These days, it's up to school planners more than teachers to keep a classroom quiet. It's tempting to point the finger at unruly students, but other culprits are to blame: walls, ceilings, floors and ductwork. Noise can come from a variety of sources — inside and outside the classroom. It interferes with a student's ability to understand.
Schools often tolerate noisy classrooms. Administrators may believe upgrading is expensive and difficult, or they may not even recognize the problem. Neither has to be the case. Schools can enhance learning by installing acoustic panels and barriers.
Facility planners have several options for restoring quiet to a classroom. The choice of acoustic material will depend on the configuration of the room, what's in it, and how much noise a school needs to cut. The upgrades create quiet places where students can concentrate.
EFFECTS ON STUDENTS AND TEACHERS
Studies indicate that acoustic upgrades should be a priority during classroom renovation. Poor acoustics interferes with speech intelligibility — the ability of a student to hear and correctly interpret instruction or discussion. When a classroom sounds “echoey,” or when outside traffic or noise from the gym class next door interrupts a student's concentration, it's likely that students will miss or misinterpret part of the teacher's lesson. If this happens too often, a student may tune out because it's too much of an effort to listen. As a result, learning suffers.
Students with learning disabilities and hearing impairment are most vulnerable to speech intelligibility problems, but students of all ages and abilities can benefit from better acoustics. Younger students, who are just beginning to learn how to absorb and process words and ideas, benefit especially from quiet classrooms.
Classroom noise affects teachers, too. They may have to speak loudly to overcome background noise and may be less inclined to repeat information. Individual experience varies by classroom, but it's important for school planners to recognize the problem and provide acoustic retrofits.
Washington state and the Los Angeles Unified School District have established standards for classroom acoustics, but national standards for classroom acoustics do not exist. In response to a parent's petition, a workgroup of the Acoustical Society of America and the American National Standards Institute (ANSI) has been developing recommendations for Americans with Disabilities Act guidelines.
The recommendations deal with the two sources of problem noise: background noise and reverberation. According to the ANSI workgroup, ambient noise — noise from all sources — in an unoccupied classroom should register between 30 and 35 dB(A), or about the level of normal conversation. In addition, signal-to-noise ratio (the difference between the decibel level of a teacher's voice and background noise) should be at least 15 decibels.
Reverberation measures how “echoey” the room sounds. The ANSI standard recommends a reverberation time of 0.6 seconds minimum and 0.8 seconds maximum across speech frequencies. In some classrooms, it can take as much as three seconds for a sound to die out. By that time, teachers are well into their next sentences, while the previous words are still bouncing around the classroom. It's easy to see why students may not comprehend what the teacher is saying.
BLOCKING BACKGROUND NOISE
HVAC blowers and breakout noise, caused by air vibrating in metal ductwork, are common sources of background noise. A simple solution to both problems is to install acoustic liners inside the ductwork. Melamine foam is especially suitable for this. It resists fungus and microbial growth, and does not contribute to airborne contaminants.
High-density vinyl barriers within walls can help stop noise from spilling into adjoining rooms. The barrier is most effective when it's installed in a six-inch wall space (most wall spaces are four inches). This provides enough room to stagger the studs by two inches and weave the barrier between the studs.
In classrooms with suspended ceilings, noise can travel between rooms. To reduce this, schools can fasten vinyl barriers to the original ceiling and allow them to hang down to the suspended ceiling panels.
ELIMINATING ECHO (ECHO)
Hard parallel surfaces such as tile, drywall, brick, concrete and glass provide little sound absorption. Normal classroom activity — scraping chairs, opening books, computer motors, group discussion — is amplified in open interior spaces. Carpet and other soft materials provide some sound absorption, but only at frequencies significantly above human speech range. A more effective solution is to install sound-absorbing panels on walls and ceilings.
Acoustic panels provide several advantages. They are lightweight and can be installed easily. A school's maintenance staff could complete the project in a few hours. The panels are easy to install around fixtures and between ceiling rafters and beams.
Installing foam panels on walls or ceilings can preserve the style of classrooms that have tall windows and high ceilings. It circumvents the need for the more expensive alternative of dropped ceilings, remounted light fixtures and smaller windows to reduce a room's size and echo.
The primary consideration in choosing panels is to install ones that are Class 1 fire-rated for flame spread and smoke density.
Johnson is national sales manager for illbruck, Minneapolis, manufacturer of acoustic products for a variety of sound-control applications. illbruck worked on the Shir Hadam Religious School and Farmington projects (see sidebar).
Simple solutions for classroom acoustics
Faced with severe reverberation problems in its classrooms, officials at the Shir Hadash Religious School, Los Gatos, Calif., sought an acoustic solution that would reduce distractions and enhance learning. Converted from retail and office space, the classrooms had 12-foot walls, concrete ceiling beams, tile floors and drywall.
“The classrooms sounded more like warehouses,” says principal Sherri Geeser. “It was hard enough to hear if only one person was speaking; during a group discussion it was impossible to hear.”
Officials tried two different ways to control sound. They put carpet in one classroom, and acoustical foam on the ceiling in another. Officials agreed that the acoustic panels were more effective.
The foam panels, which are Class 1 fire-rated for flame spread and smoke density, reduce reverberation and noise that interfere with sound quality and speech comprehension. The panels were cut and installed by school maintenance crews in less than a day.
In Farmington, Conn, when a sixth-grade band moved into a former art classroom, the band director wasn't too surprised to hear more than just wrong notes. The art room provided space, but it didn't provide the proper acoustics to rehearse a 65-member band, as well as teach music classes and individual lessons. There was so much echo that each note mixed with the next into an acoustic blur.
School officials chose a combination of acoustic panels for the upper walls and acoustic baffles to hang from ceiling girders. The Class 1 fire-rated panels add texture and style to the room, yet are out of students' reach and require no maintenance. School maintenance crews installed the panels and baffles on a Saturday, and on the following Monday, the rehearsal sounded like an actual band.