THE SOUNDS OF A SOUND EDUCATION
- By Michael Fickes
- June 1st, 2003
East Boston High School recently shushed Boston’s Logan Airport with sound-resistant windows. Other schools around the country have been discovering the educational benefits of amplifying the voices of classroom speakers. Still others are beginning to apply long-standing advice from acoustical designers in their music suites.
Schools today are working harder than ever to keep the distracting sounds outside and the educational sounds inside, thanks to research that shows how important it is for students to hear what is going on.
Of course, everyone knows that students must hear their teachers. But the latest research suggests that conventional acoustical techniques may not do enough to ensure that students can hear what’s going on. A National Geographic article (Sounds Dangerous, July 2002) reports that students attending schools near airports perform worse than students from quieter schools. Other studies show that performance improves with classroom amplification systems.
Turning Up the Teacher’s Voice
Across distance, you lose speech, says Jeff Anderson, vice president with Audio Enhancement, a Salt Lake City firm that provides classroom amplification systems.You don’t just lose volume; every time the distance between a speaker and an audience is doubled, listeners lose the clarity of speech. In a classroom, the kids in the front row are fine, as long as the teacher doesn’t move around or turn to the blackboard. But the rest of the class suffers from this distance problem.
Audio Enhancement calculates that a teacher’s voice should always sound like it is no more than eight to 10 ft. away from every student. To create that effect, the company has patented an infrared amplification system that places speakers in classroom ceilings and equips teachers with wireless microphones.
Earlier systems employed FM radio transmission and suffered from interference from other radio signals. Infrared transmission, however, uses invisible light waves to transmit voice signals to an amplifier the size of a DVR located somewhere in the classroom. The amplifier then sends boosted signals across wires to the speakers. Infrared light transmission eliminates the problem of interference because infrared light cannot pass through walls.
Audio Enhancement systems include two microphones to facilitate team teaching or to allow students to pass one of the microphones around the room — so students can hear each other talk.
Some school districts have begun to require classroom amplification. The state of Ohio recently mandated amplification in all K-5 public school classrooms. Orange County, Fla., requires amplification in K-12 classrooms. According to Anderson, about 5,000 schools across the country have installed amplification systems, with deployments doubling through the past three years.
The effect of amplification systems has been studied exhaustively in recent years. Within a year of installing a system, students at Maple Grove Elementary School in Golden, Colo., improved their performance in formal assessments by
3.6 percent. At Pioneer Elementary School in Salt Lake County, Utah, students for whom English is a second language achieved an average reading comprehension improvement of 16.25 percent on state required Criterion Reference Tests.
Recent Brigham Young research suggests that students who cannot hear what teachers say lose both the desire and the ability to learn. In this study, audio-enhanced classrooms raised student test scores by four percent to 15 percent.
Another Brigham Young study discovered that teachers perform better with sound enhancement systems. In a 2002 study of six school districts with classroom amplification systems, teacher absenteeism decreased by 30 percent. During the 1994-1995 school year, Dubuque, Iowa, public elementary school teachers called in sick 60 percent less, saving $2,500 in substitute teacher costs.
Building Sound Barriers
Built in 1924, the landmark East Boston High School building overlooks the glide path into Logan Airport, and incoming flights had been making teeth chatter, inside and outside the building, for years. No more. A renovation has replaced 362 double-hung windows and transoms with double-hung and double-sash acoustical windows made by Graham Architectural Products, Inc., of York, Pa. Arched, sound-insulating windows also protect the school’s gymnasium from the roaring jets and illustrate the custom capabilities of sound-resisting windows.
Designed to form a sound barrier strong enough to reject all the jet noise, the dual or double windows at East Boston feature a common approach to keeping sound out: two walls of heavy mass separated by an airspace.Separating walls of heavy mass — glass — with a few inches of air space provides a big improvement in acoustical performance, says Bill Wilder, manager of technical services with Graham.
Does insulated glass provide an acoustical benefit? Yes, says Wilder. Insulated glass can improve acoustical performance in a traditional window. But the most cost effective sound barriers use a single pane of glass outside and single pane inside, separated by a couple inches of air. Thicker glass can also improve soundproofing performance. In Chicago’s public schools, for example, Graham installed one-in.-thick insulated glass with two 3/16-in. panes separated by a 5/8-in. airspace. The design keeps the sounds of the city’s elevated trains from rumbling into classrooms.
East Boston’s new windows boast a sound transmission class or STC rating of 45, which is very high (and very good) for a window. Conventional windows in homes are generally rated in the low to mid 20s, says Wilder. Commercial buildings with one-in.-thick panes of insulated glass have STC ratings in the mid 30s.
Not all schools need acoustical windows. Schools near airports, in urban settings and locations near interstate highways, however, may benefit from acoustical sound barriers, says Bill Martin, director of sales and marketing with Graham. Sometimes a school will only need acoustical glazing on one side, continues Martin. Suppose one side of a school faces an interstate highway; one side of acoustical windows may be sufficient.
At least some acoustical principles inform the design of every music room. The goal is to keep unwanted sounds out, while enabling musicians inside music rooms to hear a full range of musical tones, from the loudest to the softest, the lowest to highest.
The Wenger Corporation of Owatonna, Minn., pushes its school customers to exceed merely adequate design in these spaces. Wenger supplies interiors for performing arts suites and consults, with a music lover’s passion, on the finer points of acoustical design. A music space is unique, says Michael Smedstad, vice president of new business development with Wenger. Music learning comes from a form of critical listening that makes great demands on students and teachers. You listen to a wider range of frequencies, from very low pitches to very high pitches. Some frequencies are beyond the range of hearing but still add color to musical sound. So the frequency range and the dynamic or loudness range necessary in a music facility is much different than in a normal classroom.
Four design concerns affect music suites: the volume; isolating music rooms from other sounds and each other; the shape of a room as well as the wall, ceiling and floor treatments that control musical sounds; and controlling noise from a building’s mechanical systems.
As a rule of thumb, Smedstad recommends that band rehearsal rooms be a minimum of 2,500 sq. ft., large enough for an average-sized school band with 60 to 70 members. Choirs with 60 to 80 members need at least 1,800 sq. ft. Ceilings should rise 18 to 22 ft. Smaller bands and choirs do not imply smaller rooms. Undersized rooms can impair a musician’s hearing. Sixty instruments are not twice as loud as 30 instruments, Smedstad says. Loudness builds gradually, and rooms need to be large enough to dissipate high sound levels.
Rooms that are too small hamper critical listening. According to Wenger research, a 2,500-sq.-ft. room with 20-ft.-high ceilings delays the reflection of sound within the room by 20 milliseconds. Shorter reflection times, produced by smaller rooms, make it difficult to hear the music clearly enough to make musical judgments.
Music suites often contain rehearsal rooms for both bands and choirs. Designers try to isolate these rooms and prevent sounds from one from penetrating the other. According to Wenger, choir and band rooms often stand side by side, with a single wall separating the two. It is expensive to build a wall to stop low-frequency band sounds from penetrating adjacent rooms, says Smedstad, who suggests creating a buffer zone between rooms.
The buffer zone idea affects the layout of the music suite. Most suites require offices, storage rooms and other ancillary spaces. Why not lay out the suite with these rooms separating the rehearsal rooms?
A corridor of offices and storerooms can create a large buffer zone with three walls and two air spaces. This is terrifically effective in stopping sound, Smedstad says.
Conventional wisdom suggests that music room shapes should avoid parallel walls that create echoes and unwanted acoustical anomalies. But designing a room with curved and cornered walls capable of controlling anomalies usually costs too much. We think the lowly rectangle is the best way to spend your dollar, Smedstad says. You eliminate the extreme costs of exotic shapes, and you can come back with acoustic diffuser and absorber panels to correct anomalies. In fact, an odd-shaped room will still require diffuser and absorber panels.
Eighty students making music in a band room will work up a sweat.
To maintain a comfortable environment, air exchange rates must double, according to Smedstad. But this raises the noise level of the air conditioning system. The trick here is to enlarge the grillwork and ductwork so the air flows slowly into the room, he says. In addition, absorptive lines are usually installed inside the ducts.
Today, acoustical considerations can improve the performance of virtually every component of school building design. Exterior design can prevent noise pollution from getting inside a building. Classroom technology can amplify the teacher’s voice. Music rooms can protect hearing and enhance performances. Taken together, all of these sound design techniques can make the music of education more beautiful.