ASA PRESSROOM

147th ASA Meeting, New York, NY

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The Missing Leg For A Three-Legged Stool: Why All Benefit From The New National Standard For Classroom Acoustics

David Lubman - dlubman@ix.netcom.com
David Lubman & Associates
Westminster, CA

Peggy Nelson - nelso477@umn.edu
University of Minnesota

Louis Sutherland - lou-sutherland@juno.com
Rancho Palos Verdes,CA

Special Lay-Language Paper for the
75th Anniversary Meeting of the
Acoustical Society of America
May 2004

Together with lighting and ventilation, acoustics is a third essential element of the learning environment in rooms where verbal communication plays such a vital role. While students are assured of adequate school lighting and ventilation by the minimum requirements specified in national building codes, no such codes or national design standards had been developed, until now, for classroom acoustics. Like a three-legged stool missing one leg, this absence of such national standards for classroom acoustics has insured that many of the nation's classrooms fail to provide the vital acoustical environment so necessary for verbal learning. The requirements for low background noise and low reverberation, the two key ingredients of this acoustical environment, were documented more than a half century ago by two renowned educators, architectural acousticians and past presidents of the Acoustical Society of America (ASA), Vern Knudsen and Cyril Harris in their classic book: "Acoustical designing in architecture." This wise guidance has been largely ignored until now.

Full awareness of this "missing leg" in classroom acoustical design finally resurfaced in the 1990s within the American Speech, Language and Hearing Association, (ASHA), ASA and the US Access Board, an independent Federal agency devoted to accessibility for people with disabilities. As a result, in 1997, ASA, working through the American National Standards Institute (ANSI) and with support from the Access Board, established a Working Group to develop the first American national standard for classroom acoustical design. The culmination of that 5 year effort was the ANSI/ASA standard S12.60-2002, Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools. This milestone represents a dedicated effort by the diverse Working Group, the largest ever assembled by ASA, chaired by ASA fellows David Lubman and Louis Sutherland, and strongly supported by the ASA Standards staff. Notable among the many individuals who made special contributions are three no longer with us, acoustical consultant Robin (Buzz) Towne, ASA past-president Robert Apfel and Daniel Johnson, past chair of ASA Committee on Standards.

For "typical" unoccupied classrooms, the standard limits the A-weighted background noise level to 35 decibels (often designated by the symbol, dBA) [See Note (a) for an explanation of the A-weighted measurement scale)]. The other limit in the standard for a "typical size" unoccupied classroom is the reverberation time of 0.6 sec.[See Note (b) for a short description of reverberation)] The standard also defines appropriate noise isolation design requirements for the classroom envelope to limit intrusion of noise from adjacent spaces and the outdoors.

Extensive research was uncovered that supported the need for the standard, including the following:

All children need favorable acoustics for listening and understanding. But children under age 15 are especially vulnerable to poor listening environments because their language development has not yet matured (1).

Schools must meet the listening needs of an estimated 30% of students with disabilities of learning language, behavior, hearing loss, auditory processing, and other special needs. Many special education students will need to be placed in mainstream classrooms in the future. These students have an even stronger need for classrooms that allow clear listening and communication (2).

Many teachers suffer from vocal fatigue in noisy classrooms. In a recent survey (3), 32% of teachers reported voice fatigue, and 20% lost teaching days for that reason.

According to the U.S. General Accounting Office (4), one-third of the nation's schools need major renovation or replacement. Census projections indicate that over 400,000 additional students will enter our schools each year for the next 50 years. This growth means about 16,000 new classrooms are needed each year.

It costs less to design new buildings with good acoustics than it is to fix the problems afterward. For example, noisy heating, ventilating and air-conditioning (HVAC) systems are much easier to quiet in the planning stages than to retrofit with quiet systems at a later time.

Many learning spaces are poor listening places (5) because of:

noise from outside the building, such as from aircraft and traffic;
noise emanating from hallways and adjacent spaces, largely due to the re-emergence of "open plan" school architecture (large rooms lacking ceiling-height partitions between classrooms);
many hard, reflective surfaces in the room and/or high ceilings causing excessive reverberation, without the amelioration of sound absorbing ceilings or wall panels; and
noisy computers, projectors, and other classroom teaching appliances.

There is compelling evidence that children in classrooms require more favorable acoustic conditions than are currently found in most U.S. schools. This research demonstrates that children need:

the target spoken voice to be at least 15 decibels (dB) above the level of the background noise throughout the room,
overall A-weighted sound levels that are no greater than 70 dBA throughout occupied rooms,
background noise that is less than 35 dBA throughout unoccupied classrooms,
sound absorbing materials (in particular, acoustic tiles and panels, appropriately located) that reduce reverberation times to less than 0.6 seconds in unoccupied classrooms.

Evidence shows that learners, especially children, need these conditions for learning because of the following factors:

Young children are ineffective listeners for speech in noise and reverberation until they become about 15 years old., Then they achieve levels of speech understanding similar to those of adults (1).
Children are especially susceptible to ear infections (otitis media) in which middle-ear fluid causes hearing loss that may last for weeks or months.
Many children (up to 20% of the school population) have permanent hearing loss, as a result of congenital, genetic, and environmental causes (6). All people with hearing loss are adversely affected by both background noise and reverberation.
Significant numbers of children are learning in a language not spoken in their home. According to a U.S. Census Bureau report in 1998, 2.5 million school-aged children had limited proficiency in English, comprising between 5 and 11 percent of all school-aged children. In some areas, such as Los Angeles, this percentage is nearly 50%. All people, and in particular, children who are listening in a non-native language are susceptible to interference from background noise (7).
Many children have difficulty remaining attentive to speech in background noise, even though they have normal hearing sensitivity and are learning in their native language (2). These students may have auditory attention and learning problems, and make up an estimated 10-15% of the student body.

The goal of the standard is to optimize the acoustics of classrooms so that a talker located anywhere in a classroom can be understood by all listeners in that room. In classrooms that conform to the ANSI S12.60 standard criteria, normal speech will be heard at a clear signal-to-noise ratio, or SNR, of +15 dB or more (that is, the target speech signal is heard at least 15 dB above the background noise). In those classrooms, nearly all learners, especially children, will have full auditory access to the spoken message.

The challenges to full implementation of the ANSI standard are significant but they are not insurmountable. They fall into the areas of both technology and economics. The HVAC industry in particular recognizes that meeting the requirements of ANSI S12.60 requires careful engineering, selection of materials and proper construction. They also recognize that stringent standards can stimulate innovation. With good noise control design, existing technology can be made to comply with the standard. Key cost considerations include the cost-effectiveness of applying good acoustic design in the beginning instead of having to apply it as a costly retrofit. Secondly, gross estimates of cost benefits clearly show a high benefit-to-cost ratio making good classroom acoustics a wise investment of education dollars. Cost-benefits of good classroom acoustics derive from better educated students, fewer failures and dropouts, increased teacher satisfaction, and lower costs for special education services.

In summary, citing one HVAC industry spokesperson (8):

The body of research substantiating the link between learning and the acoustical character of classrooms is extensive and compelling. Given the vested interest that each of us has in education-whether as a parent, a taxpayer, or an employer-classroom acoustics is sure to receive widespread attention.
It is possible to create quieter classrooms using current technology (design practices, construction materials, and equipment).

The Acoustical Society can be proud of its role in helping bring this challenge to the education infrastructure to the "front of the class." As one of the ANSI Working Group members stated it, "Let the word be heard" (9).

Note (a): The decibel is the logarithmic scale used to describe the physical magnitude of a
sound. A sound 10 decibels louder than another sound has 10 times the intensity of the quieter sound but is perceived, subjectively, as being about twice as loud. The A-weighting approximates how the ear hears sounds of different frequencies or pitches.

Note (b): Reverberation time is the time required for the level of a suddenly interrupted sound - e.g. - the end of a vowel sound in a word - to decay by 60 decibels.

REFERENCES
For general review and information about quiet classrooms, please see the following publications from the ASA:
--Classroom Acoustics I: A resource for creating learning environments with desirable listening conditions, by Benjamin Seep, Robin Glosemeyer, Emily Hulce, Matt Linn, Pamela Aytar and Robert Coffeen, and

--Classroom Acoustics II: Acoustical Barriers to Learning, by Peggy B. Nelson, Sigfrid D. Soli and Anne Seltz

Other references:

1). Johnson, C.E. (2000). Children's phoneme identification in reverberation and noise. Journal of Speech, Language and Hearing Research 43, 144-157.
2). Bradlow, A., Kraus, N. & Hayes, E. (2003) Speaking clearly for children with learning disabilities: sentence perception in noise. J. Spch Lang Hearing Res 46, 80 - 97.
3). Smith E, Lemke J, Taylor M, Kirchner HL, Hoffman H. (1998). Frequency of voice problems among teachers and other occupations. Journal of Voice12, 480-8.
4). U.S. General Accounting Office, Health, Education, and Human Services Division (1995). "Conditions of America's Schools," Document#: GAO/HEHS-95-61, Report # B-259307, February 1.
5). Knecht, H., Nelson, P., Whitelaw, G. and Feth, L. (2002). Structural variables and their relationship to background noise levels and reverberation times in unoccupied classrooms. American Journal of Audiology 11, 65 - 71.
6). Niskar, A.S., Kieszak, S.M., Holmes, A., Esteban, E., Ruben, C. and Brody, D.J. (1998). Prevalence of hearing loss among children 6 to 19 years of age. Journal of the American Medical Association 279(14), 1071-5.
7) Soli, S.D., and Sullivan, J.A. (1997). Factors affecting children's speech communication in classrooms. Journal of the Acoustical Society of America 101, S3070.
8). Guckelburger, D and Bradley, B. "A new standard for classroom acoustics," Trane Engineers Newsletter Vol. 32, No. 1, 2003
9 ) Seltz, A. (2000) personal communication.

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