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Sound decisions improve learning

Constructing or rehabilitating classrooms with acoustic principles in mind can effectively help dampen the noise level, reduce reverberation times and significantly improve speech intelligibility.

Does noise in schools result in lower grades? Sound, lighting and temperature are the three environmental conditions that staff and students notice most often. Since speech is a key element of effective teaching, poor acoustics can have a large effect on learning. In many classrooms, students cannot hear words clearly, and their concentration wanders. Many are straining to hear rather than directing their energy toward understanding the lesson.Nearly all schools have hard materials on walls, ceilings and floors; when sound reflects off these surfaces it leads to high reverberation times and creates disturbing echoes.

Background noise also can be a problem. Sound from outside traffic, adjacent classrooms, corridors or from heating systems creates background noise so loud that teachers have to raise their voices in order to be heard. Combine this with normal levels of noise from children, and it becomes difficult to hear speech.

In a research project in 1996 and 1997, scientists at Heriot-Watt University in Edinburgh, Scotland, highlighted the link between the reverberation times and background noise levels in classrooms. In classrooms with hard surfaces, the percentage of voice consonants lost in the echoes was between 15 percent and 50 percent.

It is also a common belief that noise generates more noise-that is, the poorer the acoustics and the noisier the environment, the louder and noisier the students will become.

There are solutions. Schools can avoid unwanted exterior sounds by situating classrooms more appropriately within the building, isolating walls and slabs, insulating, and minimizing or treating openings. Softer materials, such as fiberglass ceiling tiles or certain types of flooring, absorb sound and reduce classroom noise.

Constructing or rehabilitating classrooms with acoustic principles in mind can effectively help dampen the noise level, reduce reverberation times and significantly improve speech intelligibility.

Keep the noise away

Let's start at the top of a classroom and work our way down:

-The HVAC system. The goal is to isolate noisy HVAC sources from activity spaces. Therefore, classrooms and other areas where students and staff require intense concentration should be kept away from HVAC noise and mechanical rooms.

The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) has established standards and procedures for rating the sound output of mechanical equipment. Consider those when evaluating systems. Also, to limit noise from air-handling systems, consider installing long duct runs, increasing the duct size, lowering the air-flow velocity, installing absorptive fiberglass duct liners or creating noise diffusers or sound traps in the space.

-The ceiling. Acoustic ceiling tiles are an absolute must to control sound. The ceiling is the largest open area in a school where you can control noise. Floors and walls tend to be cluttered with desks, chairs and other furniture, which either create noise or reflect it. Soft surfaces with a little mass, such as fiberglass ceiling tiles, absorb some of the sound and prevent it from being transmitted. Upgrading ceiling tiles will dramatically affect the school's acoustics.

The noise-reduction coefficient (NRC) measures the ability of a substance to absorb sound. Schools should install tile with an NRC of no less than 0.85-that means the tile absorbs 85 percent of the sound that strikes it.

In addition to reducing noise, another characteristic of ceiling tiles to consider is their articulation class (AC). This measures a tile's ability to absorb speech frequencies that strike the ceiling at angles of 25 degrees, a typical level inside a school classroom. An AC rating up to 200 is recommended.

-Lighting. Schools use downlighting most frequently. Uplighting, however, illuminates an area more naturally. It is also more flexible and aesthetically pleasing than putting a luminary directly over someone's desk.

When considering lights, carefully select and place them to minimize noise reflection. Also, keep in mind that dimmers on any type of lighting can actually increase noise levels. Therefore, test these with caution.

In addition, if you select recessed light fixtures, avoid choosing hard plastic lenses or small plastic cubed designs. Select 18- and 24-cell 2-by-4 parabolic units, with individual cell sizes of three inches and eight inches instead to minimize noise.

Absorb, do not reflect -Furniture. Have desks, chairs, work surfaces and other items finished with absorbent treatment to control reverberation. Minimize the use of glass, stone and laminated work surfaces; these reflect sound instead of absorbing it.

-Flooring. Carpeting, rather than tile or wood, improves acoustics. It absorbs airborne sound, reduces surface noise, such as footsteps and furniture movement, and helps block sound transmission to rooms below.

When choosing carpet, insist on ample padding. Thick carpet with an integrated polyurethane cushion cuts noise levels by absorbing sound and reducing its transmission between floors. For example, a concrete floor has a NRC of 0.015, a conventional carpet 0.20, and a polyurethane cushion and carpet 0.25.

Other Tips

Install speakers that transmit a steady level of ambiguous noise into the environment. This will drown out distracting noises, such as conversational speech, from being overheard or understood. A well-designed sound system, mounted above a suspended acoustical ceiling, pointed upward, on 12- to 16-foot centers, will produce an electronically generated, uniform hum similar to the sound made by a school's HVAC system.

Providing this background noise masks the ability of students to hear most distracting noises. These systems typically distribute sound in the neighborhood of 43 decibels, which effectively prohibits normal conversation from being overheard from one work area to the next.

Equipment such as computer printers should be separated, or enclosed within mobile, floor-to-ceiling walls. The goal is to eliminate the line of sight between a noise generator (the machine) and a noise receiver (the student).

Shield work areas and common areas from hard, flat walls and large windows. This can be done with acoustical wall panels placed between the reflective surface and the classroom work area. Otherwise, noise generated in the workstation will bounce directly off the window and into the common area.

Plug leaks between the door and the jamb. Even small openings can allow sound to escape.

By considering good acoustical planning, staff and students will be happier and more productive while teaching, studying and working.

To reduce reverberation time in arts and crafts, shop and science areas, schools should install sound absorbers, such as fiberglass ceiling tiles, to completely cover the ceiling. In these environments, a long reverberation time is a safety risk, because noise could prevent students from hearing warnings and urgent calls. The standard should be a reverberation time of 0.6 seconds. Sound absorbers should be used in walls, too.

In music rooms, or halls where speech alternates with music from a tape recorder, CD or video, the reverberation time should be no longer than 0.6 seconds.

If there is musical instruction using acoustic instruments, it can be an advantage to increase the reverberation time to get more sonorous sound reproduction. Schools can achieve this with the help of special sound absorbers.

In a gymnasium, jumping and running, bouncing balls, verbal encouragement, shouts and whistle signals create high sound levels that make communication difficult. In addition, sound bouncing between the high walls creates a so-called flutter echo.

When teaching is occurring, the reverberation time in a gymnasium or sports hall should not exceed 1.2 seconds. The ceiling surface must be made of a strong material in order to withstand impact,and also should be made of a material that exhibits excellent sound-control properties.

In an auditorium, where speech intelligibility is important, eliminating background sound is the goal. For larger lecture theatres and auditoriums, the reverberation time should not exceed 0.8 seconds. Sound absorbers in the ceiling and in the walls allow speech to be more distinct and background sound less disturbing.

In most classrooms, schools should install sound absorbers in the entire ceiling to reduce the reverberation time and increase the intelligibility of speech. The requirement for hearing speech fully is a short reverberation time-a maximum of 0.6 seconds, and preferably 0.4 to 0.5 seconds.

The school library should be an oasis of peace. Sound absorbers, in the ceiling and on the walls, dampen the sound level and provide quiet for individual studies.

In school cafeterias, for students to converse comfortably, the reverberation time should be reduced to 0.6 seconds.

To accomplish this, install sound absorbers in the ceiling. Curtains, fabrics, furniture and large plants also dampen sound. Or consider dividing the cafeteria into smaller, more inviting areas by using acoustic screens between the tables.

Staff or meeting rooms for teachers require good acoustics. Therefore, the entire ceiling surface should be covered with sound absorbers to reduce the reverberation time to 0.5 seconds.

TAGS: Lighting
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