Architects, engineers and researchers are learning more about how sound waves influence the learning environment and the design of schools for 21st century children and adults. This article will review some of the principles behind the acoustic properties necessary for great learning environments. The professional will review new high-performance acoustic materials, including "active acoustics" - the newest technology for the manipulation of sound in space. These new materials include lightweight gypsum wallboards dimensionally similar to a typical 5/8" drywall, but with superior acoustic absorption. In addition, this article will discuss new high-performance perforated wood veneer and metal panels that can satisfy any sustainable design checklist.
ACTIVE ACOUSTICS AND RIGHT- SIZING PERFORMANCE SPACES
"In general no one acoustic design is perfect for all performance types. Different modes of communication, whether it is speech or music, require the design of a different reverberation time. For speech intelligibility, a low reverberation time is required; for unamplified singing or instrumental music, long reverberation designs are necessary," says Roger Schwenke, Ph.D., architectural acoustics expert at Meyer Sound Laboratories, Inc. Rooms with high ceilings, large cubic volume and hard, heavy surfaces are needed for musical performances. For classrooms, where good speech intelligibility is important, rooms can be smaller and be made of lightweight absorptive surfaces. Because the physical volume and surface treatment are so different, these spaces are mutually exclusive and may require schools and colleges to invest in multiple performance spaces, as well as large classrooms, with limited usability over the school year.
One 21st century approach to acoustics is to design a flexible space that can meet the requirements of all types of performances, from classroom to concert hall. This perfect space can be constructed to optimize all of these performances through active acoustic systems, providing the listener as well as the performer with good sound quality. As schools slash budgets, new technology provides a means to reduce the building footprint in order to combine large spaces into smaller, more flexible lecture and performance spaces without losing acoustic viability.
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| BIM-driven manufacturing reduced the cost of this ceiling's visually interesting relief design. Openings for sprinklers were precision cut in the factory to simplify field installation and create a clean look. The aluminum and maple veneer system gives the dramatic look of a substantial wood ceiling, but is very lightweight and provides easy accessibility to the area above. University of Southern California School of Law Café, Los Angeles, California Architect: Gensler |
The components
To design the room with an active acoustic system, professionals should specify, as a base configuration, a room volume sized for speech intelligibility. This room should have the recommended absorptive materials for low reverberation times even for low frequencies. Active acoustic systems can add reverberation electronically, tuning the sound in the room to meet the additional requirements for hearing music or other types of performances.
They can also increase speech intelligence by providing voice lift and create an "electronic orchestra shell" for listeners as well as for musicians to hear themselves on stage. These systems can be installed to be invisible to the eye, and they can be embedded in perforated walls or ceilings.
Active acoustic systems incorporate the following components:
- Microphones in the room to pick up direct sound near a performer
- Microphones in the audience to pick up existing reverberation
- Loudspeakers that regenerate sound to tune the performance to the required acoustic signal
- Digital signal processors that contain the communications hardware
- Services by trained experts who will locate equipment into existing buildings as well as work with the architect in the early stages of design to provide the minimal room design for performances in new facilities.
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An active acoustic system added voice lift to make speech sounds intimate and intelligible during a technical seminar at the Pearson Theatre, Meyer Sound Laboratories, Inc, Berkeley, California.
Photo courtesy of Meyer Sound Laboratories, Inc.
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Is it green?
According to Roger Schwenke, who is beginning a research study on the possible environmental benefits of active acoustic systems, these systems offer a means to change the acoustics of a room electronically. They are an alternative to physically variable acoustic treatments such as retractable curtains, or doors opening to reverberant chambers. They are green because they provide the alternative to building multiple performance spaces in schools, from K-12 to a university setting. By using active acoustic systems, the cubic volume in a room can be smaller, and therefore the amount of materials needed to construct the building, the energy used in the HVAC and lighting systems are reduced. A lower volume of construction means fewer materials in construction and to transport. Potentially, there is the added benefit of more open space on the site of a shrunken building envelope. Active acoustics can change the sound quality of a room by pushing a button, rather than constructing more square footage.
| Zellerbach Hall Acoustic Retrofit |
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An analysis of this auditorium determined the placement of the components of an effective active acoustic system at Zellerbach Hall, University of California Berkeley.
Image courtesy of Meyer Sound Laboratories, Inc.
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| The 2,014 seat Zellerbach Hall was designed in 1968 as the permanent home and largest indoor venue of Cal Performances, UC Berkeley's premiere music, dance and drama events space. This building won an AIA award for design excellence and it has been the site for numerous performing arts programs including the home of the Berkeley Symphony Orchestra. It was designed for exceptionally diverse programming in the 1960s when architects Vernon DeMars and Donald Harrison had few options for dealing with the diverse acoustic demands of these performance types. Variable acoustics methods involving physical or mechanical means were expensive and electronic enhancement was in its infancy. The architects opted for the only reliable solution available at the time: a "happy medium" wherein the acoustics were acceptable for most of the hall's programs, if optimum for only some. The resulting mid-band reverberation time ended up being 1.45 seconds. This was an ideal length for chamber music, opera and recitals, but at the high end of acceptability for dramatic and spoken-word performances. Music benefiting from a longer and more complex reverberation characteristic, such as orchestral and choral performances, and some types of ethnic and electronic music, was, of necessity, more compromised. They employed a traditional orchestra shell, to add projection and increase the ability of the musicians to properly hear one another, but it was labor- and time- consuming to construct and de-construct for each performance. "We had been grappling with this issue of maximizing the hall's sound for a number of years," says Cal Performances director Robert Cole. "We know the acoustics are quite good as they are; many wonderful artists have performed here with great success. There have been, however, some instances, such as when a period orchestra like Philharmonia Baroque Orchestra performed, when I have wished we could modify the architecture of Zellerbach to better replicate the space in which the music was originally meant to be performed." The challenge presented by Zellerbach Hall was to extend and enrich the venue's excellent physical acoustics while gaining a second acoustical environment similar to that of a classic concert hall. The auditorium also housed graduations and speakers throughout the years, in spite of the challenging acoustical environment. In 2006, the University was approaching its 100-year anniversary and for its gala celebration, they planned to include a wide array of performers from dance to opera. They met with an active acoustics engineering team and Cal Performances, setting three main acoustic goals. The first was to provide an enhanced level of natural-sounding reverberation throughout the hall when desired for selected types of performances. The second goal was to improve projection of sound into the hall, and to allow musicians onstage to clearly hear each other, when the orchestra shell is not in place - essentially by adding a "virtual orchestra shell" as an alternative to the hall's mechanical one. Lastly, the installation needed to be natural sounding as well as not visually obtrusive in this award-winning building. The installation was successful in meeting all of its goals and as Cal Performances music director, Robert Cole, said, "we planned our Centennial Gala comprised of dance, music and a large orchestra and chorus all in one evening. Installing the active acoustics retrofit was the only way we could pull it off."1 |
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A broad range of acoustical characteristics can be provided by active acoustic systems and services. This graph of reverberaton time over frequency shows the range of responses available to Zellerbach Hall, from that of the pure physical acoustics to that with the active acoustics system.
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Soundproofing Lightweight Gypsum Meets ANSI School Criteria
To point out the long history of acoustical concern by professionals, Brandon Tinianov, CTO of Serious Materials and current Chair of the Acoustical Society of America's Technical Committee on Architectural Acoustics, quotes Vitruvius: "Sound moves in an endless number of circular rounds, like the innumerably increasing circular waves which appear when a stone is thrown into smooth water." Long after this first- century explanation for sound, professionals continue to examine the complex interactions between architecture and sound waves.
When analyzing the sound transmission of wall components in schools, acoustic experts focus on three main characteristics of sound: level (or sound pressure level), frequency and reverberation. Sound pressure level measures the loudness of a sound, which can be affected by the numerous and complex interactions of sound waves with materials and background noises. The intensity of a sound is measured by the decibel level (dB) and in learning environments, the signal-to-noise ratio of the teacher to background noise is critical. Background noise can be transmitted through the walls from classroom to classroom and from hallways to classrooms. The frequency of sound refers to the pitch or vibration of a sound wave. Reverberation, as defined later in this article, can degrade comprehension of sounds, not just when one or more people are speaking, but also when competing mechanical noises or highway noises disrupt the listener.
Sound pressure level, frequency and reverberation can hurt or benefit speech intelligibility and affect learning. That is why the American National Standard Institute (ANSI) Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools (ANSI S12.60-2002) set maximum standards for reverberation time for different room sizes as well as for Sound Transmission Classifications (STC) and decibel levels for classrooms. ANSI also recommends minimum STC ratings for single or composite wall, floor-ceiling, and roof-ceiling assemblies that separate an enclosed core learning space from an adjacent space. (See ANSI standards in online version of this course.)
Traditionally, professionals specify multiple layers of sheetrock or drywall, or mass to adjoining walls with masonry or staggered studs. All of these solutions add weight, labor and materials to the project. A recent development in lightweight gypsum meets or exceeds the recommended noise attenuation levels for walls while reducing the materials required to achievehigh acoustic performance goals. When compared to other assemblies, soundproofing gypsum drywall provides higher STC values/labor and materials as seen in this 2009 chart using RS Means Building and Construction Cost Data. (See table at end of article.)
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Acoustic energy comes in contact with the wall. Constrained layer, damped panel converts acoustic energy to heat energy (in tiny amounts) which is absorbed.
Graphic courtesy of Serious Materials
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Soundproofing gypsum drywall allows the designer to provide the auditory learning environment as recommended in ANSI/ASA S12.60-2002, as well as meet sustainability design goals. Depending on the wall assembly, and design application, the designer can choose between several types of soundproofing and moisture resistant materials. Although similar to sheetrock, these 5/8 inch drywall panels have a thin innerlayer that adds soundproofing to the wall system without adding the weight of additional layers of wallboard panels. This soundproofing drywall is screwed in place and does not need to have a resilient channel. Gypsum drywall can be perforated by screws without any loss to its soundproofing capacity. This drywall can be specified to be load bearing, or Type X, have a one hour fire-rating, can be specified as abuse-resistant, and can provide an STC 55 rating on single steel stud construction. The materials are as follows:
- For wood construction: a laminated or damped drywall designed for school applications that have a calcium silicate back face.
- For masonry construction: the same drywall as above but placed on one-inch wood furring strips. This application can be used for both interior and exterior walls.
- For metal studs: a gypsum face drywall with magnesium back.
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Installation of soundproofing lightweight gypsum used to absorb sound transmission
Graphic courtesy of Serious Materials
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Sustainability - more acoustic performance with less material
The soundproofing material inside of a 5/8-inch gypsum wallboard is less than one-thirtieth of an inch thick. Lightweight and soundproof, gypsum wallboards deliver soundproofing with many fewer layers of drywall - often less than half of the materials typically used in wall construction - while achieving the same acoustical performance values. Typical soundproofing wall construction used in school projects can use as much as four to six layers of traditional drywall. Other options include the design of walls with double studs to achieve higher performance values. Professionals specifying this product will use less material, less labor and will have less waste on the construction site, as well as gaining additional square footage. With this improved soundproofing technology, professionals can reduce drywall material useage in these situations or applications by up to 75 percent. Moreover, the primary and most sustainable reason to use soundproofing drywall is to enhance human performance and create a "high performance acoustic learning classroom." Soundproofing lightweight gypsum wall boards reduce noise from 70 to 97 percent and can result in STC ratings from 46 to 80 for walls - depending upon the wall assembly
What's next?
According to Brandon Tinianov, CTO of Serious Materials, "One important and overlooked category of acoustical materials is high-performance windows for classroom acoustics." New acoustical windows may be able to achieve sound transmission levels from 35 to 40 STC, STC ratings that are growing closer to wall acoustical performances. These windows will not look any different to the viewer, they will have the same visible transmission values, but they will be heavier and potentially have a thicker profile. Engineers will manipulate the air space in windows to achieve these greater performance levels.
PERFORATED WOOD VENEER AND METAL PANELS
| BIM-driven Manufacturing - Making Custom Designs Affordable |
| BIM-driven manufacturing now allows competitively priced, mass customization of ceilings and interior walls panels. One progressive manufacturer, for example, creates three dimensional building information models (BIM) of ceiling or wall designs, then transfers the geometric data into automated punching machines that trim aluminum or wood-veneered sheets into any size and shape, with tolerances as close as 0.005-inch. After punching, panels are fed through automated machinery that curve panels and form the bends at panel edges. The newest generation of this computer aided manufacturing process allows designers to use curved surfaces, tessellated geometries, and other complex designs without paying the premium prices formerly associated with custom ceilings or walls. The same machines can make as many as 7,000 unique perforations per minute to give panels the desired appearance and acoustical properties. Designers can select the size, shape, and spacing of the perforations, and can even use the perforations like pixels to create patterns, logos, wayfinding cues, and other graphic images. Recent process improvements have made it possible to specify micro-perforations that are almost invisible when viewed at standard ceiling heights yet still afford high noise reduction properties. Larger perforations can be illuminated from above to create luminous ceilings. Ceilings increasingly require careful integration with light fixtures, fire sprinklers, HVAC louvers and grilles, and other building services. Required penetrations for these services are located in the BIM and then formed in the factory to simplify field installation, reduce job site waste, and assure that services are optimally located to maintain the overall good looks of the ceiling. |
New types of metal and wood ceiling and interior wall panel systems offer cost-effective alternatives with fresh aesthetic options, outstanding acoustical control, and impressive environmental benefits. Nancy Mercolino, President of Ceilings Plus, a ceiling producer, comments that "the 24 x 48-inch ceiling grid is no longer a given in contemporary architecture. Metal and wood panels now allow designers the freedom to use almost any panel size and shape, plus an increased range of finishes and acoustical options, without breaking the budget."
She explains that perforated metal has been used acoustically for about a hundred years. Yet the appearance and functionality of the products have changed dramatically in the past few years in response to evolving architectural needs and new fabricating technologies. For example, she points out, perforated panels can now be made with recycled aluminum sheets that weighs less than most other ceiling materials yet eliminates most of the oil-canning and visual distortions that used to limit the size of metal panels.
Another breakthrough has been the recent development of ways to laminate wood veneers to aluminum. In the past, Mercolino says, "wood panels were heavy, expensive, combustible, prone to warp with changes in humidity, and offered limited acoustical control. The new laminated products avoid all these problems, making wood ceilings and walls attractive from both the economic and aesthetic vantage." Wood, she suggests, adds a visual warmth and excitement that can soften the institutional feel of a school.
Perforated metal and wood panel systems can also contribute to the sustainability goals espoused by schools. In addition to controlling noise to create better learning environments, the panels have zero-VOC finishes and no added urea-formaldehyde, are durable, contain high recycled material content, do not support mold or mildew, have Class 1 surface burning characteristics, and provide outstanding life cycle value. They are available with finishes that have high light reflectance values to reduce energy consumption and optimize daylighting. And the panels are easily removable for access above a ceiling or inside a wall to commission and maintain HVAC, power and communication cables, and other building systems.
| Los Angeles Harbor College - Technology Instruction and Classroom Building |
| This "smart classroom" is a high-end conference space/auditorium that supports the college TV studio. The room is used for lectures and presentations, as well as for sending and receiving classroom content and live television broadcasts to and from remote locations. Mark McVey, LEED AP, Design Principal at SmithGroup, explains that the acoustic considerations in this room were unique because the space is used for different purposes. "As a TV studio, the room should be dead, without any echo," he says. "But as a lecture space, it should be live enough to bounce the speaker's voice off the surfaces without too much amplification." The designers were able to achieve satisfactory results for both uses by installing perforated acoustic panels with fiberglass backing yielding an NRC (noise reduction coefficient) of 0.85. Because of the need for the raised projectors and projection screen, there is a one-story portion and a two-story portion of the room. Since the designer knew there would be some echoing or problematic acoustics up in the higher portion, he decided to use acoustic ceiling panels. Then, when he discovered that metal panels could be made with a radius, McVey and his team decided to continue the rounded shape down throughout the lower area as well. "It was a design opportunity that came out of the properties of the material," he says. The panel perforations are oblong. This was chosen for both acoustic and aesthetic reasons. "We needed a lot of porosity in the panel to get the acoustic benefits that were required," says McVey, "We thought that using standard circular perforation patterns would result in so many holes, and we wanted to be able to see as much of the material as possible." The aluminum was pre-finished before fabrication with a copper-toned paint that was chosen to give a warm look. Another ceiling achievement in this project was the designers' ability to incorporate a series of components in the room as flush elements, including mechanical registers, speakers, sprinklers, lighting, and projectors concealed behind perforated surfaces or in slots within the ceiling system. |
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This smart classroom in the new Technology Instruction and Classroom Building achieves both acoustic control and dramatic visual impact with the help of custom curved, perforated aluminum ceiling and wall panels that yield an NRC of .85.
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Perforated panels and acoustical performance
One of the leaders in setting performance values for school construction is the Collaborative for High Performance Schools (CHPS).2 This organization has developed a report card that parents and professionals can use to rate their schools. How satisfied are parents with the acoustics in their child's classroom? How disruptive are the potential noise sources in the room? Is the mechanical equipment too loud? Can you hear sounds from neighboring classrooms? Does noise penetrate from the outdoors? CHPS sets minimum performance values for good classroom acoustics so teachers can speak without straining their voices and students can hear and effectively communicate to enhance their learning experience.The CHPS Report Card provides a table of acoustical standards that includes capping ambient noise levels at 45 dBA and limiting the maximum unoccupied Reverberation Time to 0.6 seconds.3 The USGBC LEED® for Schools, Environmental Quality Prerequisite 3: Minimum Acoustical Performance requires that the professional design classrooms meet the reverberation time requirements of ANSI S12.60-2002. According to the American National Standard Institute (ANSI) Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools (ANSI S12.60-2002) a background level less than 35 dBA is preferred for superior acoustics, particularly for young children and those with hearing impairments.
Long reverberation times reduce speech intelligibility in a classroom and it is here that perforated panels are most useful to the designer. Reverberation Time (RT60) is a measure of how quickly, in seconds, sound reflections in a room decay 60 dB or become inaudible. Rooms designed for good speech intelligibility should generally have shorter reverberation times. Reverberation time is typically controlled by the judicial application of ceiling and wall finishes that have higher noise reduction coefficients (NRC).
Noise reduction coefficient (NRC) is a measure of how well a product absorbs sound. Simply put, higher NRC values mean better sound absorption. By selecting ceiling and wall finishes with higher NRC values, the architect and acoustical consultant can control the reverberation time in spaces that require good speech intelligibility. Even without acoustic absorptive materials added, wood and metal perforated panels can have an NRC of 0.40. Add a paper-thin, non-woven acoustical fabric and the NRC can reach as high as 0.75 with as little as six inches of airspace above the ceiling panel. With reconstituted cotton batts that can have up to 85 percent pre-consumer recycled content, the NRC can be 0.95 - an almost perfectly absorptive material.
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The artful combination of wood and metal panels vertical and slope surfaces was used throughout the corridors and public areas of this athletic facility to visually unify the building. The warmth of the wood softens the effect of the hard concrete masonry walls. Where required, panels were perforated to yield a high acoustical value of NRC=0.90.
Photo courtesy of Ceilings Plus
Tompkins Cortland Community College, Dryden, New York Architect: JMZ Architects and Planners, P.C. |
In school auditoriums and theaters, metal and wood ceilings can be shaped to create good sound diffusion with curved and angled panels. Some panels can be perforated to absorb sound and others can be non-perforated to reflect sound. Perforated wall and ceiling panels can be specified to "tune" the acoustics in a room. By adjusting the hole size, hole spacing, and cavity depth, panels can be designed to absorb more sound at a particular group of frequencies, much like adjusting the bass, mid, and treble controls on your home stereo.
The artful combination of wood and metal panels on vertical and sloped surfaces, was used throughout the corridors and public areas of this athletic facility to visually unify the building. The warmth of the wood softens the effect of the hard concrete masonry walls. Where required, panels were perforated to yield a high acoustical value of NRC=0.90.
Perforated panels can also be used to create acoustically transparent surfaces that allow speakers and electro-acoustic systems to be installed above the ceiling or behind wall panels, reducing visual clutter. In many instances there are already noise-reducing materials above the ceiling in the fireproofing, thermal insulation, or even the air space that will allow noise to be dissipated above the ceiling. More, acoustically transparent surfaces can be used to create longer reverberation time, a requirement in auditoria designed for symphonic music, by adding the space above a ceiling to the acoustical volume of a room.
Materials matter - recycling and FSC-certified wood
Aluminum panels can be specified to contain up to 85 percent recycled aluminum, including as much as 75 percent post-consumer recycled content - usually from beverage cans. Aluminum is one of the most readily recyclable materials and can be recycled repeatedly without loss of strength or metallurgic value. In addition, the steel suspension systems used to support panels can have between 25 percent and 30 percent recycled material content. Professionals can also specify acoustical insulation that is made from recycled cotton; the batts are factory-installed to reduce time and labor costs on the job site.These panels are light weight systems, are easy to handle, and can reduce a building's deadload. Lighter panels also reduce the shipping impact on a construction budget. For large projects, panel manufacturing can be set up near the project site to increase the regional material content and further reduce the environmental impact of shipping.
Wood veneers that are certified by the Forest Stewardship can be laminated to aluminum cores to create a more sustainable panel configuration. FSC certifies that products do not come from illegal logging and are produced by companies that meet strict environmental and social welfare guidelines.4The USGBC LEED® for Schools, Materials and Resources Credit: 7 Certified Wood (FSC) can be applied to only wood certified by FSC, giving this ceiling choice an added advantage for designers. Wood and metal perforated panels can contribute to many LEED® credits - commissioning, local and regional materials, and recycled content.5
Additional environmental benefits include the durability of these products; unlike mineral fiber acoustical panels, metal and wood perforated panels are easy to clean, resist damage, and can even be repainted during remodeling without loss of noise reduction value. Factory applied paint finishes release zero VOCs and provide color consistency throughout the entire project. Manufacturers use pre-painted coil before fabricating that gives greater color consistency and a tough more durable finish. Since aluminum is corrosion and humidity resistant, panels can be used above swimming pools, in laboratories and outdoors.
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| The ceilings and soffits in the Kelley Engineering Center were designed for optimal acoustic performance, and used FSC-certified wood veneers to add natural beauty to the space. This building received a LEED Gold rating.
Photo courtesy of Ceilings Plus
Oregon State University, Corvallis, Oregon Architect: Yost Grube Hall Architecture |
Common sense panel mechanisms and designs
Poor ceiling configurations, tight ceiling cavities, the location of lighting and HVAC ductwork - all of these make the renovation or maintenance of existing buildings difficult. New ceiling panels are designed to swing down from the ceiling plane to expose the systems above for mechanical repairs or replacements. The ceiling panels have torsion springs that hold the panels tightly in place yet allow easy removal for access anywhere above the ceiling.Alternatively, new panel systems allow metal and wood panels to be installed in standard ceiling grids, an option that is especially suitable for budget conscious projects or when remodeling a space with an existing ceiling grid. Panels can be installed with an exposed tee, a tegular reveal, or a narrow reveal for a concealed tee appearance.
Either way, ventilation louvers, lighting fixtures, sprinkler heads, speakers, and other building services should be integrated into the design of the ceiling system to eliminate clutter.
Designing outside of the box - new design vocabularies
The ceiling plane is typically the most visible surface area in a school room, providing a clean slate where designers can make a statement. While Cartesian grids of square and rectangular ceiling panels may have sufficed in another age, they are no longer emblematic of today's more nuanced pedagogical thinking. Instead, BIM-driven fabrication allows each panel to be unique and for designers to create installations with multiple layers of pattern. For example, triangular, rhombic, or other polygonal panels can create a basic module. Then, by varying joint spacing, individual panels can be clustered into segments that read at a larger scale. Perforation patterns can be varied to define areas within a space, or used as graphics that can extend across the boundary of individual panels to add additional visual texture. Finally, designs can also incorporate multiple panel colors or finishes, and create visual rhythm by the way lights and other fixtures are interspersed throughout a ceiling.In schools, educators are challenged to expand the minds of their students, to expose them to new ways of thinking. The student is asked to explore new ideas and integrate information toward new actions. In this context, new materials provide an opportunity for learning. Mass-customizable wood veneer and aluminum ceiling and wall panels pose an opportunity for architects who can choose to inspire students and teachers by exploring and integrating this new acoustical design vocabulary on the ceilings and walls of their school buildings.
In response to ADA lawsuits that identified acoustics as a restriction for learning and driven by research that defined the learning thresholds, particularly for children as well as those with hearing disabilities, the Acoustical Society of America (ASA) convened a working group to create acoustic design standards for optimal learning environments. This collaborative effort resulted in the 2002 "American National Standard Institute (ANSI) Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools - ANSI S12.60-2002." This voluntary standard was re-affirmed in May of 2009 and documents stringent standards that will ensure the best auditory enviroment, particularly for children.
The committee included members from specialties in engineering, architecture, bio-acoustics, noise, signal processing and speech communication to name just a few of the specialities represented in this broad consensus effort. The result was an affirmation that "good acoustical qualities are essential in classrooms and other learning spaces in which speech communication is an important part of the learning process. Excessive background noise or reverberation in such spaces interferes with speech communication and thus presents an acoustical barrier to learning. With good classroom acoustics, learning is easier, deeper, more sustained and less fatiguing."6
Up to 60 percent of all teaching occurs through communication through spoken language and learning depends on speech perception. Up to 15 percent of all children are estimated to have a slight hearing loss.7 The standard focuses on criteria for speech intelligibility in background noise and in reverberant environments in classroom studies. Research cited by this committee included studies in classrooms that linked scholastic achievement including test scores with the auditory learning environment.8
The committee recommended a 35 dBA acoustical performance criteria for steady classroom background noise levels assuming that the signal-to-noise ratio of at least +15 dB. In this instance, the signal to noise ratio (SNR) compares the level of intelligigible speech to the level of background noise and that can include everything in a classroom from sound traveling across partitions, to the hum of mechanical equipment, and to the sound of a classroom projector. The higher the SNR ratio the easier it is to hear and to understand the instructor.
When the standard was released in 2002, many professionals found that they were hard to accomplish in a typical classroom with mechanical systems and equipment designed to older acoustic standards. 35 dBA is quiet, so quiet that many schools were not designed to meet this standard.
CHPS, LEED® AND THE FUTURE
The goal of the Collaborative High Performance (CHPS) program a leader in setting school performance criteria is "to improve student performance and educational experience by building the best schools." In the latest CHPS Operations Report Card draft public review materials, they set the criteria for acceptable acoustical background noise at less than or equal to 35 dBA.9 However, higher values are listed as acceptable for sound insulation classroom to classrom and classroom to hallway.Recommended reverberation times range from less than or equal to 0.6 sec in classrooms smaller than 10,000 cu.ft. to 0.7 sec in larger rooms. These recommendations are similar to the acoustic standards recommended by ANSI, which is beginning to be a mandated code in some states.
Manufacturers are continuing to develop new sound attenuating materials for the classroom to assure the best learning environments as documented by the ANSI S12.60-2002 standards. New materials and new technologies will allow designers to take command of customizing the design process, while engineering better environments for speech intelligibility. They will design places for expanded listening and learning.
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| Advantages of sound damping drywall: Lower cost, additional sellable floor space, improved performance and field reliability over traditional methods
Source: RSMeans Building Construction Cost Data, 66th Annual Edition 2008, for volume purchases
1 STC values provided are based on testing according to the ASTM standard E-90 at accredited laboratories * Using a materials factor of 112 (112% of national average) and a labor factor of 138
Chart courtesy of Serious Materials.
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ENDNOTES
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| 1 http://www.meyersound.com/pdf/brochures/cs_zellerbach_b.pdf 2 http://www.chps.net/dev/Drupal/node 3 http://www.chps.net/content/044/CHPS_ORC_Public_Review_1_Materials.pdf 4 http://www.fsc.org/399.html 5 http://continuingeducation.construction.com/article.php?L=61&C=322&P=14 6 American National Standard (ANSI) Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools ANSI S12.60-2002. 7 http://www.chps.net/dev/Drupal/node/120 8 A. L. Bronzaft, ‘‘The effect of a noise abatement program on reading ability'', J. Environmental Psychology, 1, 215-222 (1982). J.S. Lukas, ‘‘Noise, classroom behavior and third and sixth grade reading achievement'', Proceedings, 17th International Congress of Acoustics, Rome, Italy, (Sept. 2-7 2001). D.J. and MacKenzie, D.J and S. Airey, ‘‘Classroom acoustics, a research project'', Heroit-Watt Univ., Edinburgh, U.K. (1999). 9 http://www.chps.net/content/044/CHPS_ORC_Public_Review_1_Materials.pdf |
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