How to Improve Classroom Acoustics

Acoustical performance is an important consideration in the design of classrooms. Research indicates that levels of background noise and reverberation barely noticed by adults, who are mature and skillful listeners, adversely affects learning environments for young children, who require optimal conditions for hearing and comprehension. Poor classroom acoustics are an additional educational barrier for children who have hearing loss and those who use cochlear implants, since assistive technologies amplify both wanted and unwanted sound. Children who have temporary hearing loss, have speech impairments, or learning disabilities are also significantly affected. Kids who grew up speaking a different language than the teaching language are also at additional risk of educational delay and failure in classrooms that have poor acoustics.

Excessive noise and reverberation interfere with speech intelligibility, resulting in reduced understanding and therefore reduced learning. In many classrooms in the United States, the speech intelligibility rating is 75 percent or less. That means that, in speech intelligibility tests, listeners with normal hearing can understand only 75 percent of the words read from a list.

Although poor sound transmission and long reverberation time (RT) are the main reasons of bad classroom acoustics, there is a cure. Ideally, classrooms should have a sound transmission performance of at least 50 STC and have RTs in the range of 0.4 – 0.6 seconds. However, many existing classrooms have STC in the 40’s and RTs of one second or more. Although longer RTs may be desirable in auditoriums or music rehearsal rooms (and tolerated in gyms and cafeterias) in classrooms they are a hindrance to comprehension and learning.

Classroom Design

Assuming the walls and floors are constructed properly to prevent sound transmission, the best design for a lecture-style classroom would be to move some of the absorption from the ceiling to the walls and keep the middle of the ceiling hard to reflect the teacher’s voice toward the back of the room. Simply place acoustical ceiling tiles around the perimeter of the ceiling and gypsum board panels in the center of the grid.

To reflect more sound to the back of the room, the ceiling can be shaped (angled toward the classroom) over the teacher’s location at the front of the room. This reflecting surface should be built from a hard material like plywood or gypsum board. Placing absorptive materials on the walls simultaneously reduces reverberation time and kills echoes. Fabric-covered, 2 inch thick glass fiber panels are a good choice because they provide some absorption at low frequencies.

If any of the walls are a folding operable type, as is often the case, the operable partition panels should have a good NRC rating and be able to absorb sound. Most folding walls have solid steel and only reflect sound. Skyfold makes a version of their folding wall that has a 0.65 NRC on both sides and provides a 50 STC.

Carpeting on the floors can result in an acoustically superior classroom with a low reverberation time, no echoes, proper distribution of reflections, and low self-noise (foot fall noise). However, don’t put carpeting under a folding / operable wall as it can reduce STC performance.

Entry doors should be positioned as far apart as possible. Also take care to not have doors directly across the hall from two classrooms. Doors with cracks between the door and frame and the typical ¾” undercut allow for considerable sound flanking and distracting noise. With walls of the folding type it is best to  avoid locating a pass through door in it all together as that will greatly reduce the STC performance of the operable partition..

Plan HVAC ducting with sound dampening and/or multiple turns to reduce sound traveling within the ducts from one classroom to another. If walls are constructed with drywall, use drywall of different thicknesses within the same wall, particularly one sheet of 5/8-inch drywall and one sheet of 3/4-inch drywall on either side of the wall. Each thickness absorbs different sound frequencies and their use together prevents transmission of both high and low-pitched sounds.

Nonparallel walls to make the classroom a trapezoidal shape will also reduce echos because this configuration reduces the tendency of sound to reverberate. Ceilings that are higher at the front of the room than the back of the room allow sound to carry to the back of the room without an echo. This helps everyone in the classroom hear the teacher more clearly.

New ANSI Standard

The Acoustical Society of America has taken a hard look at how children react to and perform in different acoustical environments. They offer a wealth of statistics and more importantly simple and cost effective solutions to calculate signal/noise ratios, reverberation times, and noise criteria ratings, which may be necessary to comply with new standards. Their work has been approved by 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, reverberation time, and STC performance for classrooms.

About John Collins

John has over 30 years experience with sales and marketing in the architectural field. He is the owner and operator of RSM Services Inc. a company that provides sales management services in the Northeast USA region and represents Skyfold. If you are a designer from New York, Boston, Philadelphia, Syracuse or Buffalo (and all points in between) and would like to get the straight scoop on operable walls please feel free to touch base.

One Comment

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