September 21, 2010 Audiology

Classroom Acoustics: What Possibly Could Be New?

Many audiologists and speech-language pathologists work with children, and we know that a child's ability to hear and listen is very different from that of an adult. When it comes to designing schools, however, not everyone seems to understand the implications of this difference.

Many architects and designers simply are not aware that children develop their ability to understand speech over time, and may create a school that is "good enough" for adult listening but inadequate for children. Audiologists and SLPs must be the advocates for children in school design and insist that classrooms be designed with children's developmental needs in mind.

ASHA has been actively involved for more than 15 years in the development of standards for school acoustics. In 1997 a family filed a complaint with the U.S. Department of Justice claiming the local school was just too noisy for their child, who had a hearing loss, to have appropriate access to spoken information. ASHA got involved, as did the U.S. Access Board, an independent federal agency devoted to accessibility for people with disabilities. Around the same time, the Los Angeles Unified School District invested in room air conditioners that sometimes pumped 65 dB of sound into the room, and teachers and students pressed for quieter solutions. A flurry of activity resulted that continued a long tradition of advocacy by ASHA and other organizations (see "Classroom Acoustics Standard Timeline" [PDF] for a timeline of classroom acoustics activities). 

Noise in classrooms is unwanted sound that is usually caused by heating, ventilating, and air-conditioning equipment (HVAC), noise from outside the building leaking through windows and doors, and noise from adjacent rooms and hallways coming through walls and doors. Reverberation is the persistence of sound after its source quiets and arises from sound reflecting from hard walls, floors, and ceilings. Reverberation time (RT60) is defined as the length of time in seconds required for the sound level to reduce by 60 dB once the sound source has been turned off.

American National Standard 

So what's really new? Significant progress has been made recently in classroom acoustics standards development. The American National Standards Institute (ANSI), which oversees the creation, promulgation, and use of thousands of standards and guidelines, recently revised and reissued the American National Standard addressing classroom acoustics (see next page). The standard, like all American National Standards, is voluntary, and becomes mandatory only if the standard is incorporated into laws such as building codes.

Unfortunately, the International Code Council (ICC), which develops codes and standards used to construct homes and schools, rejected a proposal to reference the new ANSI standards in its revised building code at its May meeting (see The ASHA Leader, Aug. 3, 2010). This rejection is significant because many state and local governments adopt the International Building Code in their municipal building codes, a move that turns the voluntary guidelines into law. The next opportunity to revise the International Building Code is in 2015.

Two months after this setback, the effort to require compliance with the standards shifted to the regulatory tract. The policy board of the U.S. Access Board, which is charged with developing accessibility guidelines for the Americans with Disabilities Act and Architectural Barriers Act, voted unanimously to include a reference to the new classroom acoustics standards in guidelines for both acts. If the standards become part of the rules, any entity accepting federal funding—including all public and some private schools—would be required to comply. 

Although the Access Board indicated that the classroom acoustics rulemaking will be placed on a fast track, the rulemaking process can take up to several years. The process involves development of the rule and cost-benefit analysis, review by the U.S. Office of Management and Budget (OMB), publication of the proposed rule in the Federal Register, a period for public comment and public hearings, revisions based on public feedback, resubmission to OMB for review, and publication of the final rule in the Federal Register.

Revised Classroom Standards 

The American National Standard addressing classroom acoustics was first published by the Acoustical Society of America (ASA) in 2002. The new ANSI standards include several changes:

  • The standard was revised in the form of a series of documents. The original standard with some modifications became Part 1 of the series and is limited to permanent buildings (ANSI/ASA S12.60-2010/Part 1; American National Standard Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools—Part 1: Permanent Schools).
  • A new part of the standard was developed to address the specific issues related to relocatable classrooms (ANSI/ASA S12.60-2009/Part 2; American National Standard Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools—Part 2: Relocatable Classroom Factors).
  • Both Parts 1 and 2 were written to be "code-friendly" (suitable for reference in building codes). As part of this process, most of the informative elements of the standard were removed and are intended to be collected into a new part.
  • The measurement procedure was simplified and clarified. The noise contributions from interior sources (e.g., HVAC, lighting, plumbing) and exterior sources (e.g., traffic, airplanes, railroads) are measured and evaluated separately.
  • HVAC noise was clarified as being an hourly average value; some metrics used for measurement of sound transmission from outside to inside were changed; and classroom audio distribution/amplification systems requirements were added.
  • The well-known major requirements of the standards for permanent structures remain essentially unchanged: The greatest one-hour average A-weighted background sound level in a furnished but unoccupied classroom shall not exceed 35 dB; the C-weighted background sound shall not exceed 55 dB; and for most average-size classrooms the RT shall not exceed 0.6 second.
  • For relocatable structures, the standard provides a timed phase-in of the 35 dB requirement to
    allow for engineering changes that need to be implemented to achieve the goal. The RT requirement for average-size relocatable classrooms is a bit lower (0.5 second) because these buildings generally have lower ceilings.

Parts 1 and 2 of ANSI/ASA S12.60 can be obtained at no charge at the Acoustical Society of America's website. Part 3, under development, will address the control of noise from information technology equipment in classrooms.

Classroom Amplification 

Why must we make rooms quieter—why not just make the teachers' voices louder? The use of microphones, amplifiers, and speakers in classrooms has become popular in recent years, and many children with auditory disorders need personal amplification. Customized use of FM or infrared amplification systems can help many students and teachers. With these systems, the signal level is greatly improved because only the voice at the microphone, not the background noise, is amplified (see Crandell & Smaldino, 2001, or Nelson, 2000, for a detailed explanation).

However, amplification systems are only a partial solution. Much of classroom learning is peer-based and active, and the teacher frequently serves as a guide to group discussions rather than a lecturer. In group activities the signal source changes frequently—one moment it may be a teacher, a child the next moment, followed by a multimedia presentation. Although amplification systems are an important component for children who need higher signal levels, reduction of background noise and reverberation is necessary to ensure that each child has full access to learning.

Today virtually every new or renovated classroom will be equipped with an audio distribution system, not only to amplify the teacher's voice but also to enable the presentation of multimedia content. Part 1 of the new ANSI/ASA standard includes requirements to address the potential problems caused by amplified sound from adjacent classrooms leaking into a classroom. This requirement is not an endorsement of the wholesale use of sound reinforcement in acoustically deficient rooms. Carefully designed audio distribution systems can be an important tool in a room with good acoustics but can never be the only solution for poor acoustics in classrooms. The standards continue to emphasize that only quiet classrooms with low reverberation allow universal access to important classroom communication.

Next Steps 

In 2010 we have excellent standards—but they are not obligatory and only a few states and districts have adopted them for new building construction (a list of states and school districts that have adopted the standards is available at the United States Access Board's website. ASHA and other organizations continue to advocate for improved classroom acoustics by getting those standards into practice. The literature supporting the standards is incontrovertible, and includes the following information:

1. All children need good acoustics to understand familiar words and learn new information.

A great deal of research has shown that noise and reverberation adversely affect typical young children more than they affect typical adults. For example, Werner and Boike (2001) have shown that typically developing infants are immature listeners who don't easily separate signals from background noise. Stelmachowicz et al. (2000) demonstrated that 5-year-olds can repeat fully audible words and sentences in quiet as well as adults; however, when the audibility of the words is reduced to 50% (still very easy for adults), children cannot understand most of what is said.

Children develop their ability to understand in noisy and reverberant conditions (e.g., Johnson, 2000) throughout their early years and mature during adolescence. Soli and Sullivan (1997) showed that adults can understand most familiar words when the noise level and the speech level (or the signal level) are approximately equal (i.e., the signal-to-noise ratio is approximately zero). However, typical children younger than 13 years need background noise levels that are significantly quieter than the signal they are trying to hear. The evidence clearly indicates that even typically developing children don't hear as well as adults until well into adolescence. Auralizations of these differences done by Nelson, Sacks, and Hinckley (2009) can be heard online at the lab's web site.

2. Children who have hearing loss, are learning in a second language, or have auditory or attention problems need even more favorable acoustics. 

Auditory learning problems are quite prevalent among school children (ASHA, 2005); in addition, there are many children with hearing loss. Some estimates suggest that at any given time, up to 25% of young children have ear infections and others may have slight hearing losses due to more permanent conditions (Bess, 1998; Niskar et al., 2001). Children with hearing loss are significantly affected by background noise. They require lower background noise levels and higher signal levels for understanding than do children who hear well (Crandell, 1993; ASA, 2003).

Many school districts have large numbers of children who speak languages other than English at home. According to a 2000 U.S. Census Bureau report, 20% of all school-aged children (about 10 million) who spoke languages other than English at home had limited proficiency in English. Across the United States, major metropolitan areas are reporting that 40% or more of their students speak languages other than English at home (U.S. Census, 2000). In the early grades, 50% of children in the Los Angeles Unified School District speak other languages at home.

All people listening in a non-native language are more susceptible to background noise (e.g., Mayo, Florentine, & Buus, 1997). Children who are learning English as a second language are especially affected by classroom noise and need quiet rooms to understand their teachers and English-speaking peers. Nelson, Kohnert, Shaw, and Sabur (2005) demonstrated that two groups of second-grade children (those whose first language was Spanish and those who spoke only English) performed equally well on English word understanding in quiet. However, the Spanish-language children performed significantly more poorly than English-speaking children for word understanding in noise at +10 dB SNR. In our increasingly diverse nation, multilingual families will become more common everywhere and children from those families will need favorable acoustic conditions.

In addition, estimates suggest that 5% or more of all school children have learning disorders or attention deficit/hyperactivity disorder (ADHD), a neurobiological condition that affects the child's ability to maintain attention (ASHA, 2002). Poor acoustic conditions cause increased distractibility, reduced attention, and increased impulsivity among children with ADHD (e.g., Breier, Gray, Klass, Fletcher, & Foorman, 2002).

It is clear that in all schools there are children with special needs who require favorable acoustics to pay attention, to understand, and to learn.

3. Classrooms are frequently too noisy for learning, but we have the technology to make quiet classrooms.  

The most significant noise source in many classrooms is the HVAC system. In some schools, the HVAC system projects 65 dB into the center of the room, the same level as the teacher's voice at a distance of one meter. Children in those rooms who sit farther than one meter from the teacher (and it is obvious that many children do) can hear the HVAC noise better than they can hear the teacher. Some teachers told the ANSI/ASA working group that revised the classroom acoustics standards that they alternate between talking (teaching) and cooling the room because they simply cannot raise their voices above this intrusive noise.

Knecht, Nelson, Whitelaw, and Feth (2002) measured reverberation and background noise levels in 32 unoccupied elementary classrooms in eight public school buildings in central Ohio. Background noise levels ranged from 32 to 67 dB. The noisiest classrooms were those with noisy HVAC units, causing an additional 10–15 dB of noise in some areas.

The good news is that the HVAC industry has been working to improve its products and, with planning, most HVAC noise problems can be avoided or resolved. In the past, the HVAC industry was an outspoken opponent of the criteria in ANSI/ASA S12.60-2002. But that opposition changed when the new standards were submitted to ANSI-Accredited Standards Committee S12 for approval; the Air-Conditioning, Heating and Refrigeration Institute supported the new standards although the criteria were essentially the same.

4. Reverberation complicates the noise problem.

Excessive reverberation "smears" the temporal properties of speech signals when reverberation times (RT60s) exceed about 0.6 seconds. RT60 measurements for the 32 classrooms in the Knecht et al. study (2002) ranged from 0.2 to 1.27 seconds. Because of the combination of the observed noise levels (32 to 67 dB) and RTs, teachers' voices are often reaching students at unacceptably low signal-to-noise ratios with excessive reverberation.

5. Teachers sometimes suffer the most.

Evidence shows that noisy classrooms require teachers to speak at vocal levels that cause vocal stress and fatigue (e.g., Smith et al., 1998). Many teachers complain of tired voices, vocal strain, and health concerns caused by their need to speak so loudly. In quieter classrooms, teachers can speak at more comfortable levels and their voices can still be heard throughout the room.

Grassroots Advocacy 

All children—those who are developing typically and those who have special needs—have acoustical requirements. Acoustical controls should be in place so that children reach their full potential to hear in their classrooms, in the same way that lighting allows children to see well and HVAC systems allow them to be comfortable.

Important progress has recently been made in classroom acoustics standards development, and the next critical step is the adoption of those standards by those who build and remodel schools. Our collective efforts are extremely important and still necessary; even in this challenging economy, new schools are being built and remodeled, some with federal stimulus money. Despite the recent setback from the ICC, discussions will be happening at the local and national levels, where each of us can be an advocate for children in the schools. In addition, school audiologists and SLPs can work to ensure that classroom audio distribution/amplification systems are used appropriately and are not seen as the cure-all for a room with poor acoustics.

Audiologists and SLPs can become involved in efforts to ensure good classroom acoustics. They can:

  • Get involved early in the process when new schools are being planned. Bring the standards and the Americans With Disabilities Act Notice of Proposed Rulemaking to the attention of the building planners. Make presentations to the school board before decisions are made.
  • When classroom amplification systems are requested for multimedia use or for aiding teachers' voices, help make good decisions and ensure the systems are installed appropriately and wisely.
  • When amplification systems are proposed as solutions for noisy HVAC or poor-quality doors and windows, encourage the school to solve the noise problem at the source.

Teachers, parents, educators, and speech-language and hearing professionals all can help ensure that rooms designed for learning meet children's unique needs for seating, lighting, comfort, and sound.  

Peggy B. Nelson, PhD, CCC-A , is an associate professor in the Department of Speech-Language-Hearing Sciences at the University of Minnesota. A member of the Acoustical Society of America's Task Force on Classroom Acoustics, she testified before the ICC on the new ANSI/ASA standards in June. Contact her at

Susan B. Blaeser, the standards manager at the Acoustical Society of America, administers the development of national and international standards on acoustics, bioacoustics, mechanical vibration, and shock and noise. The ASA Standards Division involves more than 500 volunteers. Contact her at

cite as: Nelson, P. B.  & Blaeser, S. B. (2010, September 21). Classroom Acoustics: What Possibly Could Be New?. The ASHA Leader.

Classroom Acoustics Resources

ASHA Classroom Acoustics Webpage 

ASHA's classroom acoustics webpage includes links to a number of resources for audiologists and classroom teachers:

  • ASHA Practice Policy Documents—

Acoustics in Educational Settings (position statement and technical report)

Appropriate School Facilities for Students With Speech-Language-Hearing Disorders (technical report)

Guidelines for Addressing Acoustics in Educational Settings

Guidelines for Audiology Service Provision in and for Schools

  • ANSI StandardAmerican National Standard Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools (Part 1 and Part 2)
  • Journal articles on classroom acoustics
  • Related linksFacebook and Yahoo groups; Healthy Youth! (CDC webpage on noise-induced hearing loss); National Clearinghouse for Educational Facilities; Northern Illinois University web module to educate teachers about classroom acoustics; Quiet Classrooms Noise Pollution Clearinghouse; Institute for Enhanced Classroom Hearing

Additional Resources 


Acoustical Society of America (2002). Classroom acoustics: A resource for creating learning environments with desirable listening conditions.  

Acoustical Society of America (2002). Classroom acoustics II: Acoustical barriers to learnings [PDF].

American Speech-Language-Hearing Association (2002). Attention Deficit/Hyperactivity Disorder (ADHD).  

American Speech-Language-Hearing Association (2005). The prevalence and incidence of hearing loss in children. Audiology Information Series[PDF]. 

Bess, F. H., Dodd-Murphy, J., & Parker, R.A. (1998). Children with minimal sensorineural hearing loss. Ear and Hearing, 19, 339–354.

Breier, J. I., Gray. L. C., Klaas, P., Fletcher, J. M., & Foorman, B. (2002). Dissociation of sensitivity and response bias in children with attention deficit/hyperactivity disorder during central auditory masking. Neuropsychology, 16, 28–34.

Crandell, C. (1993). Speech recognition in noise by children with minimal degrees of sensorineural hearing loss. Ear and Hearing, 14, 210–216.

Crandell, C. C., & Smaldino, J. (Eds.) (2001). Classroom acoustics: Understanding barriers to learning. Volta Review,101(5).

Johnson, C. E. (2000). Children's phoneme identification in reverberation and noise. Journal of Speech, Language, and Hearing Research,43, 144–157.

Knecht, H., Nelson, P., Whitelaw, G., & 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.

Mayo, L., Florentine, M., & Buus, S. (1997) Age of second-language acquisition and perception of speech in noise. Journal of Speech, Language, and Hearing Research, 40, 686–693.

Nelson, P., (Ed.) (2000). Improving acoustics in American schools. Language, Speech, and Hearing Services in Schools, 31, 354–355.

Nelson, P. (2001) The changing needs of hard-of-hearing and deaf students in schools. Volta Review, 101(5), 23–31.

Nelson, P., Kohnert, K., Sabur, S., & Shaw, D. (2005). Classroom noise and children learning through a second language: Double jeopardy? Language, Speech, and Hearing Services in Schools, 36, 219–229.

Nelson, P., Sacks, J., & Hinckley, J. (2009). Auralizing adult-child differences. Paper presented at Acoustical Society of America.  

Niskar, A. S., Kieszak, S. M., Holmes, A. E., Esteban, E., Ruben, C., & Brody, D. J. (2001). Estimated prevalence of noise-induced hearing threshold shifts among children 6 to 19 years of age: The third national health and nutrition examination survey, 1988–1994. Pediatrics,108(1), 40–43.

Smith, E., Lemke, J., Taylor, M., Kirchner, H. L., & Hoffman, H. (1998). Frequency of voice problems among teachers and other occupations. Journal of Voice, 12, 480–488.

Soli, S. D., & Sullivan, J. A. (1997). Factors affecting children's speech communication in classrooms. Journal of the Acoustical Society of America,101, S3070.

Stelmachowicz, P. G., Hoover, B. M., Lewis, D. E., Kortekaas, R. W., & Pittman, A. L. (2000). The relation between stimulus context, speech audibility, and perception for normal-hearing and hearing-impaired children. Journal of Speech, Language, and Hearing Research, 43, 902–914.

U.S. Bureau of the Census (2000). Language use and English ability:2000 [PDF]. 

U.S. General Accounting Office, Health, Education, and Human Services Division (1995). Conditions of America's School (Document#: GAO/HEHS-95-61, Report # B-259307), February 1.

Werner, L. & Boike, K. (2001). Infants' sensitivity to broadband noise. Journal of the Acoustical Society of America,109(5), 2103–2111.


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