Improving Acoustics in Schools
Improving the Classroom Experience Through Acoustics
If a local school board commissions the design and construction of a new school, you can bet it’s because the community needs more classrooms. They wouldn’t be building it otherwise.
So, it’s in the best interest of the dollars allocated for a school construction project, and more importantly the students and faculty, that classroom design be focused on creating an optimal learning environment. If this goal is not forefront in the design process, then the students will likely be stuck with a subpar space and the teachers will have to work that much harder to overcome the poor design. Elements like natural lighting, indoor air quality, high-tech aids and acoustics each affect the physical space of any room. Ultimately, though, it is the built-in acoustics that will have the most profound effect on the learning.
The case for an improved acoustical environment is compelling for every learner and is especially urgent in today’s mainstreamed classrooms where kids with special needs are learning side-by-side their typically developing peers. It is now known that 2.4 million kids are diagnosed with specific learning disabilities1 and up to 8 percent of kids are diagnosed with having ADD/ADHD or Asperger’s Syndrome.2 It is also estimated that at any given time 15 percent of the school-age population suffer temporary hearing loss from ear infections or the common cold.2 In addition, 17 percent of the general population has inherited permanent hearing loss or congenital loss and 12.5 percent have noise-induced hearing loss.3 Also notable is the fact that 10 percent of public school students speak English as their second language.4 Combining these isolated populations into a single, generic classroom paints a sobering picture where special needs might demand the primary design focus.
So are acoustics important in the classroom? You bet. Renowned acoustics consultant and co-chair of the American National Standards Institute committee on noise David Lubman said it best when he stated that we put kids in classrooms where they can’t hear, but we would never put them in a classroom with the lights turned off. Of course we wouldn’t, and we shouldn’t either. Sight and sound are each critical to the process of learning.
Getting Acoustics Right
In order to design classrooms that provide the kind of quiet environment that kids need to learn and teachers teach, there are a few key acoustic concepts to know. Signal-to-noise ratio, perhaps, could be considered Acoustics 101.
In signal-to-noise ratio, the “signal,” which in the classroom setting is likely to be words spoken by the teacher, originates at a certain decibel level. As the signal travels to the back of the room, it dissipates in a predictable manner. Specifically, as the distance the signal travels from the speaker doubles—going from 3 feet to 6 feet to 12 feet and so on—the teacher’s speech level drops by 6 dB per increment until the background noise (typically HVAC noise) around some students is louder than the teacher. In a classroom with typical background noise, academic studies show that only half of what the teacher says can be understood by kids as close as 15 feet away. Kids further away understand even less. This is a pretty poor situation for students, and especially so for those suffering hearing problems or who have learning disabilities. Understanding these implications, the American Speech Language Hearing Association advocates that the signal-to-noise ratio should be no lower than +15 dB which means that at every seat location within the classroom, the teacher’s voice should exceed the HVAC noise level by 15 dB or more.
Primary Source of Noise Pollution
One obvious way to improve the signal-to-noise ratio is to address background noise in the classroom. According to ANSI S12.60-2002, “Acoustical Performance Criteria, Design Requirements and Guidelines for Schools,”the maximum background noise level for a typical classroom that is 10,000 cubic feet (40 feet by 25 feet by 10 feet) or less should be no higher than 35 dB. In 2010, ANSI revised the rule to state that in such classrooms the maximum interior sourced noise level should be no higher than 35 decibels. With this seemingly minor adjustment, ANSI pointed its fingers squarely at HVAC systems. Yes, it is the ubiquitous HVAC systems rattling in schools across the country that are the primary source of background noise in classrooms.
Despite this very clear guideline, HVAC contractors say they are rarely directed to build a noiseless air handling system. Instead, all-to-often they are told to implement systems that handle air in the least expensive way possible. This disconnect between the architect who is designing a quiet classroom and the HVAC contractor designing a cost-efficient system is something that needs to change. ANSI outlines that a single stage HVAC system should be no louder than 35 decibels and a multiple stage or speed system should be no louder than 37 decibels. The technology exists and is cost-effective. Its existence is a direct result of the target noise levels identified by ANSI more than 10 years ago.
In addition to ANSI, the LEED Building Design and Construction for Schools program also takes an earnest approach toward addressing background noise in schools. In its 2007 and 2009 versions, the maximum background noise level for classrooms was set at 45 dB. In the yet-to-be ratified fourth version of LEED for Schools, the maximum background noise level for classrooms is lowered to 40 dB, which is getting closer to ANSI S12.60-2010 allowances.
Sound Absorption Key to Acoustic Design
While noise polluters like HVAC systems need to be addressed in classroom design, so too should sound absorption, which can help prevent reflective noise from becoming a problem. Guidelines offered by LEED for Schools state that for spaces less than 20,000 square feet—which is a large 50-foot by 40-foot by 10-foot room—architects are to specify ceiling panels with a minimum noise reduction coefficient (of 0.70 for 100 percent of the ceiling area (minus the lights and other essential elements). That makes product specification relatively easy since manufacturers readily publish the NRC measurement for the ceiling panels.
To explain NRC, it’s important to understand that noise reduction occurs when materials and objects convert sound into heat energy. Reflected sound always loses some energy, but the amount greatly depends on the material of that surface. This is measured as the NRC. An NRC of 0.00 generally indicates perfect reflection and an NRC of 1.00 generally indicates perfect absorption. So, for acoustic design choose ceiling panels that meet or exceed the 0.70 NRC requirement or opt for a combination of acoustic wall and ceiling panels that equals the ceiling surface area.
To illustrate the impact acoustic ceilings can truly have, just look at a study conducted in 1999 at Heriot Watt University in Scotland. Researchers went into poorly designed classrooms that had no acoustic treatment. Many of the students could understand literally nothing of what the teacher was saying. These were the kids who were sitting in what researchers deemed acoustic black holes. After the rooms were fit with acoustic ceiling panels, every chair met acceptable levels of speech intelligibility. Upon examination of the data, one teacher noted that she thought a particular student was extremely slow until she realized through the study that he could barely understand anything she was teaching solely based on his location in the classroom. What a difference acoustic design and materials can make on the education and life of a student. In this study, the design clearly made a lasting impression on the teacher.
Quiet Classrooms Give Everyone Opportunity to Learn
Architects have the unique ability to influence students’ opportunities to learn through acoustic design. Creating quiet classrooms helps level the playing field among kids of all abilities. It gives kids a fair shot at learning, not to mention teachers a fair shot at teaching. And to do so, it requires a thoughtful approach to background noise and sound absorption. For more information, visit NoNoiseNow.com.
- Learning Disabilities Association of America
- Michel Picard, University of Montreal, 2003
- National Center for Education Statistics
The sound of (not so) silence
Discussing decibels on paper is one thing, but hearing them is another. What does 35 decibels sound like? Consider that 0 dB is the threshold of what a healthy ear can hear. A soft wind is 10 dB. A peaceful apartment in the city is 20 dB. Leaves rustling in the wind hits about 25-35 dB. Typing on a keyboard or having a radio on a low level produces 40 dB of noise, 50 dB is talking in a low voice, 60 dB is the sound of a conversation, and 65 dB is sitting in a small car with the motor idling or normal office noise. Traffic noise generally registers between 75-90 dB.