inhabitants—tend to relate to HVAC, plumbing, electrical systems, or exterior factors. Strategies for addressing these sources depend on the space category and specific uses. Private areas, such as classrooms and conference rooms, have different needs than public spaces like restaurants, lobbies, and clinics.
In these cases, noise criteria (NC), balanced noise criteria (NCB), and room criteria (RC) must all be addressed to limit background noise and create environments conducive to specific uses and needs (Figure 2).
Addressing acoustics from the floor up
Floorcoverings and floor assemblies are becoming recognized as two important aspects of acoustic design. From hospitals to offices, gyms to libraries, innovative strategies can be used to prevent transmission of sound energy and create quieter spaces. In tandem with wall and ceiling solutions—specifically, noise-reducing gypsum and other products—flooring can increase acoustic results exponentially.
There are numerous metrics and standards for the assessment of different acoustic characteristics of building components. Thus, it is becoming increasingly important to specify and install products that can achieve specific goals and lead to quiet, stress-free environments in which people can work, heal, and learn.
To quantify the impact sound insulation capabilities of a floor assembly, impact insulation class (IIC) was created. This metric compares the sound levels in two adjacent rooms, one above the other. A contour-matching method is used to produce a single number representing the assembly’s effectiveness against impact noise. Also in use is the sound transmission class (STC)—a single number to quantify transmission capabilities, it is employed across several applications, including flooring, walls, and ceilings.
There are two main differences between IIC and STC. First, the noise source utilized in IIC measurements is a tapping machine coming into contact with the floor of the upper space. In STC, the machine is placed directly against the wall. Second, the surface of the flooring can play an important role in reducing impact noise, but less so with sound transmission. Carpet and padding, including low- or medium-pile, can reduce the ‘clacking’ of impact sources on a building structure, significantly increasing IIC ratings—especially in wood construction.
A floor construction with carpet and padding may have a high IIC rating, but demonstrate a low STC against airborne noise. When the IIC of a building construction increases by 10 (when, for example, a floorcovering is added), the sound level is perceived to be half of what it was previously. For the human ear to notice any difference, the sound level must change by at least 3 dBa.
“It’s essential to address acoustical needs within any space prior to specifying materials,” says James Johnson, a flooring expert. “Flooring is one material that can greatly contribute to an ideal indoor environment—especially as it relates to transmission of impact noise.”
Acoustic performance in specific spaces
It is important to note not all flooring product applications are the same.
In hospitals and doctors’ offices, the most prevalent surfaces are hard, sealed floors—likely because this flooring type can fulfill sector-specific needs.
A recent study by Health Care Without Harm showed in these settings, “the four priority issues that went into flooring decisions for all of the user types were cleanability, aesthetics, durability, and initial cost.” (This quotation is taken from the 2010 publication Sustainable Resilient Flooring Choices for Hospitals: Perceptions and Experiences of Users, Specifiers, and Installers by Jennifer DuBose and Amaya Labrador. A summary is available here.)
Hospital facilities involve massive structural elements, which can naturally lead to low sound transmission between levels. STC ratings also depend on the type of structural system used and its rigidity and mass.
The issue arising with hard floors is the propagation of structure-borne impact noise, particularly from carts and footfall. Such noise has been found to affect patient health, as it imposes additional stress. Consequently, carpet is becoming more prevalent in high-traffic areas of hospitals, like hallways and waiting rooms.
As with the healthcare industry, most flooring found in schools possesses hard, resilient surfaces that enhance functionality and durability. However, carpeting can be installed in specific spaces to reduce impact noise from sources such as chairs scraping against floors. Classrooms, for example, generally require lower background noise levels and lower reverberation times to ensure students can clearly hear instructors. Absorptive materials with high noise reduction coefficients (NRCs) are effective when placed on the ceiling or upper wall.
“Most classroom settings require complete auditory solutions that pertain to flooring as well as the walls and ceiling assemblies,” says Robert Marshall, an expert in ceilings. “There are high-performance ceiling panels available, such as fine-fissured mineral fiber solutions, that not only meet rigorous acoustical standards, but exceed them within the ceiling category alone.”
Carpet, walls, ceiling tiles, and partitions can be installed to address unwanted sound. In an office, the main distracters are ‘people sounds’ like phone conversations, throat clearing, and vacuum cleaners, but can include anything that could distract a listener.
Walls are especially critical in open-concept offices, where meeting rooms are necessary to block and/or absorb unwanted noise. Walls serve as the enclosure of a space—thus, the installation of acoustically rated drywall products specifically designed to provide mass to the system can disguise unwanted noise and increase levels of privacy when needed (Figure 3).
“Advanced drywall products with inner layers of viscoelastic polymer help dampen vibrations by creating a shock-like absorber within the structure of the wall. This type of ‘constrained layer damping’ performs well acoustically over an extended range of frequencies, resulting in increased STC ratings for the systems,” says Lucas Hamilton, a gypsum wallboard expert.
Regular, predictable background sounds, like an HVAC system, are easier to block out than disruptive sounds, like conversation over a cubicle wall.
“However, HVAC system sounds can also be addressed with rotary duct liner insulation,” says Hamilton. “A key benefit of insulating a duct on the inside is that the insulation provides noise reduction, in addition to maintaining the temperature of conditioned air that passes through it. Furthermore, when ceiling tiles, which are highly absorptive, are used in conjunction with other highly absorptive products like flooring, insulation, drywall and partitions, they can play an essential role in office acoustics.”
However, mechanical system sounds can also be addressed with rotary duct liner insulation. This not only moderates the temperature of the air passing through the HVAC system, but also reduces noise—particularly effective when used in conjunction with flooring, drywall, partitions, and other types of insulation.
As employers continue to renovate and build open office spaces, employees are voicing concerns about their abilities to work productively in what they anticipate will be a noisier, more distracting workplace. The overwhelming complaint about open-plan office design is the lack of acoustic privacy. (For more information, consult the Springer Handbook of Acoustics, edited by Thomas Rossing and published in 2014.)
Some settings within this environment may call for only visual privacy, but others require both visual and total speech privacy, while end-users in the same space might need normal speech privacy (in which conversations in adjacent areas can be understood, but do not detract from concentration). Proper acoustic design, including furnishings, partitions, and partial walls, can help address these needs while averting serious issues down the line.
These questions might seem trivial at first, but common concerns such as privacy and distractions have been proven to affect productivity, reducing worker output and ultimately the bottom line for employers. Design firm Gensler estimates three out of every four American workers are struggling to work effectively in ineffective workplaces. (More on the survey from which Gensler derived this statistic can be found here.) In fact, distractions in the open-office environment have forced workers to exhaust themselves with increased efforts to concentrate, abandon current tasks to deal with interruptions, and take as much as 15 minutes to regain their train of thought and get back into the flow of complex tasks.
“Designers have to address several factors when it comes to open, collaborative office concepts,” says Marshall. “The first thing typically addressed is the ceiling, as it’s an excellent sound absorber. In order to effectively measure how well the ceiling will absorb sound, it’s important to evaluate the articulation class (AC). This is a rating system for speech privacy performance within an open-plan environment.”
Marshall also states partitions can be used to provide visual privacy as well as blocking sound.
“Open collaborative spaces increase airborne noise and visual distractions,” agrees Johnson. “To address these challenges, designers can take a holistic approach that accommodates acoustical ceiling tiles and partitions within the space. The integration of both reduces airborne sound transmission and visual disruptions.”
In a healthcare setting, for example, a rolling hospital bed may be heard in the room or floor below. Implementing acoustical ceiling tiles and sound masking will reduce the perceived transmission of that heavy load. These systems work together to efficiently mitigate sound, with no single system working best independently.
Concern for privacy has turned much more serious in recent decades, due to the passing of privacy-protection laws by the federal government. Current U.S. law requires the transfer of health records, for example, to conform with privacy requirements passed in the 1996 Health Insurance Portability and Accounting Act. This encompasses privacy for digital transfer of health records between healthcare providers, and presumably aural privacy as well.
Many universities and other higher-education facilities must also provide administrators and faculty with private spaces where they can meet with students to discuss grades, disciplinary action, and other personal or sensitive information.
Benefits of designing with sound-absorbing materials
An example of a space utilizing sound-absorbing materials to improve acoustic conditions is global engineering company AECOM’s new offices in Pretoria, South Africa. Built in 2014, the offices include several acoustical ceiling solutions, with the most impressive part located in the atrium. Though this space was originally just an entrance, AECOM decided it could be used as a dining and lounge area as well.
Given this particular spot would be utilized for informal meetings, training, and presentations, high noise levels were expected. The design goal was to explore the effects of an explosion and to translate it both visually and practically.
The result is a complex, visually stunning installation of acoustic ceiling tiles and baffles in a combination of standard and custom sizes. The long reverberation time originally present in this space has been reduced dramatically, with the ceiling solution making a substantial difference to noise levels, greatly improving overall speech clarity and intelligibility.
Using auralization tools to ‘hear’ a space before it is built
One way that architects and designers can test acoustics for commercial spaces such as offices is to use new auralization tools. Just as sketches and 3D renderings are used to visualize an unbuilt project’s aesthetics, new tools can help specifiers design with acoustic modeling in mind.
Sound modeling tools can enable the specifier to hear how ceiling design, materials, and product specifications can affect the acoustics of a space. One example, referred to as a ‘Listening Lounge,’ tests the human listening experience within a defined area before that area is built, allowing specifiers to better understand the materials needed to provide an acoustically sound space. (The author would also like to thank Stan Gatland [CertainTeed] for his various contributions on the Listening Lounge concept.) Participants can click on different solutions and evaluate their actual perception of the difference each material makes.
“According to Amplitude Research Inc., 65 percent of workers are distracted by too much noise at work,” says building sciences expert Stan Gatland. “For someone sitting at a work station within an open-plan setting, general office conversations can create a noticeable distraction.”
Designers can use the Listening Lounge to preview the impact of interior finishes, audio systems, sound isolation, and an electronic speech privacy systems (i.e. sound masking), while room acoustics can be adjusted to demonstrate the impact of various NRC and ceiling attenuation class (CAC) levels. These differing acoustic metrics can be applied not only to the open-office model, but also to conference rooms, large cafeterias, and auditoriums hosting public speakers.
(The author would like to thank James Johnson [Armstrong Flooring], Robert Marshall, P.Eng., BDS, LEED AP [CertainTeed Ceilings], and Lucas Hamilton [CertainTeed Gypsum] for their contributions to this article.)
Evan Troxel is associate and senior project designer at HMC Architects in Ontario, California. He specializes in public works projects including higher education facilities, pre-K–12 schools, and civic and other institutional projects. Troxel also serves as a co-host of Archispeak, a podcast about all things architecture, where he shares his passion for and experiences in the architectural profession. He can be reached at email@example.com.
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