The Sound of Learning
- By Amy Milshtein
- March 1st, 2007
Would you tolerate textbooks with every fourth word missing? Outrageous as it sounds, that’s the acoustical condition in many of today’s classrooms. According to Classroom Acoustics, a publication of the technical committee on architectural acoustics of the Acoustical Society of America, speech intelligibility among listeners with normal hearing is about 75 percent or less in many of today’s classrooms. This means that listeners miss one out of four words read to them off a list. Adults and older children can use their experience tofill in the gaps and make sense of what’s being said. Younger children who are just exploring language, ESL students, the learning disabled, and the hard of hearing do not have that luxury.
That number of hard-of-hearing students is remarkably large and flexible. The Centers for Disease Control and Prevention estimates that up to 15 percent of school-age children suffer from temporary hearing loss at any time. Allergies, ear infections, and colds or other forms of congestion mean that today’s competent hearer could be tomorrow’s hard-of-hearing student.
The good news is that making classrooms acoustically sound is neither difficult nor expensive. A bit of forethought, a small upgrade in materials, and acoustical enhancement is all it takes to make classrooms and other core learning spaces better.The best way to solve acoustics problems is to prevent them beforehand, not correct them after the fact, continues the publication. Renovation of poorly designed classrooms is much more expensive.
Thankfully, more and more states are implementing ANSI/ASA S12.60-2002, Acoustical Performance Criteria, Design Requirements and Guidelines for Schools. Consistent with long-standing recommendations for good practice in educational settings, the new standard sets maximum limits for background noise (35 decibels) and reverberation time (0.6 to 0.7 seconds) for unoccupied classrooms. New Hampshire State Board of Education, New Jersey School Construction Board, Ohio School Facility Commission, Minnesota, and Connecticut have all adopted this standard. Areas like New York State, Los Angeles Unified, Washington State, Washington DC, and others have similar standards and directives in use.
One may be surprised, however, to know how many remaining school districts prioritize acoustics below landscaping. Don’t laugh, insists Bennett Brooks, PE, FASA, Brooks Acoustics Corporation and co-author of the ANSI/ASA code. I’ve heard of school districts saving money on ductwork so they can plant better bushes. The biggest problem with acoustics is you can’t see or touch it.
I’ve been designing schools for 35 years, and in the beginning, acoustics weren’t on the table, says Michael Hall, AIA, chief marketing officer, Fanning/Howey Associates, Inc. Noisy air handling equipment went in the classroom or in a room right next door. In the last 10 years, the attitude has changed. When LEED for school design (a recommendation on how architects can design ‘green’) comes out, it will include a section on acoustical standards urging designers to meet the Reverberation Time and Impact Insulation Class sections of the ANSI Standard.
In fact, contemporary energy-saving practices solve many acoustics problems right off the bat. Double insulated glass windows, thicker exterior walls, and better fitting doors and windows buy acoustical benefits, says Lois Thibault, architect and research coordinator for the US Access Board. Thibault goes on to warn that, materials chosen for ease of maintenance, like hard tile floors and wall treatments, could make acoustics worse.
To keep the reverb caused by hard surfaces down, one only has to look up. Ceiling tiles with a Noise Reduction Coefficient of .85 or .90 will improve acoustics dramatically, says Brooks who explains that this rating means that 85 to 90 percent of the sound will stick to the tile, allowing the rest of the sound to bounce back. Buying good acoustic ceiling tiles will not put a huge dent in the budget. Ineffective ceiling tile runs about 20 cents a square foot, says Tom Roger, Gilbane. Effective tile is 80 cents.
Larger rooms like gymnasiums, cafeterias, and auditoriums need different treatments. Their tall ceilings and hard surfaces make for highly reverberant spaces than can be uncomfortable to work in. I’ve seen gyms that had four- and five-second reverberation times, recalls Brooks, That’s too noisy and unsafe. We try to get these spaces down to one-second reverb time.
As high ceilings do not benefit from acoustical tiles, professionals bring the reverb time down with soft wall treatments. The same standards should be met with auditoriums and cafeterias. Cafetoriums, a blended space common in elementary schools, should also be treated with acoustical sensitivity. Absorptive metal decks in the roof systems solve a lot of problems, says Hall.
Step Up to the Mic
Technology in the classroom can make good acoustics better and moderate listeners more attentive. Sound fields or audio enhancements hook the teacher up to a wireless microphone. Speakers set in quadrants around the room bring the teacher’s voice closer to the students. Just like you wouldn’t have one light pointed at the front of the class and just teach during the day, you shouldn’t have just one voice projecting out, explains Jeff Anderson, president, Audio Enhancement.
A standard 900 sq. ft. classroom would have four speakers positioned in the space. The teacher wears one microphone on a neck loop. Another microphone would be passed around by the students who want to talk. Infrared technology keeps everything wireless. The kids can’t wait to participate with that microphone, says Anderson. Even shy children come out of their shells when it’s their turn.
Inexpensive (around $1,000 a classroom) and easy to install (about a half an hour from start to finish), systems like these require no training to use. However, they don’t solve every problem. This is not a substitute for good acoustics, says John Merline, marketing director, Front Row for Active Learning. If your room has a reverb problem this kind of product might make it worse.
Brooks agrees. You have to be very careful if you put a sound system in a classroom. In a room that is acoustically bad, the system can produce sound levels that are uncomfortable and even hazardous. If you apply the 15-dB-signal-to-noise ratio (S/N) for good speech intelligibility, and have a background noise from the heating / air conditioning system of 70 dBA (like a vacuum cleaner — as I have measured in some school rooms), then the resulting sound level will be 85 dBA (70 + 15 = 85). If you use the typically recommended S/N for public address system design of 25 dB, then the situation would be even worse.
Others feel that most classrooms would benefit from the technology. I estimate that there are only one percent of classrooms in the country that are so reverberant that they wouldn’t get some benefit from the system, insists Anderson.
Not to mention the advantages teachers gain. We’ve seen studies that show teacher absenteeism drops 30 percent after an audio enhancement system has been installed, says Anderson. Instructors never have to raise their voices so they don’t suffer a strain. Everyone feels calmer and safer. Teachers also leave class less tired each day. Anderson points to studies suggesting student benefits as well. Kids scored higher on spelling tests because they could actually hear the consonant sounds better, he says. When you raise your voice it’s the vowel sounds that are louder.
The technology allows AV equipment to be hooked up to the system as well. New advancements allow teachers to control the volume of both mics from their unit. This keeps the class moving by empowering the teacher to make adjustments quickly, explains Anderson.
Once a school tries one of the systems, the benefits become clear and profound, says Merline. As such, audio enhancement products are now required in Ohio; Ann Arbor, MI; Seattle; and districts in Florida and Texas. I think these products work wonderfully, says David Ferguson, senior project architect, owner, ZMM. When the budget allows it, I always include it in the design for every grade from kindergarten through high school.