Reducing Classroom Noise
Based on computer simulations, tests in schools and experiments with a scale model of a classroom, the recommendations come as the federal government moves toward setting a limit on classroom noise under the Americans with Disabilities Act. "We've come up with where to place acoustic material in rooms, how much should be used, what types of a/c systems cause the least noise and other variables, such as the preferred shape of the room," said Gary Siebein, a UF professor of architecture and researcher on classroom acoustics.
Siebein recently presented his findings at the Acoustical Society of America meeting in Fort Lauderdale, FL. Research over the past several years by Siebein and Carl Crandell, a UF professor of communications sciences and disorders, has revealed that noisy classrooms seriously impil1ge on many students' ability to learn.
In visits to 47 Florida elementary, middle and high schools, the researchers discovered the majority had background noise levels of between 40 and 55 dB. Thirty dB is nearly inaudible, while a normal speaking voice registers at about 60 dB. The noise in schools most often came from air conditioning units, which have become increasingly common in schools as the population in the Southeast has ballooned, Siebein noted.
People generally complain about having a hard time hearing once background noise reaches 50 dB, Siebein said. Crandell's research showed that students seated more than 12 ft away from the teacher in the noisy classrooms heard 50% or less of the lecture. Given the common placement of desks in rows, that often meant that more than half of the students were not hearing everything the teacher had to say, he concluded. The problem worsened when related factors were considered.
Crandell found, for example, that between 10% and 30% of students have some kinds of moderate or mild hearing loss caused by scarring from ear infections, for example. Noisy classrooms exacerbate these students' listening challenges. Students learning English as a second language and students suffering from Attention Deficit Disorder or other attention problems, also hear less in noisy classrooms.
The findings, which dovetailed with the conclusions of other experts nationwide, sparked involvement by the Federal Access Board, which creates regulations under the Americans With Disabilities Act. A committee of the board looked at the data and, in June, recommended a noise standard of 35 dB and 0.6-second reverberation. Reverberation is defined as the length of time a sound remains in a room after the noise stops. The standard is now under review. But in 2003, when it is expected to go into effect, architects and building contractors will need to know how to meet the requirements. That's where Siebein's latest work comes into play.
Siebein said his research is based on noise measurements in numerous real-life classrooms as well as tests in the one-quarter- scale model classroom, which is complete with miniature chairs and desks. He and his graduate students plugged data collected from these sources into a computer program originally designed for concert halls. The resulting "virtual classroom" allowed testing of classroom shapes, sound conditions and construction materials.
The researchers' strongest conclusions involved air- conditioning systems. They found that wall- or window-mounted air-conditioning units and heat pump or fan/coil units made noise that consistently exceeded the 35 dB. Only central air- conditioning writs were quiet enough for the standard.
Although it will apply only to new schools, the number of aged schools and portable classrooms means many students will continue to be subjected to too much noise, Siebein noted. The researchers found students hear better in square rooms with ceilings less than 10 ft high than in rectangular rooms or irregularly shaped rooms with higher ceilings.
They also found that total absorbent material should equal total area for maximum noise reduction. For example, a 900-sq-ft room should have 900 sq ft of acoustical ceiling tiles or wall panels.
"Our information will help people decide, 'What can we do? What are the costs? Is there a premium in terms of added material for this or that design?'" Siebein said.