Innovations in Acoustical Ceilings for Today’s Flexible Interiors

Total acoustical quality for offices, healthcare facilities, and classrooms

Understanding how to design for acoustics in flexible interiors takes on new importance as traditional recommendations are not so compatible with current design trends. Architects are challenged with designing spaces that have multiple functions. Now the science behind the ceiling is able to provide both high sound absorption and sound blocking in the same panel.

This article demonstrates the importance of choosing ceilings having both good sound absorption performance as rated by the noise reduction coefficient (NRC), along with good sound blocking performance as rated by the ceiling attenuation class (CAC) for simple ceiling options that can help provide the right acoustical solution for the design.

Acoustics 101

Noise is unwanted sound. It comes from:

► Overheard speech from private conversations

► Sounds from adjacent spaces

► Reverberation from hard indoor surfaces

► Building mechanical systems

► Traffic and environmental sources

Noise problems can be improved with a choice of enhanced ceiling materials that both absorb and block unwanted sound. In this section, we'll discuss the problems with poor acoustic design and performance, and how that performance is evaluated.

The Gensler 2013 U.S. Workplace Survey¹ examines “What Factors Drive Workplace Performance?” The company commissioned a nationwide survey of 2,035 professionals to examine the design factors that create an effective workplace.

The results showed that U.S. workers are struggling to work effectively and overall work performance has dropped 6 percent since the last Gensler study in 2008.

As the study reaffirmed, effective workplaces have a balance between focused work and collaboration. Since 2008, the time spent in focused work has increased 13 percent, while time spent collaborating has decreased 20 percent. In the end, choice drives performance and innovation. Giving employees a choice of when and where to work increases their performance.

The solution to workplace performance is in providing effective focus space. The study says: “Design factors that influence the ability to focus most significantly include the functionality of primary space, design look and feel of primary space, and effective noise management.”

To be most effective, workers need to both focus and collaborate, two very different activities that often happen in the same space, with unwanted noise playing a big part in the functionality, or lack of functionality, of the space.

In the Danish-American Acoustic Satisfaction Study², researchers at Technical University of Denmark and the Center for the Built Environment (CBE) at the University of California Berkeley analyzed acoustic satisfaction of 23,450 survey respondents from 142 buildings on acoustic satisfaction.

The conclusions and implications of the study may be just as alarming to bosses as it is informative to architects and designers:

► Office workers are significantly more dissatisfied with the lack of speech privacy than with the level of noise.

► More than 50 percent of cubicle occupants think poor acoustics interfere with their ability to get their job done.

► Thirty percent of those in private offices say poor acoustics interfere with their ability to work.

► In indoor environmental quality, poor acoustics causes the most dissatisfaction.

► More focus on speech privacy and noise is needed.

The important factor to remember is that buildings are for people. The goal should be to provide a space that is healthy and productive for the occupants, as well as energy efficient and sustainable.

Towards addressing that goal, acoustic comfort means an acoustic environment that provides speech intelligibility for communications and safety, speech privacy for confidentiality, low distractions and annoyance, and good sound quality for recorded and A/V programs.

It's fair to say that current approaches to building design and construction are not meeting the occupants' indoor environmental quality and acoustic needs.

Poor Acoustics Not Adequately Understood

Acoustical design is certainly part of the solution. According to studies by the CBE³, “noise is probably the most prevalent annoyance source in offices, and that can lead to increased stress for occupants.”

The lack of speech privacy, the CBE says, is the most important factor.

However, the CBE states, “Acoustics in most cases do not receive the level of design attention as thermal, ventilation and other architectural and engineering considerations. The causes and consequences of poor acoustical performance are perhaps not adequately understood by designers and building owners.”

In the past, ceilings typically offered either good sound absorption (noise reduction coefficient, NRC) performance to control reverberation and decrease unwanted sound levels, or good ceiling attenuation (CAC) to blocking unwanted sound intrusion into spaces. Now, there are ceilings with combined high NRC and high CAC performance for an ideal combination of acoustical control in one panel.

Because workers spend more time focusing and less time collaborating than in the past, acoustic design becomes even more important to solve noise and speech privacy problems.

It helps to understand a few principles and the terminology used in the acoustic design.

Measures Relating to Sound Within a Space

Noise Reduction Coefficient (NRC)— A measure for rating the overall sound absorption performance of a material when used in an enclosed architectural space such as an office, where sound is being reflected at many angles of incidence.

Specifically, it is the 4 frequency averaged absorption coefficients @ 250, 500, 1000 and 2000 Hz, rounded to the nearest 0.05. A material with NRC < 0.50 (which means it absorbs less than 50 percent of the sound energy that strikes it) is a poor absorber, and NRC > 0.70 (which means it absorbs more than 70 percent of the sound energy that strikes it) is a very good absorber.

Reverberation—The buildup of sound within an architectural space, such as a room, as a result of repeated sound reflections at the surfaces of the room. Exposed structure—those spaces having no ceiling but with exposed building service—will often have noise problems. Sound reflecting off the deck above creates excessive reverberation such that large spaces require sound absorption to reduce distracting noise. There are acoustical treatments available to address these types of spaces.

Reverberation Time (RT)—A measure for rating the quality of the sound environment within an architectural space, and its appropriateness for various uses. Specifically, the reverberation time is the time it takes for reflected sound within a space to decrease by 60 dB after the sound was made. Typically, an RT < 1 second is good for speech intelligibility, while an RT > 2.5 seconds is good for symphony music.

Measure Relating to Sound Attenuation (Transfer) Between Open Plan Spaces

Articulation Class (AC)—A measure for rating the speech privacy performance of a ceiling in an open plan environment where sound is reflected off the ceiling between two adjacent spaces divided by partial-height furniture panels. A ceiling system with AC ≤ 150 is low performance, while one with AC ≥ 180 is high performance.

Measures Relating to Sound Blocking (Transfer) Between Closed Spaces

Ceiling Attenuation Class (CAC)—A measure for rating the performance of a ceiling system as a barrier to airborne sound transmission through a common plenum between adjacent closed spaces such as offices. A ceiling system with a CAC ≤ 25 is considered low performance, whereas one with CAC ≥ 35 is high performance. CAC is measured according to ASTM E1414.

Sound Transmission Class (STC)—STC is the wall equivalent of CAC and is a measure for rating the performance of a wall system as a barrier to airborne sound transmission between closed spaces such as closed offices, corridors, and conference rooms, and even in open offices with furniture and dividers, etc. An STC ≤ 35 is considered low performance, while an STC ≥ 55 is considered high performance. STC is measured according to ASTM E90.

Articulation Index (AI)—The AI is a measure of the intelligibility of speech in the presence of background noise, and is related to the signal-to-noise ratio, S/N. The AI ranges from 1.0 which means that the speech is highly intelligible, to 0.0 meaning that speech cannot be understood. Speech Privacy (PI) is calculated from the AI to indicate the level of speech privacy according to the following: PI = (1-AI) * 100%, and is generally rated as PI > 95% is confidential, and PI = 80 to 95% is non-intrusive.

These measurements will inform architects as they contemplate and calculate the acoustic qualities needed for various environments. We'll begin with offices.

Acoustic Solutions in Offices

Traditional workplaces can be generally described as a combination of open plan and closed plan design. Open plan designs include cubicles and open spaces for professional, clerical and administrative offices. Closed plan designs, which provide for maximum confidential privacy, include management offices, human resources office, legal offices, conference rooms, doctor's offices and medical treatment rooms.

To achieve total acoustic performance, the ideal combination of sound blocking and sound absorption, an acoustical ceiling product should perform at a high level of both CAC and NRC. Ceiling panels with high CAC and NRC ratings help block and absorb unwanted sound in open office spaces, and even more importantly in closed offices where privacy is key.

More recent architectural design trends lead away from traditional design, and we consider the open office as being comprised of both focus areas and collaboration areas instead. In this new design approach we consider function to drive form, and we'll discuss three specific work areas: focus areas, collaboration areas and privacy areas.

Total Acoustic Quality in a Healthcare Environment

Privacy, measured by the Privacy Index, is important in a healthcare setting. When information of a sensitive nature is verbalized, a patient within a closed room should feel certain that the information will not transmit beyond that space. New federal rules give guidelines on how to create speech privacy to ensure that patient's health privacy is preserved.

HIPAA is the Health Insurance Portability and Accountability Act of 1996, which protects the privacy of individually identifiable health information. The point is that each person is entitled to the privacy of his or her medical history, and this law is enforced by the Office for Civil Rights, within the U.S. Dept. of Health and Human Services.

According to the National Institutes of Health⁴, department managers can use cost-effective and simple strategies to comply with HIPAA oral privacy requirements:

► Consider using cubicles or screens to block sound.

► Install masking sound systems, sound-absorbent curtains.

► Install ceiling tile with high noise-reduction rating (NRC).

The addition of a ceiling with high sound blocking performance (CAC) will further assist in keeping patient information confidential.

Building design and specification both have significant impacts on speech privacy and construction costs, and the project architect can impact the methods and materials.

Besides offices and healthcare environments, there is a third category of interior spaces that needs special acoustic consideration: classrooms. That will be our next area of exploration.

Total Acoustic Quality for Classrooms

Teachers and students do their best in an environment that is conducive to learning. A poor acoustical environment will often increase stress and decrease concentration, especially in these cases:

► Students with hearing impairments or learning disorders.

► Very young children—These students require good acoustic conditions because much of the material and vocabulary is new to them. Because these students have limited vocabularies, they are less able to fill in missing words and phrases not heard clearly.

► English as a Second Language Students —The number of non-English-speaking students is growing in the American school system. These students are at more of a risk than native speakers in a noisy classroom because they are often learning the language as well as the curriculum.

► Students with Temporary Hearing Impairment—Illness often causes hearing loss in children. Research shows that middle-ear infection is the most frequently occurring medical condition in young children, with incidences as high as 25 percent among kindergarten and first grade students.

► Teachers at Risk of Burnout—When teachers must constantly raise their voices to overcome noise, vocal chords become fatigued. Teachers become stressed and frustrated trying to talk “over” the noise.

These are sources of unwanted noise in the classrooms:

Reflected Sound—Reflected sound takes longer to reach the listener than direct sound because its path to the listener is longer. Reflected sound can be good or bad depending on the time delay and the surface from which it is reflected.

Reverberation— Short reverberation times are good for speech intelligibility.

Background Noise—This may include interior noise sources such as HVAC system and corridor noise plus environmental noise generated outside the building, such as playground activity, traffic and planes.

ANSI Standard S12.60

ANSI Standard S12.60 for classroom acoustics addresses the issues of both reverberation time and background noise and their effect on speech intelligibility by placing maximum permissible levels on each.

The reverberation times (RTs) required ensures that the speech will be clear, and the maximum decibels (dBA) of background noise ensures that the signal-to-noise ratio will be adequate for the speaker to be heard above the noise. Under this new standard, the maximum reverberation time in an unoccupied, furnished classroom with a volume less than 10,000 cubic feet is 0.6 seconds, and 0.7 seconds for a classroom between 10,000 and 20,000 cubic feet. The maximum level of background noise allowed in the same classroom is 35 dBA.

The standard's acoustical performance criteria and design requirements apply during the design and construction of all new classrooms or learning spaces of small-to-moderate size, and, as far as is practical, to the design and reconstruction of renovated spaces.

Note that the new ANSI standard is voluntary unless referenced by a code, ordinance or regulation. However, school systems may require compliance with the standard as part of their construction documents for new schools. Additionally, many states mandate that new schools meet LEED ratings along with ANSI requirements.

One solution to comply with the ANSI standard is to reduce reflected sound. The level of reflected sound and the reverberation time can both be reduced by adding sound absorbing material to a room. The placement of those materials depends on the situation.

For classrooms in lower grades, or where ceiling heights are less than 10 feet, the best option is to place most, if not all, the sound-absorbing material in the ceiling. To reduce reverberation, specify a ceiling panel with an NRC of at least 0.70.

Wall treatments and furnishings can help. Plus, carpeting can help reduce reflected sound, but most carpeting materials used in schools have an NRC lower than 0.25 and most of it is covered with tables and chairs. Still, it can reduce noise from chair and foot impacts, both in the room of origin and the room below.

Reducing noise traveling through the plenum from adjacent spaces is important to consider. Walls do not always extend all the way up to the finished deck of the floor above. Instead they often stop at the suspended ceiling line. As a result, noise in an adjacent space can reflect off the deck and bounce back down through the ceiling into an adjoining classroom. To help reduce this type of noise intrusion, choose an acoustical ceiling panel that has a high CAC value, which will help block the sound between two rooms that share a common plenum. The suspended ceiling can also be back loaded with fiberglass insulation batts. Another solution is to install a gypsum board plenum barrier between the adjacent rooms and sealing all penetrations.

Classroom Study Project

A classroom case study was conducted by architect Micaelina Campos that illustrates the effect of acoustical treatment in an existing classroom.⁵ The test was in response to teachers in a local school who were complaining about the vocal effort required to teach. The problem was a very high reverberation time and a high level of background noise from the street. Campos offered to conduct a test to see if the proposed solution would work. She selected four essentially identical classrooms. The design of the rooms was typical for the area, namely, hardwood floors, masonry walls, high masonry ceilings and tall windows.

Campos treated two rooms acoustically, and left the other two untreated to function as “control” rooms. To improve the acoustical environment in the treated rooms, Campos employed a three-step solution:

1. Installation of a suspended ceiling with an NRC of 0.70 and CAC of 35.

2. Application of a wall treatment across the top portion of the back wall.

3. A reduction in the size of the windows followed by the installation of a second pane of glazing.

The acoustical results of the treatment were dramatic. Reverberation time went from 2.6 seconds to 0.6 seconds. And the level of background noise went from 66 dBA during peak street noise hours to a low of 38 dBA.

However, acoustical results were not the only measures of success. A number of subjective factors were also investigated. For example, teachers were asked how they felt after teaching in the treated classrooms.

► There was an 80% increase in the level of satisfaction.

► Fewer voice problems was one of the most common reasons given.

► Before acoustical treatment, 57.5% of total teacher absences were due to voice/throat problems.

► After treatment, only 34.7% were due to the same problem.

The most telling measure of success came from parents, who, after moving their weekly association meetings from one of the non-treated classrooms to a treated one, decided to conduct all their subsequent meetings in the treated classroom, and to install acoustical treatments in the remainder of classrooms.

While there is an obvious need for high NRC and CAC ceilings in many projects, specifying the best material can be complicated. The next section will focus on that.

Material Options for High-Performing Ceilings

How do you specify properly to achieve desired ratings? Let's view four types of ceiling materials: Mineral fiber, fiberglass, wood and metal.

Mineral Fiber Ceilings

Mineral fiber ceilings provide the best combination of sound absorption and sound blocking to optimize acoustics in every space, price, and performance range. High-performing mineral fiber ceilings are good choices where noise from occupants is likely to reach high decibel levels. Use high-performing mineral fiber to control reverberation time. They are recyclable at the end of their useful life and many are certified as USDA BioPreferred products.

Fiberglass Ceilings

Fiberglass ceilings provide high sound absorption and are available in standard and high AC configurations. These are a good choice for open plan spaces, but for spaces where many types of work is done an ideal combination of NRC and CAC will assure quality acoustical performance for the building occupants.

The panels come in a large number of standard sizes to mix and match in a variety of layouts for more contemporary designs than traditional ceiling installations.

In addition to the acoustical properties, both mineral fiber and fiberglass ceilings are Class A fire rated, high light reflective, resist mold, mildew, and sag.

Metal Ceilings

Metal ceilings continue to increase in popularity because of their durability and sleek, contemporary aesthetics. They are offered in a variety of finishes that can impart a very high tech or sophisticated look to a space. These ceiling panels with acoustical fleece backing have an NRC rating of 0.75 and with an added acoustic infill panel, laid behind the ceiling panel, have an NRC rating of 0.90.

Even though it is metal, this type of ceiling can provide both sound absorption and sound blocking. To achieve the acoustic benefits, the panels must be perforated and backed with an acoustic fleece. Perforations vary in size depending on aesthetic appeal, although it is possible today to have extra microperforated panels in which the holes are so small, they are virtually invisible.

Wood Ceilings

Wood ceilings are available in a wide variety of rich, natural finishes and also provide access to the plenum. As with metal, perforated wood panels provide better acoustic performance than non-perforated panels.

Wood ceiling panels can have an NRC up to 0.80 with an infill panel, and wood planks with similar acoustical treatment can have an NRC of 0.95. In addition to their application in continuous ceilings, both metal and wood panels can also be used in acoustical ceiling clouds, canopies, baffles, and blades.

Linear visuals in wood provide many options that include traditional planks, tapered planks, or easy to install grille with dowel or backer, solid wood or veneers and a variety of plank widths. Traditional planks and grille can be installed in the ceiling, on the wall, or used to create 90-degree angled or curved ceiling-to-wall transitions. Linear wood with acoustical infill can achieve an NRC of up to 0.60, while wood grille can see an NRC of up to 0.85.

Conclusion

The problem of noise pollution inside offices, healthcare settings, and classrooms is pervasive and destructive to productivity, privacy, and learning.

Specifying high-performing acoustical ceiling products with the ideal combination of NRC and CAC is often the best solution an architect can use to address the problem, but one can't just go by those numbers individually; it's the combination of both the NRC and CAC that provide ideal acoustic performance.

Manufacturer's data sheets reveal both the ceiling panel's sound absorbing and sound blocking capacities. Some even provide new classifications, making it easier to assess the combined acoustical performance of a ceiling.

As the studies cited here indicate, poor indoor environmental quality is often caused by the lack of attention to acoustical quality. Getting the acoustics right goes a long way in making the built environment healthy for the occupant, and allow for maximum productivity, privacy and learning.

Endnotes

1. http://www.gensler.com/design-thinking/research/the-2013-us-workplace-survey-1
2. http://escholarship.org/uc/item/0zm2z3jg#page-3
3. http://www.cbe.berkeley.edu/research/acoustic_poe.htm
4. http://www.ncbi.nlm.nih.gov/pubmed/12733219
5. http://www.armstrong.com/common/c2002/content/files/4250.pdf

Armstrong is the global leader in acoustical ceilings with the broadest portfolio of standard & custom options available, including ceiling and wall systems, plus clouds, canopies, baffles, and all the proven installation systems you need. www.armstrong.com/commceilingsna