Poor classroom acoustics have a negative impact on student comprehension, engagement, and learning.
By Kenneth W. Betz, Senior Editor
Hearing difficulties are most often associated with persons of advanced age, so it may come as a surprise that many schoolchildren face serious hearing challenges. Classrooms in the United States typically have speech intelligibility ratings of 75% or less, meaning every fourth spoken word is not understood, according to an often-quoted study.
“The problem is that classrooms are designed, built, and financed by normal-hearing, native-speaking adults but are occupied and used mostly by children. For adults, a speech intelligibility rating of 75% is not that bad. However, children do not have the hearing or comprehension maturity of adults. In classrooms you have to consider the population that are not native language speakers and that as much as 25% of the students have ear infections. This can result in decreased levels of concentration, comprehension, and stress,” said Sean Browne, principal scientist, Global Acoustics, Armstrong Commercial Ceiling Systems, Lancaster, PA.
“We know that children under the age of 15 years require more favorable acoustic environments than older children to achieve similar levels of speech recognition,” said Samantha Gustafson, AuD, CCC-A, FAAA, project coordinator, Listening & Learning Lab, Vanderbilt Univ., Nashville, TN.
“Therefore, the speech intelligibility rating of a classroom will be highly influenced by the age of its occupants. Because buildings are not often constructed keeping in mind the age of occupants in each room, we are missing the mark on providing learning environments that offer optimal opportunity for speech perception to the majority of students,” she said.
“Classroom acoustics are also important for teachers, who might be at increased risk for voice problems due to high levels of noise. It is well understood that a speaker naturally increases the level of their voice in the presence of increased ambient noise levels; this is called the Lombard Effect. Recently, it has been reported that teachers in highly reverberant environments report lower job satisfaction, reduced energy, and increased interest in leaving their job,” Gustafson said.
Lack of Awareness?
Industry insiders are divided about why so many classrooms have poor acoustics. Were designers simply not aware of acoustical issues or was it a lack of funds that resulted in classrooms that limited the learning capacity of students simply because of poor acoustics?
Browne doesn’t think it’s a lack of awareness. “Acoustics in the classroom are pushed heavily in the industry. All of the material manufacturers push this message as does the Acoustical Society of America, American Speech-Language-Hearing Association, and the U.S. Access Board. There is an ANSI standard that focuses on classroom acoustics, and there are LEED points available for acoustics in classrooms. There are many older buildings that were constructed when different standards were in place. As they outlive their utility and new modern buildings go up in their place, I believe current classroom acoustics standards will be utilized,” he said.
Scott Riedel, president, Scott R. Riedel & Associates Ltd., an acoustics consultant based in Milwaukee, disagrees: “Most often it seems that a poor acoustic learning environment is caused by a lack of awareness. Acoustic factors are difficult to remember or imagine in a design planning stage; such factors are not always visibly apparent at the drafting board or screen. An out-of-sight-out-of-mind approach often is the reality during design.”
As far as cost is concerned, “while acoustic design service may have a cost, acoustic design implementation can be quite inexpensive,” Riedel said. “For example, a classroom must have a ceiling. Whether that ceiling is made of sound reflective, sound absorbing, or sound diffusing materials, the cost difference might be modest, but the difference in acoustic results can be vast. The cost, measured in poor educational results, from a poorly designed educational space, can be far greater than the cost, measured in dollars, for either a design service or materials selection.”
The age of school buildings and, consequently, the prevailing standards when they were built, is another explanation for the poor acoustical performance of some classrooms. “The average age of school buildings in the U.S. is 42 years. Almost half of our existing school buildings were built hurriedly between 1950 and 1969, when the Baby Boomer population surge hit our nation’s education system,” said Gary Madaras, Ph.D., Assoc. AIA, an acoustics specialist with Rockfon, Chicago.
“Since then, there have also been a couple of bad building phases where people thought open plan schools were a good idea. So, the problem is that too many bad sounding schools, built before the current awareness of the importance of classroom acoustics, are still being used,” he said.
“About 15 years ago, the acoustics industry got together and developed a standard: ANSI S12.60 (2002) Acoustical Performance Criteria, Design Requirements and Guidelines for Schools. That was a huge step in that it defined for educators and designers how to build classrooms with good acoustics for efficient and accurate communication. This standard is also referenced now by LEED when designing schools and CHPS (Collaborative for High Performance Schools, Sacramento, CA),” Madaras explained.
Robert Marshall, manager of marketing technical services, CertainTeed Ceilings, Valley Forge, PA, sees a similar progression in classroom acoustics and particularly credits LEED with increased attention to the acoustic performance of classrooms. The suspended ceilings that introduced acoustics into the classroom in the 1960s were arguably better than the exposed plaster that predated them, which has almost no acoustical value, but the degree of acoustic value provided by the new ceilings was not really an issue at that point, according to Marshall.
Attitudes toward acoustics changed with the introduction of the USGBC LEED point system, which recognizes and awards points for classroom acoustical design, he observed. “It wasn’t just that they [USGBC] said it was a good idea. They said you cannot get any LEED certification for schools unless you address the acoustic quality of classrooms,” he said.
“All of a sudden, school boards were asking architects if they could design their school or renovation according to the LEED protocol, and it opened the door that had been shut for many decades,” Marshall said.
Mark Kemerling, product manager, acoustical panels, USG, Chicago, commented, “It may not specifically be a lack of awareness; it is more a lack of appreciation. Most architects, designers, and school officials understand the concepts at a very high level. Most also can easily understand the remedies needed to facilitate that improvement. However, during the budgetary, design, and construction phases, the value placed on this often gets pushed aside or minimized in order to meet other drivers, such as cost.”
Poor classroom acoustics generally can be attributed to a handful of recurring and generally recognized factors. One of these is signal-to-noise ratio and the other is reverberation. Noise from outside or from mechanical systems factors into the signal-to-noise ratio.
“The signal is the teacher’s voice—the sound that is good and needs to be heard. The noise part of the ratio is anything that can interfere with the signal, and there are a lot of sounds that can do that: traffic noise or plane flyovers transmitting through the windows, heating and air conditioning equipment located inside the classrooms, and occupant noise transmitting through the door to the corridor,” explained Rokfon’s Madaras.
“One other type of noise that is often overlooked, but interferes with the teacher’s voice, is reverberation. When the teacher speaks, the first sounds that arrive at the students’ ears are very useful and important. They are the necessary signal. But, if the room has a lot of sound reflective surfaces, the teacher’s voice bounces around inside the room, interfering with the intelligibility of the subsequent words,” Madaras said.
The geometric form of the room also is a factor in classroom acoustics. “Is sound energy evenly distributed in a space, or are there ‘hot’ and ‘dead’ spots?” asked Scott Riedel. “Interior finish materials are important. The ratio of sound-reflective to sound-absorbing materials is important, as is their placement to achieve clear and even sound distribution,” he added.
“An acoustical ceiling with high NRC (noise reduction coefficient) and high CAC (ceiling attenuation class) will provide absorption to reduce the reverberation and blocking to reduce the intrusion of sound from mechanical equipment and neighboring activity. In addition, wall treatments can be used to further reduce the reverberation in the space,” offered Armstrong’s Browne.
Other things to watch out for are door and window seals, door sweeps, and penetrations in walls. “There are solutions that fit almost any construction situation and any budget. Existing facilities do present some access challenges, but there are acoustical ceilings that can fit tight to structure and there are free hanging baffles, clouds, and canopies that can be used to absorb sound. Also, HVAC contractors can tune noisy equipment or add noise suppression accessories to deal with mechanical noise at the source,” Browne added.
“Ensuring that classrooms have enough sound absorption in them so that reverberation time does not exceed 0.6 seconds (per ANSI S12.60) just involves some preliminary calculations to determine how much material is needed and then installation of lightweight materials overhead. The metric for quantifying a material’s ability to absorb noise is noise reduction coefficient (NRC). It varies between 0.0 (low sound absorption) and 1.00 (high sound absorption). If you use lower-performing materials (NRC 0.70 or lower), you have to buy and install a lot more of the material to reach the goal reverberation time of 0.6 seconds. The higher the NRC of the material, the faster you decrease reverberation,” Rockfon’s Madaras said.
He continued, “Older schools may have suspended acoustic ceiling tile, but there’s a good chance that they still don’t reach the goal reverberation time because the older ceiling tiles have very low NRC values of 0.60, 0.50 or less. It’s relatively easy to bring a classroom into compliance with the maximum reverberation time criterion in ANSI S12.60 by swapping the existing ceiling tiles with high-performing ceiling panels of NRC 0.90 or higher. The suspension grid can be reused.”
“Depending on the problem or deficiency, it is always more challenging to remedy the situation after the fact, and usually more costly,” USG’s Mark Kemerling said. “First and foremost, if a school finds itself in this situation, they should consult a professional acoustician. In a typical U.S. classroom, subtle and lower-cost solutions would include enhancing the ceiling panels by selecting products that absorb or block sound more or less than what is currently installed. Which one is used depends on the type of problem the school is experiencing. Other options would include introducing reflectors to redirect unwanted sound, or even possibly the introduction of sound-masking systems. These systems generate a white noise which, in some cases, may be what is prescribed,” he said.
While acoustic ceiling tiles solve many noise problems, other solutions may be useful as well. “For noise sources originating from inside the school building, it is generally most cost-effective to relocate the classroom to a quieter area of the building, e.g., not adjacent to high-noise areas such as a gymnasium. Developers should include one area of dead space, e.g., a storage area, between high-noise sources and classroom learning environments. If relocation is not an option, double walls on the interior and/or well-fitted and sealed doorways to hallways might be considered. Absorptive surfaces like carpeting, drapes, and acoustic ceiling tile can also be used in hallways, which can contribute significantly to the level of competing noise entering a classroom from other areas inside the school building,” Vanderbilt’s Gustafson said.
“To address the reverberation problem, absorptive surfaces like carpeting, drapes, and acoustic ceiling tile can combat reverberation in rooms with highly reflective surfaces,” Gustafson added. “Portable corkboards can also be hung on the walls and are more effective at combating reverberation if hung at an angle.”
However, the frequency of the sound to be controlled is important in the selection of sound-absorptive materials, Gustafson cautioned. “Many materials used for absorption of sound are much more efficient at absorbing high-frequency sounds, compared to low-frequency sounds. This is ironic, as low-frequency noise in the classroom has a greater effect on speech perception than high-frequency noise. Therefore, measuring the reverberation time in multiple frequency ranges may be useful when evaluating the effect of acoustic modifications in classrooms,” she said.
“Unfortunately,” Gustafson observed, “many schools seem to be moving away from absorptive materials in classrooms and toward more hard surfaces (concrete or wood floors, fully windowed walls). While this trend may be more aesthetically appealing and easier to maintain, the consequences of these reflective surfaces are often not addressed and may prove harmful to the education of students and the well-being of teachers.”
Quiet classrooms are much more necessary for students that have learning or developmental disabilities, students who have had ear buds in their ears for too long and have lost hearing that nobody should lose at that age, and students who, on any given day, may have an ear infection or a cold that limits their hearing by 20% to 25%. All of these kids are mainstreamed into a single classroom where the normal-hearing student is sometimes a minority. “The people occupying these seats are not just those students in need of a quiet classroom; they’re students with needs beyond those of a normal-hearing person,” CertainTeed’s Marshall said.
“In the end, it seems to always be about tradeoffs. In today’s environment of tight budgets and compressed design and construction schedules, the ‘acoustic lobby’ gets overshadowed by other things. Like many other important design rules, until it is in the code in a quantifiable and measurable performance metric, it will continue to get minimized. One way to guarantee better acoustics would be to build post-occupancy acoustic performance metrics. Essentially, setting minimum standards for acoustic performance based on the functionality of each space and linking this performance to the government funds would help support these schools. This would drive change,” said USG’s Mark Kemerling.
While progress has been made toward quiet classrooms where speech intelligibility levels meet the needs of all students, not just normal-hearing individuals, and where teachers do not have to raise their voices to be heard, architects, designers, and school officials need to join together to make classroom acoustics a universal priority, not an afterthought or a tradeoff.
Noise, if you haven’t heard, is a big deal these days. Not that there hasn’t always been noise. However, prior to the dawn of the Industrial Revolution, cows and horses were reasonably quiet and agreeable components of the rural lives most people lived. Save for inconsiderate roosters, chickens clucked quietly to themselves and rabbits had little to say. Power tools, lawnmowers, airplanes, and automobiles hadn’t been invented. Mechanical clanking and roaring was kept to a minimum.
The key word here is noise. Noise is a judgmental word that usually means sound we don’t want to hear, such as music favored by a generation younger than your own or unselfconscious cell-phone conversations in public. Sound itself can be useful, as when informing the neighbors their house is on fire. But allowed to run amuck, sound becomes noise.
Still, it comes as a something of a surprise that acoustics and noise are big concerns in classrooms today, even those that aren’t directly under the final approach path of an airport. I don’t remember not being able to hear the teacher when I was in school—back when there were wooden floors, high plaster ceilings, blackboards with screeching chalk, and large windows.
But kids those days didn’t have hearing deficiencies, weren’t allergic to peanuts or cats, and didn’t suffer from attention deficiency or other disorders—at least we weren’t aware of the problems. We probably didn’t even know what acoustics were. Above all, it was a time and place where all of the women were strong, all of the men were good looking, and all of the children had above-average hearing—with apologies to Garrison Keillor and the inhabitants of his make-believe Minnesota village.
Well, times have changed, and so has noise. There’s a lot more of it. And it’s irritating and counter productive. Not just in schools. Noise is one of the biggest complaints in hospitals, and uninvited chatter is one of the reasons open offices fail to thrill everyone who works in them.
Then, too, there are the ubiquitous TV screens that have crept into public spaces—airports, restaurants, doctors’ waiting rooms, hotel lobbies, you name it. They blather on about this or that terrible thing that may befall viewers if they don’t stay tuned to the next story—coming up after this word from the sponsor of the moment. Some call it TV pollution, some call it ambient TV. Never mind what I call it.
Noise, television or otherwise, is not benign. It can cause people to be irritable and anxious—and as a nation we’re irritable and anxious enough as it is. We seem to have grown accustomed to second-hand noise, even though, according to the Environmental Protection Agency, problems related to noise include stress-related illnesses, high blood pressure, speech interference, hearing loss, sleep disruption, and lost productivity.
So why, then, are automakers seemingly conspiring to make automobiles noisier? Perhaps because some cars today are too quiet. Electric cars, and even hybrids, creep up, unnoticed, on unwary pedestrians. Car makers are said to be seeking a solution.
But they’re also trying to make cars noisier in another, one might say dishonest, way. Seems that some drivers still want their rides to sound like muscle cars instead of wimpy sewing machines, and auto makers have taken to supplementing the quiet hum of today’s vehicles with fake engine noises that emulate yesterday’s authentic V8s. They don’t always tell customers the throaty roar isn’t coming entirely from their engines.
Imagine that these sound generators somehow got out of sync, as gizmos often do, and started making engine noises when there should be none? Don’t think it couldn’t happen. It’s a given that electronic gizmos behave badly sooner or later. Chicago’s Union Station, for example, has an automated announcement system that, when I recently passed through said transportation hub, was stuck in a loop, repeating the same nonsensical phrase over and over again. More noise.
Some years ago, someone invented a remote-control device call TV-B-Gone that could turn off televisions in public places. Apparently now there’s an app for that (of course there is). Wonder if it would work on that disembodied Union Station voice?
Somewhere there’s an eighth-grade geek dreaming of inventing a Teacher-B-Gone app. Perhaps he or she already has devised one, judging from the test scores of some students. My advice: Don’t do it, kid. Listen to the 75% of what you can hear your teacher saying. Maybe you’ll learn something interesting and be able to share it in more than 140 characters.
*Kenneth W. Betz, Senior Editor, CBP