This testimony was written by the Acoustical Society of America (ASA) in response to a Request for Information about acoustics and educational facilities from the Architectural and Transportation Barriers Compliance Board (aka the Federal Access Board). You can also look at testimony by the Coalition for Classroom Acoustics.
July 27, 1998
To: Office of Technical and Information Services
Architectural and Transportation Barriers Compliance Board
1331 F Street NW
Washington, DC 20004-1111
Subject: Request for Information on Acoustics
36 CFR Chapter XI
[Docket No. 98-4]
Published in the Federal Register, June 1, 1998
The Acoustical Society of America wholeheartedly encourages the Access Board to develop and issue acoustical accessibility guidelines for classrooms and other learning facilities. The Societys response to the subject request is attached. In its response, the Society urges the Access Board to act expeditiously in the development and issuance of guidelines. Although additional research is recommended, sufficient knowledge about the impact of acoustical barriers on learning now exists to justify the issuance of guidelines.
Education is surely the forge of democracy. Since the time of Thomas Jefferson, Americans have recognized that an educated and informed electorate is the basis for participatory democracy. Today, as in our Nations past, education is the path through which new immigrants and native born citizens alike are assimilated into American life.
Education is also the engine of economic growth. In today's competitive world economy, an educated work force has become the condition for economic growth.
Acoustical accessibility guidelines and standards will improve access to education for millions of Americans. They will help young children learn to read and set them early on the path to achievement. They will help recent immigrants to assimilate more rapidly into American life. They will help to fulfill the dream of lifelong education for adults, and open the doors to higher education for all. They will help level the playing field for Americans with hearing, language and learning disabilities.
We believe that good classroom acoustics is not just common decency, not just common sense, not just a civil right, not just a duty to our children. We believe that good classroom acoustics is a good investment for America.
James E. West, President
Acoustical Society of America
July 29, 1998
To: Office of Technical and Information Services
Architectural and Transportation Barriers Compliance Board
1331 F Street NW.
Washington, DC 20004-1111
Subject: Request for Information on Acoustics
36 CFR Chapter XI
[Docket No. 98-4]
Published in the Federal Register, June 1, 1998
From: The Acoustical Society of America
500 Sunnyside Blvd.
Woodbury, NY 11797
Background on the Acoustical Society of America
As an advocate of good classroom acoustics, the Acoustical Society of America (ASA) is pleased to respond to this RFI. The ASA is a scientific organization founded in 1929 with a mission to increase and diffuse the knowledge of acoustics and to promote its practical applications. The ASA consists of over 7000 professionals in all fields of acoustics, including physics, engineering, architecture, experimental psychology, physiology, hearing science, speech science, and audiology.
The ASA has established formal Technical Committees and has charged them with fostering the various fields of acoustics. Many of the ASAs scientist and engineer members work in specialty fields that are closely related to the subjects of this RFI. These include its Technical Committees on Architectural Acoustics, Noise, Psychological and Physiological Acoustics, and Speech Communication. The ASA has created an interdisciplinary task force to study the problems of classroom acoustics. This task force has guided our response to the subject RFI.
The ASA's flagship publication, The Journal of the Acoustical Society of America, has published a number of studies that address the subjects of this RFI.
The ASA co-sponsored a special Workshop on Classroom Acoustics in December, 1997. The Workshop led to a coalition that reaches beyond ASA to include other individuals and organizations willing to act as advocates for good classroom acoustics.
ASA actively promotes the development of acoustical standards in the USA and throughout world. It holds the Secretariat for four national standards committees on behalf of the American National Standards Institute (ANSI). At its December 1997 meeting, the S12 Accredited Standards Committee on Noise established a Working Group to develop a standard or guideline for classroom acoustics.
The ASA wholeheartedly encourages the Access Board to develop and issue acoustical accessibility guidelines for classrooms and other learning facilities. The ASA urges the Access Board to act expeditiously in the development and issuance of these guidelines. Although additional research is recommended, sufficient knowledge about the impact of acoustical barriers on learning now exists to justify the issuance of guidelines.
Overview of the Acoustical Societys Response
Much of human learning involves verbal learning. Verbal learning embodies the symbols used for spoken, read, and written language. Early verbal learning includes understanding vocabulary and syntax, acquiring speech, and using language appropriately for social interactions. A particularly important part of verbal learning relates to early acquisition of reading and spelling. An impressive and growing body of research has shown that excellent acoustics in the home and classroom facilitates verbal learning. Conversely, poor acoustics in early childhood inhibits language acquisition and reading proficiency.
Increasingly, the pressures of rising enrollment, deteriorating buildings, poor acoustic design, and rising noise levels are making American schools less effective places to learn. However, the burden of noisy classrooms does not affect all children equally. The subject RFI has accurately identified the groups known to be highly vulnerable to poor acoustics. However, the burden of poor acoustics does not fall only on children. Teacher vocal fatigue is a common complaint in noisy classrooms. Vocal fatigue can result in significant lost work time and reduced teacher effectiveness.
Very poor classroom acoustics is obvious to anyone, but the problems caused by marginal classroom acoustics are insidious because they are not universally apparent. Students, teachers, and school administrators may not recognize the source of the learning difficulty. Vulnerable students in marginal classrooms may observe that others understand what was spoken while they do not. These students may develop an unduly low opinion of their cognitive abilities, leading to discouragement, boredom, discipline problems, and possible failure. Improving marginal classroom acoustics will help vulnerable students. Improving marginal classroom acoustics will also benefit teachers and other students by making the classroom a more effective and positive learning environment. Better classroom acoustics will help everyone and is a good investment for America.
The ASA believes that the RFI accurately and concisely summarizes the research findings on classroom acoustics. The RFI also poses a number of challenging questions. Additional research will be required to answer some of these questions. The ASA recommends that this research be pursued. The ASA also recommends that the Board move forward expeditiously with guidelines or regulations in parallel with this research. The ASA believes that the cost to America for delay will be very high. The US has undertaken the largest program of school building in its history. Without acoustical standards or guidelines, many new schools are likely to be built with acoustics that create barriers to learning. The cost of fixing poor acoustics by retrofitting classrooms is far higher than the cost of designing and building classrooms with appropriate acoustics. Acoustical standards or guidelines will help to ensure that new school construction will meet the acoustical requirements for effective verbal learning.
The following two sections present the ASAs response to the questions in the RFI. The first section provides concise answers to each question, while the second section is an Appendix with information that is more detailed with references for the responses to selected questions.
Prepared by the Acoustical Society of America
Should all rooms and spaces within a school setting be included in coverage? Some comment has identified gymnasiums, pools, and cafeterias as particularly problematic for students with hyperacusis, a heightened sensitivity to noise, and for those with learning and auditory processing disabilities. Such facilities are often highly reverberant due to their large areas of hard, sound-reflective surfaces. (additional notes)
All learning spaces should be included in a regulation, since virtually all spaces in schools are instructional spaces. ASA recommends that all new learning spaces and additions to existing learning spaces should be required to meet the new regulation at once. Existing learning spaces needing renovation should be phased in gradually.
The ASA also recommends that typical classrooms intended for approximately 30 or fewer students should be considered separately from larger classrooms, auditoria, and other learning spaces in new regulations and guidelines. Regulations and guidelines should be adopted for typical classrooms, and separate guidelines should be developed for other learning spaces. The recommendations for typical classrooms will also be appropriate for early childcare educational settings. If general standards are put forth for all learning spaces, compromises are likely to occur that would adversely impact verbal communication and learning in the typical classroom.
Learning spaces selected for renovation should be prioritized. Higher priority should be given to classrooms intended for verbal learning and to lower grades. For schools that also serve the needs of the local community, through ADA the community has some entitlement to access programs and services in school buildings. In these cases, community needs should also be considered.
Every school should be obliged to conduct an acoustical inventory of existing learning spaces so that those needing treatment or renovation can be identified and prioritized. This will facilitate actions needed at local as well as national levels and will institutionalize attention to classroom acoustics.
Should acoustic guidelines include coverage of these spaces? Would a less stringent standard be appropriate in non-classroom school facilities? What acoustical properties are appropriate in multi-purpose spaces that accommodate recreation, performance, and food service activities at different times during a school day? (additional notes)
Acoustical guidelines or standards should be developed for all learning spaces in which material is presented orally. Such standards already exist in other countries, including Germany, Great Britain, Italy, Portugal, and Sweden. There also is a precedent for applying less stringent standards to less-critical learning spaces in schools. The Swedish Acoustic Guide specifies requirements for seven types of schoolroom usage. [The reference for this guideline is the Appendix.] The most stringent requirements are placed on classrooms, group rooms, libraries, teachers rooms, staff rooms, and rest period rooms. Somewhat less stringent requirements are put on dining rooms and other spaces. This well-researched approach provides an excellent starting point for US acoustical guidelines or standards.
In view of the importance of early language acquisition, how should childcare settings be covered? Are there acoustical criteria in current health and safety standards for childcare facilities?
There currently are no known health and safety standards for noise levels in childcare and preschool settings. There are, however, considerable data regarding the importance of beneficial listening situations for young children. Studies show that the youngest students have the most stringent acoustic environmental needs during critical stages of language and cognitive skills acquisition. ASA recommends that standards/guidelines be developed for early childhood learning centers.
Should the Board consider the development of guidelines for a wider range of facility types for a universal range of users? If so, what facilities might be included?
The ASA recommends that the Board considers the development of acoustic guidelines for a wider range of facilities, and that this consideration be given its own RFI to allow input from a wider range of users. These facilities would include all public access facilities, such as restaurants, transportation centers, shopping malls, and public meeting rooms.
2. The Board has received information on several cases in which the acoustical environment was an issue in an individualized education plan prepared by a school system for a child with a hearing impairment.
Would a common standard for the acoustical design of educational facilities be helpful to design professionals seeking to provide acoustically satisfactory environments and to school systems seeking to comply with educational mandates for children with disabilities?
A well defined design standard for classroom acoustics would address those cases of hearing impairment in which active assistive listening devices are not required. Design manuals that currently exist in the US do not provide the practical aspects of implementation that are requisite for practitioners who are not trained in acoustics, e.g. architects and construction personnel. These practitioners should consult those trained in acoustics to assure that design details are not compromised. Practitioners should also have access, through a design standard or guideline, to practical protocols for the overall acoustical design of classroom spaces, and its integration with other classroom systems such as lighting and heating, ventilation, and air conditioning systems.
Are current design manuals, recommendations, and other technical assistance on acoustical design sufficient? (additional notes)
No. Existing reference books and design materials, some of which are listed in the Appendix, provide sufficient technical assistance on acoustical design. However, these materials are often unused for acoustic design of classrooms because they are unknown by or inaccessible to architects and construction personnel. These materials also may not reflect the more stringent acoustical design requirements for classrooms used by children with verbal communication disabilities. Thus, schools are often designed with little or no consideration given to acoustics. Too frequently, this happens because good classroom acoustics is seen as a cost without perceivable benefit.
A concise guideline document similar to the Swedish Guidelines would be an appropriate supplement to current design materials. Architects and designers will want a guideline that describes exactly what needs to be done in concise and simple terms and presented in a user-friendly form. An example checklist in this format for classroom acoustics is included in the Appendix.
Is there research that identifies the specific acoustic requirements necessary for effective listening by children with various hearing, speaking, and learning disabilities? What acoustical performance and testing standards are appropriate for classrooms in which children with auditory disabilities are integrated? Are there data that relate specific acoustical criteria to the usability of buildings and facilities by children with learning disabilities, developmental disabilities, and other disabilities that affect speech reception, learning, and communication? (additional notes)
A limited body of research has addressed the specific acoustic requirements of children with verbal communication disabilities. This research has identified three essential acoustic requirements for effective communication: the sound pressure level of speech, the speech/noise ratio, and the speech/reverberation ratio, as determined by the reverberation time of the classroom.
All sound pressure levels mentioned in this document are measured with frequency weighting A and are referred to as sound levels. Quantified values are identified, for convenience, by the symbol dB(A). Sound levels are a frequency-weighted measure of the absolute sound pressure level that approximates the audibility of sounds of different frequencies. Speech/noise ratios (S/N ratios) express the difference between the sound levels of the speech and noise. Since both the speech and noise are measured in dB(A), the S/N ratio, a relative measure, is simply the difference, in decibels, (abbreviated by dB) between the sound level of the signal and the sound level of the noise. Speech/reverberation ratios (S/R ratios) are defined in the same manner as S/N ratios, with the A-weighted sound level of the reverberant sound substituted for the A-weighted sound level of the noise. Reverberation times are defined as the time in seconds required for the reverberant sound to decay 60 dB. The symbol RT60 is used to designate reverberation time.
Normal elementary school children with no verbal communication or hearing disabilities require approximately the same speech sound levels as adults in quiet listening situations. However, these children require S/N ratios 2-3 dB higher than adults do to achieve the same level of communication in background noise. The most stringent acoustic requirements for effective verbal communication exist for the youngest school age children.
Children with verbal communication disabilities have special acoustic requirements. The hearing impaired child with hearing aids or the child with an ear infection (otitis media) may require 10-30 dB higher speech levels than the child without hearing impairment. Hearing-impaired children with mild-moderate impairments require S/N ratios 3-5 dB higher than unimpaired children do. The use of hearing aids does not reduce the higher S/N requirements of these children. Reverberation affects hearing-impaired children more than it affects unimpaired children. Reverberation times less than 0.4 seconds have small effects in quiet and at high S/N ratios, while longer reverberation times have a marked detrimental effect on hearing impaired children, especially when moderate background noise is present.
Children with limited English proficiency, especially children who are learning English as a second language (ESL), also require S/N ratios 2-5 dB higher than children who are proficient in English do. No research has addressed the effects of reverberation on verbal communication in this population, although reverberation has a greater negative effect on speech recognition for ESL adults than for native English-speaking adults. Less research is available on children with language disabilities in the absence of hearing loss. However, the limited data show that these children have significantly higher speech recognition thresholds in noise than their normal peers.
There currently are no acoustical performance and testing standards for classrooms in the US. The ASA strongly encourages the development of such standards. Nor are there standards for the measurement of S/N ratios and S/R ratios. The Societys ANSI S12 Accredited Standards Committee on Noise has formed a working group to develop a standard or guideline for classroom acoustics.
The research on acoustic factors that affect verbal communication and verbal learning in children with disabilities provides an empirical foundation for acoustic performance goals in classrooms. These goals are expressed in terms of the specific acoustic factors that affect verbal communicationthe level of speech or other signals, the S/N and S/R ratios, and the reverberation time of the classroom. The recommended goals take into consideration that some children in the classroom are likely to have more than one verbal communication disability.
The recommended goal for speech sound levels is 65 dB(A) throughout the classroom. Speech levels below the recommended level may create selective acoustic barriers for hearing impaired children in the classroom. In a typical classroom of 30 students with well-designed acoustics, talkers can usually produce the recommended speech levels without amplification.
The recommended goal for classroom S/N and S/R ratios is +15 dB throughout the classroom when the teachers or students voice is used as the signal. To achieve this goal, background noise levels should not exceed 35 dB(A) in unoccupied classrooms. S/N and S/R ratios that fall below the recommended goal may create selective acoustic barriers for hearing impaired children, learning disabled children, and children with limited English proficiency.
The recommended goal for classroom reverberation time is to achieve RT60 values of 0.4-0.6 second, or less, in occupied classrooms. When RT60 falls within this range, S/R ratios should meet the recommended goal throughout the classroom. Reverberation times longer than the recommended values may create selective acoustic barriers for hearing impaired children, learning disabled children, and children with limited English proficiency, especially in classrooms that do not meet the other acoustic goals. The occupants of the classroom will not provide a substantial portion of the total sound absorption needed to achieve the desired RT60 goal.
Since reverberation time increases in direct proportion to room dimensions, it will usually be impractical and costly to achieve the desired RT60 goal in large classrooms, auditoria, and learning spaces other than typical classrooms. The ASA recommends separate regulations for typical classrooms and for other learning spaces so that inappropriate compromises are not made for typical classrooms.
Classroom amplification technology has been used in some schools to address problems with classroom acoustics. This technology may be of limited use for these problems. Amplification technology should be used advisedly to achieve recommended speech levels and S/N ratios, and only in classroom lecture settings that meet the noise and reverberation goals. If this technology is used, amplified speech levels should not exceed comfortable listening levels throughout the classroom to avoid crosstalk between classrooms and to avoid problems for children with hyperacusis. Classroom amplification will have little or no effect on classroom reverberation time.
What are the relative contributions of low reverberation values and low background noise values to effective communication for people with hearing loss? (additional notes)
The combined effects of noise and reverberation are greater than the effect of either alone, because each factor causes different types of speech errors in adults. Both reverberation and background noise should be limited to ensure that acoustical barriers are eliminated from classrooms. Short reverberation times can reduce the negative effects of background noise and can allow the advantages of binaural directional hearing to be used. All three of the acoustic goals, adequate speech levels, favorable S/N ratios, and short reverberation times, must be met for the child with verbal communication disabilities to learn effectively.
Can the acoustical environment be improved sufficiently through design and construction measures for children with hearing and other impairments to receive significant communications benefit?
The ASA believes that with appropriate guidelines and standards for design and construction the acoustical environment in classrooms can achieve the recommended goals for speech levels, S/N ratios, and reverberation. Children with verbal communication disorders will receive significant communication benefit once these goals have been achieved.
At what thresholds of background sound and reverberation will children with various degrees of hearing loss be able to participate in meaningful classroom listening if aided by amplification technology?
Amplification technologies such as hearing aids may benefit the individual hearing impaired children who are using the devices by improving the audibility of sound in the classroom; however, hearing aids will also amplify background noise and reverberation. Hearing aids will be most beneficial when background noise and reverberation are limited. Some studies have shown that better S/N ratios and shorter reverberation times may be required when hearing aids are used. The recommended acoustical goals for hearing aid amplification technologies are the same as for hearing impaired children without hearing aids.
Technologies such as soundfield amplification systems may be beneficial in classroom lecture situations when the teachers voice must be amplified to reach a level of 65 dB(A) throughout the classroom. However, the classroom must satisfy the recommended goals for background noise and reverberation. Thus, the recommended acoustical goals for the use soundfield amplification technologies are the same as for hearing impaired children without hearing aids. Soundfield amplification is not recommended as a less costly substitute for acoustic design improvements when verbal communication and learning problems are encountered in noisy or reverberant classrooms.
Personal amplification (FM) systems transmit the teachers speech directly to the ear of the individual hearing-impaired child fitted with a FM receiver and earpiece. If the microphone for the FM system is held close to the talkers mouth, the S/N ratio at the earpiece can be improved up to 15 dB. These conditions are most likely to be met when the teacher is engaged in lecturing or direct instruction of the students. In other classroom conditions, such as group projects, music instruction, and peer-based learning, where individuals other than the person with the microphone must interact with the child, the FM earpiece may act as an earplug and attenuate speech levels.
The GAO report on school conditions highlighted the multimedia classroom as the educational facility of the future. The Board is interested in understanding the nature and characteristics of such a classroom, particularly the extent to which it may be interactive, with small group listening and discussion, multiple inputs from speakers and media devices, frequent changes in speaker-listener relationships, and other audio source conditions that may not be fully adaptable to amplification technologies. (additional notes)
The classroom of the future is an evolving concept, and multimedia is being readied to play a major role. The multimedia classroom is anticipated to have greater acoustical needs for quiet and low reverberation than non-multimedia spaces used for individual and group learning. The acoustical requirements for multimedia classrooms go beyond noise levels and reverberation times to include limits on equipment noise and thermal emissions. When teleconferencing is included, the noise and reverberation can be exceptionally demanding.
Multimedia technology makes noise, because of student interaction (tapping on keys), printer noise, and fan noise (especially for larger equipment such as servers). Audio output can be another significant source of noise unless controlled, for example, by the requirement for the use of headphones. Therefore, multimedia classrooms must be evaluated carefully for their compliance to standards for reverberation and background noise control.
The ways in which multimedia (film, slides, audio, video, graphics, data, and telephony) are integrated into classrooms will be specific to classroom size. Classrooms may contain a number of individual learning stations enclosed within carrels, or three-sided booths. Students may use headphones to reduce crosstalk between carrels, but computer-voice interactions will require good acoustic isolation between carrels. The substitution of masking noise for acoustical isolation may be unacceptable. If loudspeakers are used for multimedia audio or teacher/student intercoms, acoustical isolation requirements will be even greater. There are other special considerations when large numbers of individual learning stations occupy a single room. Systematic design will be necessary to prevent the accumulation of acoustical crosstalk and low frequency noise in these situations.
Acoustical isolation requirements for multimedia presentations in small group learning stations (4-12 students) are stringent because loudspeakers may be used to communicate audio. Small group learning stations may also employ three-sided booths or carrels to facilitate rapid entry and egress of a roving teacher.
Acoustical requirements for large group multimedia presentations (13+ students) may exceed those of traditional classrooms in the need for quiet and low reverberation. Requirements for the largest multimedia rooms may approach those of small theaters. For lecture presentations in large multimedia rooms, special audio resources may be needed to allow student interaction from the audience (e.g., directional microphones), especially in teleconferencing situations.
Soundfield amplification should not be necessary in settings with individual or small group learning stations. Its use in these settings will only exacerbate the problem of crosstalk. Loudspeakers will be needed for large group multimedia presentations, but amplification of the teachers voice should be unnecessary unless the room is very large.
Can good speech listening conditions be achieved by setting standards for reverberation time and background noise only?
Standards based on these acoustic performance criteria will be only partially beneficial because they fail to take into consideration the level of speech, the S/N ratio, and the speech-to-reverberation (S/R) ratio, which are critical for verbal communication and verbal learning. Standards based on these limited criteria may give adequate assurance of good listening conditions for small learning groups clustered around a teacher. However, as the class size enlarges, the level of speech, the S/N ratio, and the S/R ratio must be taken into consideration. In large or elongated rooms, for example, a teachers voice level may be inadequate to reach the back of the room without amplification, or be so affected by reverberation and noise as to be unintelligible.
Effective methods for achieving the recommended performance criteria depend on the size and dimensions of the classroom, as well as on the method of instruction. For lecture instruction in conventional classrooms, good listening conditions for speech are achieved with a non-absorbing surface in the ceiling directly over the teacher's position in the front of the classroom and absorptive finish at the perimeter. However, when teachers move around small groups of students in the classroom, auditorium acoustics design concepts are inappropriate. Instead, an acoustically treated hung ceiling over the entire room may be more effective. This treatment allows the direct sound and the side wall reflections from the teachers voice to achieve the recommended speech levels and S/N ratios if background noise levels are low enough.
Should other design variables, for example, room configuration or proportion, ceiling height, or size, be considered? The Swedish guidelines specify wall and ceiling construction types and values in addition to limiting background noise. Are these a useful model for possible guidelines? (additional notes)
Other design variables that are not considered in the Swedish Guideline need to be included in new guidelines if they are to be applicable to a wide range of learning spaces.
Guidelines related to reverberation times, especially those for large learning spaces, must allow for the fact that large rooms inherently have longer reverberation times. Design and construction costs make short reverberation times impractical in large rooms. However, short reverberation times may be unnecessary if high S/R ratios are maintained for listeners with verbal communication disabilities through preferential front seating and use of personal FM systems with headphones.
Room shape and absorber placement are important in large classrooms. In lecture type classrooms, sound reflecting surfaces should be behind, around, and directly over the teacher's position in the front of the classroom to project the teachers voice even when the teacher speaks while facing away from the students. In very large lecture classrooms, hard sound reflectors in mid ceiling are useful for projecting sound to the rear of the classroom. In group learning spaces of any size, reflecting surfaces are usually undesirable, and widespread acoustical absorption is preferred.
Background noise levels for classrooms are largely independent of room configuration, shape, and size. Thus, guidelines for background noise levels may not need to include other design variables specific to room configuration.
Guidelines should be specific to teaching style, which can change throughout the school day. In classrooms where different teaching styles are used, variable acoustic design features can be achieved through use of extensible surfaces with reversible absorbing and reflecting sides.
The Swedish guidelines are carefully researched and could serve as a starting point for US acoustical guidelines or standards. Their use of both airborne and impact sound insulation standards is appropriate in the US to limit crosstalk and impact noises between adjacent classrooms. Their rating methods can be adapted to US practice by employing the North American STC (Sound Transmission Class) and IIC (Impact Insulation Class) ratings instead of the European ratings.
A speech intelligibility standard would be a useful method to evaluate learning spaces. The Speech Transmission Index, which is mentioned elsewhere in this response, may be useful for this purpose. In questionable or difficult cases, including unusual designs, intense noise sources, unusual building siting, or severe acoustical requirements, the counsel of a qualified acoustical consultant should be sought early in the planning or design phase.
How might considerations of speech intelligibility, speech transmission indices, and other measures that rely on in-use testing be incorporated in acoustical design? What are the margins of error in acoustical equipment, testing, simulation, and construction?
Attainment of high speech intelligibility is the chief objective of classroom acoustic design, and objective measurement of intelligibility should be the yardstick against which success is measured. The Speech Transmission Index (STI) is an objective and standardized measure of speech intelligibility that can account for the effects of steady-state noise levels, reverberation, speech levels, and talker and listener positions in the classroom. The STI also provides a common measure for the design of new or renovated classrooms, as well as for the evaluation of finished spaces. STI requirements can be set to ensure classroom speech intelligibility levels. These requirements can be corrected for the developmental status of the children who will use the classroom, and for children with verbal communication disabilities. The ASA recommends further research to validate empirically the use of STI for setting classroom acoustic requirements; however, this research can proceed in parallel with the development of standards and guidelines.
The margins of error associated with acoustical equipment and testing procedures are on the order of 1-2 dB, especially if the procedures are performed by trained technicians. The error margins associated with computerized design simulations are difficult to estimate, since simulation tools are relatively new and evolving rapidly.
The margins of error that occur during construction are larger than the equipment, testing, and simulation errors. In many areas of building acoustics, there is a 3-6 dB difference between desirable and acceptable acoustic performance. There is also a potential difference of a similar magnitude between design expectation and results in the field. Good engineering practice aims for desirable conditions, recognizing that if these are met in the field, the results will still be acceptable. Practical implementation of design specifications requires a careful balance between the performance penalties (i.e., unacceptable acoustic barriers to learning) of failing to meet the specification, and the excessive construction costs associated with unrealistic specifications.
The outcome of this RFI may result in regulations at some level. It is important for regulators to understand this critical difference between desirable and acceptable design or performance goals for classroom acoustics.
What are effective means of acoustically retrofitting an existing classroom or other space that performs poorly for speech perception? How successful can such corrective action be in correcting perceived hearing and listening problems?
The first steps in acoustically retrofitting a classroom or other space are to determine the performance goals and the acoustical problems that need to be solved to achieve those goals. Trained acoustical professionals are essential in these determinations, and each case must be evaluated separately. There are many effective retrofitting solutions to acoustical problems in classrooms, e.g., addition of absorptive or reflective treatment to room surfaces to change room reverberation conditions, replacement of noisy equipment with quieter equipment, insulation of walls floors or ceilings, replacement of windows to prevent transmission of noise from other spaces, isolation of vibrating equipment to prevent structure-borne noise transmission, and sound enhancement. The degree of effectiveness of any retrofit is directly related to the effort put forth in solving the problem. Willingness to expend the time and money to correctly analyze, design, procure, construct and post-validate the retrofit will achieve the desired result. However, the acoustic retrofit of any space can be up to 10 times more expensive than the cost of initial design and construction that meets the same acoustic performance goals. Architects and construction personnel will need training in acoustics if they are to meet acoustic performance goals in new construction and in acoustic retrofitting of classrooms. A design checklist that may help to achieve these performance goals is included in the Appendix.
What is the square foot cost for new classroom construction today? (additional notes)
The following figures on square foot costs for new classroom construction are based on a survey by the Council for Educational Facilities International (CEFPI) of all school districts in the US in 1997. They are contained in the 1997 CEFPI School Construction Report available on the WEB at www.cefpi.com..
What additional square foot cost would be necessary to meet average industry recommendations for reverberation time (RT 0.6 - 0.8 seconds) and background noise (NC 35-40) for classrooms? What would be the added cost, per square foot, of achieving values within the ranges suggested by ASA (RT 0.4 - 0.6 seconds; NC 25-30)? What are the relative costs of meeting reverberation limits as opposed to background sound limits? What data are available on the costs of alterations to existing environments to improve acoustical conditions?
The additional costs per square foot needed to achieve the ASAs recommended acoustic performance goals reverberation are estimated as follows. Cost estimates are approximate and are intended only for illustrative purposes. In typical classrooms for 30 students or less, the reverberation time of the classroom (RT60) is governed by the sound absorption effectiveness of the ceiling material. If the room has an untreated plaster ceiling, a hard surfaced vinyl tiled floor, and walls of painted masonry or drywall, RT60 may be over 2 seconds. An RT60 of this magnitude would impose a formidable acoustic barrier to verbal learning. By adding a suspended ceiling with a NRC (Noise Reduction Coefficient) of 0.75 at a cost of $1.30-$1.45 per square foot to the typical classroom, the reverberation time can be reduced to 0.5 seconds, which meets the ASA performance goal for RT60. The cost per classroom would be approximately $1600an annual cost or about $80 per classroom and about $2.60 per student for classrooms with 30 students over the 20 year lifetime of the materials. The costs per student will be slightly higher in classrooms with fewer students. Even then, the cost of good acoustics is miniscule when compared with annual educational costs of about $4000-$6000 per student.
The cost of achieving the average industry recommendations for reverberation time and background noise is about 25% less than the costs of achieving the ASAs recommendations. Thus, the industry recommended values are achieved at annual savings of about $20 per classroom and about $0.60 per student. The dollar value of these savings pales in comparison with the educational consequences for children seated at a distance from the teacher, who will be unable to understand some verbal communication by the teacher and other children in the classroom.
In most classrooms the dominant background noise source, and the main obstacle to achieving the recommended background noise level is the heating, ventilating and air conditioning (HVAC) system. Individual experts, members of the American Society for Heating Refrigerating and Air Conditioning Engineers (ASHRAE), have estimated HVAC costs to be 10% of the total costs to build classrooms with approximately 45 dB(A) background noise levels. These experts also estimate that upgraded HVAC systems could achieve 35 dB(A) background noise levels for 14.5% of total costs. Thus, the incremental cost to achieve the ASA acoustic performance goal for HVAC background noise would is 4.5%, or $4.56 per square foot. This estimate is based on the median costs per square foot for new classroom construction in high schools, which typically have the highest construction costs per square foot. The median incremental cost per high school classroom is approximately $5000an annual cost of about $250 per classroom, or $8.40 per student in a 30-student classroom over the estimated 20-year lifetime of the materials. When the ceiling tile and HVAC costs are combined, the total annual cost per student of achieving the recommended acoustic goals is slightly over $11, a small price to pay for the removal of acoustic barriers in the classroom.
After HVAC background noise has been limited to the recommended levels, outside noise and noise from adjacent rooms may still contribute to unacceptable classroom noise levels in some schools. In these situations, the building facade and internal party walls may require retrofit improvements. For other schools, external noise sources, such as highway or rail traffic or aircraft overflights are the dominant sources of background noise. The added cost of reducing background noise levels from outside sources through better outdoor-to-indoor noise reduction can vary widely depending on the added noise reduction goals. However, such retrofit improvements have been carried out routinely in many school districts throughout the US, frequently with the benefit of financial support from the Federal government.
The Board also seeks information on the non-capital costs and savings associated with constructing and maintaining acoustically-appropriate classrooms and related educational facilities. What are the cost implications of such design and finishes decisions and operating procedures as room location and configuration, window operability, and carpeting? What savings might accrue from the elimination of some special education environments? (additional notes)
An informal method for estimating the cost of noisy classrooms and the savings associated with quieting classrooms has been proposed by the group Acoustical Access to Education. According to their method, 1 dB of noise reduction is estimated to produce a 2.5% benefit to verbal communication and learning in the classroom. Thus, the 4.5% one-time incremental cost to quiet a classroom HVAC by 10 dB from 45 dB(A) to 35 dB(A) is estimated to produce a 25% benefit. When the square-foot costs of classroom construction and the annual education costs per child are applied to these values, at least an 80-fold saving in education costs over the 20-year life of the HVAC system is projected. Moreover, this saving is obtained with an incremental investment in construction costs of only $5000 per classroom. These are conservative estimates and do not consider the costs of special education programs for children with verbal communication disabilities. Further savings are expected if some special education classrooms can be eliminated and the children from these classrooms can be educated in typical classrooms that satisfy the recommended acoustic performance goals. Although additional research on this issue is needed, the ASA believes that these estimates are strong evidence that good acoustics is indeed a good educational investment.
The savings associated with constructing and maintaining acoustically appropriate classrooms have not been formally and objectively documented. The ASA recommends further research to document the magnitude of the expected savings. The Board is encouraged to pursue the development of regulations and guidelines in parallel with this research.
How can compliance with acoustical design criteria be assessed prior to facility occupancy and use? How can time and physical variations in equipment manufacture, construction, and outside noise conditions be accommodated in a guideline? What testing and compliance practices have been used where standards are already in place?
Compliance with acoustical design criteria must begin with the initial design, continue through final design, equipment procurement, construction specifications, contractual requirements, construction, construction inspection, compliance field testing, and corrective acoustic measures if required. A design checklist requiring the sign-off of the architect, contractor(s) and an acoustical professional is essential. A draft checklist is included in the Appendix.
Acoustic field testing should be performed prior to occupancy by a qualified professional to determine compliance with design criteria. Tests should be conducted with all systems operating and with normal outside activity. Assessment may take the form of simple measurements of A- and C-weighted sound levels to validate that these values are within specified limits, and to verify that the difference between the C-and A-weighted sound levels does not exceed specified values. This latter performance criterion helps to control undesirable low-frequency masking noise.
Measurements of the Speech Transmission Index may also be used to verify compliance with the background noise and reverberation time requirements. Future research should identify typical classrooms in which acoustic design guidelines have been followed and in which the Speech Transmission Index has been measured. Designers, therefore, can be confident that these designs, properly implemented, will meet the Speech Transmission Index criteria.
The evaluation of present and potential outside environmental noise conditions should be included in the initial design of the facility, and the design should accommodate worst case scenarios. Transmission of exterior or interior noise into the tested space should be measured after construction is completed to ensure that the design criteria have been met. If the criteria are not met, the acoustical professional can prescribe corrective action measures to be taken before occupancy of the space.
Several methods can be implemented to accommodate the physical variations of equipment design and manufacture and still assure that the equipment meets the acoustical criteria of a design guideline. If acoustic performance standards are defined for the equipment, testing laboratories (either manufacturers or independent) can be used to establish compliance with these performance standards. Reference to these equipment performance standards should be included in any guideline.
Some states, e.g. California, do specify the noise reduction requirements for walls in multi-family dwellings and apartment houses. In addition, many local communities adjacent to airports have included external wall sound reduction requirements in their acoustic retrofitting of residences around airports.
Other means of predetermining compliance with a design specification include: scale model studies, full scale on-site trial mock-ups by potential contractors/suppliers, and development of building codes specifically designed for classroom construction. For example, local communities around airports often include external wall sound reduction requirements in their building codes. Requirements range from detailed design specifications to performance specifications on allowable interior noise levels or Noise Reduction (NR) through walls.
The ASA is not aware of any nationally based acoustic design requirements in such codes as the Universal Building Code. There are, however, state acoustic design requirements in California and, most likely in other states for apartment building construction. These building codes specify sound reduction requirements for party walls in multi-family dwellings or apartment houses.
10. Many teachers and administrators have had experience with open classrooms, in which several teaching groups may work concurrently in a single large space, and with enclosed classrooms of smaller size.
The Board is particularly interested in comments offering a comparison of the effects on students and teachers, in particular those with disabilities, of classroom acoustics in [open classrooms].
Some teachers advocate the use of soundfield amplification systems to address background noise problems associated with open classrooms. By amplifying the teachers voice, the S/N ratio will be improved in the teachers classroom. However, the amplified voice will also increase the background noise level in adjacent open classrooms. Thus, soundfield amplification may appear to solve the noise problems associated with open classrooms, but it does so by creating other noise problems in the adjacent classroom. Open classrooms should only be used if they meet the recommended acoustic performance standards.
Do noisy classrooms exacerbate teacher stress? Are there data available on the effects of classroom noise on teacher health, comfort, or performance?
Little published data are available on teacher stress and classroom noise. Although soundfield amplification systems should be used advisedly, there are informal reports that in noisy classrooms these systems help to reduce teacher fatigue and stress. In addition, the report of the MARRS project (Mainstream Amplification Resource Room Study) indicated that fewer teacher absences due to fatigue and laryngitis occurred when amplification systems were used.
Do schools and systems have information on student behavior and performance after acoustical improvements have been made?
No longitudinal studies have yet been reported in the research literature on the effects of acoustical treatments on student behavior and performance. Some inferences can be made, however, from cross-sectional studies. In one such study, grade-equivalent reading scores for third grade children from noisy classrooms were 0.4 years behind the scores for children from quiet classrooms. In this same study, sixth grade children from noisy classrooms were 0.6 years behind. There were no differences in grade-equivalent math scores between quiet and noisy schools for either grade. Similar results for reading scores have been obtained in other studies. Evidence of poorer reading scores from noisy classrooms is consistent with the view that the greatest effects of acoustical barriers are on verbal communication and verbal learning. More research, especially longitudinal studies, is needed to establish in more detail the relationship between classroom acoustics, verbal learning, and reading ability; however, the ASA recommends that regulations and guidelines on classroom acoustics should be developed concurrently with this research.
What approaches other than regulation under the ADA might be successful in achieving good acoustical design? What organizations and interests should be consulted in the Board's consideration of acoustical issues?
The ASA will do its part to facilitate the achievement of good acoustical design through its ongoing efforts to develop standards or guidelines for classroom acoustics. The ASA will also promote research and development efforts to achieve good acoustical design through the publication and dissemination of research in its journal and at its professional meetings. The ASA and other acoustical organizations can also run design competitions that focus on acoustical design problems that are unique to schools and classrooms.
The ASA recommends that the acoustical consulting and materials industries can play an important role in achieving good acoustical design for classrooms. These industries already have well established renovation methods for cafeterias and gymnasiums. This information, including good examples of design and renovation should be assembled into a database usable by architects and school designers.
Other programs by professional organizations should be directed toward educating the public and the design community on the importance of classroom acoustics. The American Institute of Architects should be encouraged to play a role in this process.
The Department of Education can also play an important role in addressing the problems associated with classroom acoustics. This Department already has the infrastructure for initiating research on acoustic design for educational facilities through its 5 Regional Education Research Labs and 27 University-based Education Research Centers throughout the US.
The ASA believes that exact nature of any product from the Access Board on classroom acoustics should be carefully considered. Whether a guideline, a design standard, or a legally-binding regulation is issued, the Board is encouraged to consider the forms of action that have been most effectively implemented and enforced for noise control purposes in existing city, county, or state building codes and regulations. The experience of states and municipalities with community noise control provides a close parallel to the regulatory issues that arise with classroom acoustics. The Board should also consider the recently developed regulations for acoustic design of Federal court facilities. Information should be gathered at the national level on the effectiveness of guidelines, standards, and regulations on noise control and other issues related to acoustics in parallel with promulgation of new standards or guidelines for classroom acoustics. In this fashion, the Board may be able to circumvent some of the problems encountered with previous codes and regulations related to acoustic performance.
Design guidelines, design standards, performance standards, performance testing standards and testing procedures are all-important tools for the achievement of good classroom acoustics. The key to their success, however, lies with the users of these tools: the school administrators, facility planners, architects, acoustical consultants, specification writers, procurement agents, cost analysts, contractors, equipment manufacturers and, most importantly of all, the clients. Teachers and parents are the clients and end users of good classroom acoustics who must be made aware of the importance of classroom acoustics to the education of their children and students. Well-informed educators and parents can insist that classrooms be designed correctly, that the correct equipment is purchased and installed correctly, and that the classrooms are tested to assure that they meet acoustical design requirements for effective learning.