This is an appendix to testimony 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).
1(a). (back to appendix index)
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. (back to original document)Ideally, and eventually, all learning spaces should be included in a regulation. All new learning spaces, all additions to existing learning spaces, and all renovated learning spaces should be required to meet the new regulation. Virtually all spaces in schools are instructional spaces and that can include gymnasiums, lunchrooms, cafetoriums, swimming pools or other large assembly or recreational areas. Any space in which instruction or verbal communication is a function of the activities within the space should be covered.
Given the constraints of a fixed budget, however, the spaces selected for treatment should be prioritized and repairs or renovations phased accordingly. Highest priorities should be given to classrooms intended for verbal learning.
In addition to addressing the needs of students and faculty, schools in many cases also serve the needs of the needs of the local community for a variety of activities. It is not only the young student who should be accommodated in the educational facility but also any one else who will use the facility. They are entitled to access to the programs and services within the facility, per the ADA.
The recent GAO study found that 28% of existing schools in the U.S. identify *acoustics for noise control* as the dominant *unsatisfactory* or *very unsatisfactory* environmental condition. (Ref. 1) No follow-up survey was made to identify the magnitude of these noise problems or assess their impact. This is a previously unrecognized national need.
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. Results of these surveys should be announced periodically in the spirit of public accountability. The surveys at each school should be collated and passed up administrative channels to provide reports by school district, county, state, and nation. This will facilitate actions needed at local as well as national levels and will institutionalize attention to classroom acoustics.
The Educational building should be addressed as a class of building rather than singled out and a distinction made between user occupants. If the building is going to be designed to have a proper acoustic environment, it is far more cost effective to adopt a proper acoustic design at the beginning.
This will mean that there will have to be some hard decisions to establish priorities for that which is necessary as opposed to what is nice. That is where educating the public, or public officials come in.
1(b). (back to appendix index)
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? (back to original document)Acoustical guidelines or standards should be applicable to all learning spaces. Such guidelines exist in national standards of the nations of Portugal and Sweden. The Swedish Guidelines (Ref. 2) do not make such a distinction and while they might offer a good format to model. The sociological differences between Sweden and the U.S. as well as the basic reason, potentially unique to the U.S. that will drive the establishment of Acoustical Guidelines, the U.S. ADA laws and regulations. Society, as a whole, can benefit by addressing the special needs of those with hearing (or learning) disabilities in the school environment and thus, simultaneously, improving the acoustic environment for learning for students of all ages. Less stringent standards for non-classroom spaces are appropriate so long as exactly what constitutes a classroom is clearly defined.
What is not clear with respect to larger classroom or instructional spaces is whether the reverberation time (RT60) still needs to be, say, 0.4 - 0.6 seconds. The usual text book design charts that show recommended reverberation times as a function of volume indicate longer permissible reverb times as the volume of the room increases. Does this apply for hearing impaired people, or are their reverberation time needs fixed? This may deserve some discussion but at least it should at least be addressed in principle in a manner that gives the Access Board some indication of the direction they should move.
In considering the range of guidelines of standards for classroom acoustics, it is necessary to consider the variety of classroom sizes, configurations and teaching styles. This variety includes:
(a) Early childcare facilities
(b) Elementary Schools (Primary)
(c) High Schools (Secondary)
(d) Colleges & Post Secondary Schools
(e) Special Education Schools or Classrooms
Studies show that the youngest students have the most stringent acoustic environmental needs during critical stages of language and cognitive skills acquisition. This normally takes place in early child care and primary school settings. However, the need for good acoustics is great whenever new or unfamiliar material is presented orally. This can take place at any age, and so includes high school, college and post secondary education facilities as well.
Special education schools and classrooms have special acoustical requirements. Meeting these needs could simultaneously improve the acoustical learning environment for all students.
The reverberation time of larger classrooms is longer, even when the same type and percentage of surface absorption treatment is applied. Should longer reverberation time be permitted in verbal learning spaces? Should room size be limited? Should special seating accommodation be provided for vulnerable students? These are questions for further research.
Classroom configuration may be set by teaching style. This is not fixed, and can change even within a single class period. Desks and tables may be rearranged as the style changes from lecture to group instruction. Noise levels rise as students engage in-group discussion. The ideal placement of sound reflectors and absorbers changes with the teaching style. It would be useful for the teacher to have the flexibility to quickly modify the acoustical configuration accordingly.
2(b). (back to appendix index)
Are current design manuals, recommendations, and other technical assistance on acoustical design sufficient? (back to original document)No. While many reference books and design guides are available for acoustic design of spaces, they are seldom utilized for acoustic design of classrooms. These references include, but by no means are limited to the following.
1) *Architectural Acoustics*, David Egan, McGraw Hill, 1988
2) *AIA Architectural Graphic Standards, Eighth Addition*, John Ray Hoke, Jr. AIA (EIC), Chapter on Sound Control by Carl Rosenberg, AIA. (199?)
3) *Deaf Architects and Blind Acousticians, A guide to the Principles of Sound Design,* Robert Apfel, 1998.
4) *Acoustics and Noise Control Handbook for Architects and Builders*, Leland K. Irvine and Roy L. Richards. Kreiger Publishing Co., 1998.
5) *Acoustics: Architecture, Engineering the Environment* Charles M. Salter, Assoc., Inc. William Stout, Publisher, San Fransisco, CA, 1998
However, these reference books are not necessarily easily accessible and may not always reflect the needs of the population who need more acoustically-stringent accommodations or be easily used by the building design profession.
3(a). (back to appendix index)
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? (back to original document)Background. Only a limited body of research has addressed the specific acoustic requirements of children with disabilities that affect verbal communication and learning. We refer to these disabilities collectively as *verbal communication disabilities*. The research with children, as well as the research on adults with verbal communication disabilities, has identified three essential acoustic requirements for effective communication.
The first essential acoustic requirement is the sound pressure level of the verbal communication-all or most of the sounds must be audible for effective communication to occur. Sound pressure level (SPL) is often expressed in dB(A), a measure that weights the sound pressure levels at different frequencies based on the average loudness at each frequency.
The audibility requirement is especially important for children with hearing impairments that reduce auditory sensitivity to soft sounds with low SPLs.
The second essential acoustic requirement is the SPL of the verbal communication (signal) relative to the SPL of noise, where noise is defined as a competing background sound. The signal/noise ratio (S/N ratio), measured in dB, expresses the relative relationship between signal and noise levels. When both the signal and noise are measured in dB (either dB SPL or dB(A)), the S/N ratio is simply the subtractive difference between the two levels. For example, speech at a typical conversational level of 60 dB(A) in a background noise level of 50 dB(A) has a S/N ratio of +10 dB, while if the noise level were 65 dB(A), the S/N ratio would be -5 dB. Once verbal communication is audible, the S/N ratio-not the absolute levels of the signal and noise-determines whether effective communication can occur. When the level of the signal and the noise are increased by the same amount, as in systems that amplifies signal and noise equally, the S/N ratio does not improve. Small changes in S/N ratio have a large effect on verbal communication in listening situations with background noise. For example, a 1-dB change in S/N ratio can produce 10-15% change in the percent of words understood by adults in a simple verbal communications. Comparable results would be expected with children, although additional research is needed to document these effects.
The third essential acoustic requirement is reverberance. In enclosed spaces such as rooms, sound is reflected from the walls, ceiling, and floor. Reflected sound, or reverberation, reaches the ear of the listener slightly later than the sound arriving directly from the source.
Reverberation is commonly quantified as reverberation time (RT), the time required for the reflected sound to decay 60 dB below the level of the direct sound. Numerous studies of speech recognition by adults and children in reverberant environments have shown that the percent of words understood decreases as RTS become.
All three acoustic factors are known to affect children*s learning, specifically that of children with verbal communication difficulties. The relevant data are summarized below.
Specific acoustic requirements for children without verbal communication disorders
We note first that normal 6-year old children with no verbal communication or hearing disabilities require approximately the same SPLs as adults with no disabilities to recognize speech in a quite background.
However, children in this age group without disabilities exhibit recognition thresholds for sentences in background noise at S/N ratios averaging over 2-3 dB higher than adults (Gelnett et al, 1993; Stelmachowicz, 1998). In other words, a 6-year old without disabilities may require an S/N ratio 2-3 dB better than an adult to achieve to achieve the same level of verbal communication and verbal learning in situations with background noise. The average adult achieves effective verbal communication at S/N ratios better than -2.0 dB, while the average 6-year old children achieve effective verbal communication at S/N ratios 0 to +1 dB (Gelnett et al., 1993; Nilsson et al, 1994). The differences between children and adults decrease as the child grows older and vanish in the early teens. These age-related differences are usually attributed to the effects language development, which occurs throughout early childhood. This research indicates that the most stringent acoustic requirements for effective verbal communication and learning exist for the youngest children at the time they begin their schooling.
Specific acoustic requirements for children with verbal communication disabilities
A number of studies have shown that children with verbal communication disabilities have special acoustic requirements for effective verbal communication and verbal learning. Hearing impaired children require higher SPLs, better S/N ratios, and shorter RTS; while children with other disabilities may require better S/N ratios, and shorter RTS.
The terms *effective verbal communication and verbal learning* must be defined quantitatively before statements about specific acoustic requirements are made. For the purpose of this response, we define these terms as the ability to hear and recognize 95-100% of the words in short verbal communications. This definition is used because most of the research on acoustic requirements for children with verbal communication disabilities has employed recognition tests with simple words or short sentences.
Hearing impaired children. Hearing impaired children, regardless of whether their impairment is due to permanent sensorineural loss or to temporary conductive loss caused by ear infection (otitis media), require
1) higher SPLs,
2) better S/N ratios, and
3) shorter RTs for effective verbal communication and verbal learning than do children of the same age without hearing impairment. The child with sensorineural hearing impairment may utilize hearing aids or assistive devices that partially compensate for the child*s SPL requirements. Hearing aid amplification is usually set to compensate for approximately half the loss of sensitivity produced by the impairment. Thus, the SPL requirements for effective verbal requirements and verbal learning depend directly on the degree of sensorineural hearing impairment. For example, a child with a 50-dB loss of sensitivity may have hearing aids that provide 25 dB of amplification.
With hearing aids, this child may still require SPLs that are 25 dB higher than a child without hearing impairment. Temporary conductive impairments from otitis media can cause up to 30-dB loss of sensitivity, and are not usually corrected with hearing aids. A single SPL requirement for hearing impaired children can not be determined; however, individual requirements are estimated to range from 10-30 dB above the SPL requirements for children without hearing impairments, based on the typical range of severity of sensorineural and conductive hearing losses in children. Additional research is needed to further specify these requirements.
The S/N ratio requirements for hearing impaired children can be estimated from previous research (Finitzo-Heber and Tillman, 1978; Crandell, 1993).
This research suggests that children with as little as 20 dB hearing losses require S/N ratios 3-4 dB higher than for children without hearing impairment, and that children with 30 dB losses may require S/N ratios 5 dB higher. This research also shows that the use of hearing aids does not reduce the higher S/N requirements of these children. In fact, Finitzo-Heber and Tillman (1978) found that hearing-impaired children with hearing aids required higher S/N ratios than without hearing aids.
Thus, hearing-impaired children may require S/N ratios approximately 3-5 dB higher than normal hearing children of the same age to achieve effective verbal communication and verbal learning when background noise is present. Hawkins (1983) and Olson (1986) have both advocated classroom S/N ratios of +15 dB or higher for children with hearing impairments.
Research has also been conduced on the effects of reverberation on verbal communication and verbal learning in children with hearing impairment
(Finitzo-Heber and Tillman, 1978; Gengel, 1971; Hawkins, 1986; Nabalek and Pickett, 1974). Reverberation alone has detrimental effects on listeners* understanding of speech, even in a quiet environment. However, these studies have shown that the negative effects of combined poor S/N ratio and long RT affect children with hearing loss more than they affect children with normal hearing. RTs of 0.4 seconds have small effects on speech recognition in quiet and at high S/N ratios. However, in S/N ratios less than about +15 dB RTs greater than 0.4 seconds degraded speech recognition for hearing impaired children and for children without impairments. Even when the hearing loss is minimal (less than 20 dB) moderate levels of noise and reverberation may have a marked detrimental effect (Crandell, 1993; Nabelek, 1993). This research suggests that RTs in excess of 0.4 seconds may be unacceptable for verbal communication and verbal learning by all children, especially when they occur in the presence of background noise.
Children with limited English proficiency. Normally-hearing children with limited English proficiency (LEP), especially those children learning English as a second language (ESL) while in school, require better S/N ratios for effective verbal communication and verbal learning than children of the same age for whom English is their native language (Crandell and Smaldino, 1996; Soli and Sullivan, 1997). This research shows that S/N ratios must be 2-5 dB better for children with LEP than for children who are native speakers of English; although large individual differences exist among children with LEP, depending on when the child began learning English. Additional research is also needed to identify the source of the large individual differences among children with LEP.
No research has addressed the effects of reverberance on verbal communication and verbal learning in children with LEP and ESL children, although research with adults has shown that reverberance has a greater negative effect on speech recognition for ESL adults than for native English speaking adults (Bergman, 1980; Nabalek and Donahue, 1984).
Additional research is also required to establish specific RT requirements for children with LEP and ESL children.
Children with speech/language disabilities. Less research is available on children who have language disabilities in the absence of hearing loss.
However, some data show that language-impaired children show significantly higher speech recognition thresholds in noise than did their normal peers (Stollman et al, 1994).
3(b). (back to appendix index)
What are the relative contributions of low reverberation values and low background noise values to effective communication for people with hearing loss? (back to original document)Reverberation and background noise seem to contribute about equally to ease or difficulty of listening in adults (Nabelek, 1988, 1993). The combined effects of noise and reverberance may greater than the effect of either alone because poor S/N and long RT cause different types of speech errors. The effects of reverberation are minimized in quiet or high S/N ratios (+15 dB or better), but as RTs and noise levels are increased, their effects can be multiplicative, especially for listeners with hearing loss (Hawkins, 1986). Thus, both reverberation and background noise should be controlled to ensure that acoustical barriers are eliminated from classrooms. Short RTs reduce the negative effects of background noise and allow the advantages of binaural directional hearing to be used. However, all three of the acoustic requirements, adequate SPL, favorable S/N, and short RTS, must be met for hearing impaired children to learn effectively.
5. (back to appendix index)
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. (back to original document)Because the classroom of the future is an evolving concept, the full nature of these spaces cannot be predicted with certainty. It seems evident, however, from the huge investment in development that multimedia is intended to play a major role in the classroom of the future. It is important to recognize that the requirements for low noise and reverberation in classrooms are even more demanding in multimedia environments. The special acoustical needs of multimedia go beyond the setting of stringent limits on noise and ceiling reflections. The definition of multimedia has broadened from the 1960s idea of film, slides and audiotape media. The IEC TC100 Committee now defines multimedia to include integration of audio, video, graphics, data, and telephony. The term integration is meant to include the storage, processing transmission and reproduction of multimedia information.
Some insight may be obtained by considering the options of individual, small group, and large group learning facilities. Individual learning stations may consist of three sided booths, or carrels, in which students interact with modular multimedia systems to include audio, voice input/output, and video. Booths may have higher walls, higher attenuation, and more acoustical lining. Several of these stations may be present in a large room, attended by roving teachers who wander from station to station to provide individual assistance and monitor student progress as required. Here the noise sources include student*s voices and audio from adjacent carrels, equipment noise and HVAC noise. Booths (and to a lesser extent, carrels) reduce but do not eliminate acoustical crosstalk and noise from activities in adjacent learning stations.
Tall booth walls possessing high acoustical transmission loss, interior sound absorbing padding and sound absorbing ceilings will be advantageous. Sound isolation is improved by continuing both walls to ceiling height. Interior booth lighting can help by obviating the need for ceiling lighting fixtures that reflect sound into adjacent learning stations. Such booths may need individual HVAC registers or returns. The use of headphones in individual learning stations is customary and desirable, since their use can reduce interference from audio media that would otherwise be emitted from loudspeakers. Headphones can also permit the use of wide frequency range audio including low frequency sound, which would be more limited from small loudspeakers. The frequency response of such loudspeakers must be limited because low frequency sound can pass through the thin booth walls to adjacent workstations with little attenuation. However, it should be noted that some individuals are intolerant of wearing headphones for long periods. A small number of special rooms may be needed for long period usage with loudspeakers. With headphones, provisions may also be necessary to prevent hearing damage from excessive sound levels or long term listening at very high levels.
The noise levels of ancillary equipment, especially their low frequency content, must be strictly limited to prevent interference between adjacent learning stations. As an example, consider the modest noise of a small computer fan producing a noise level of, say 45 dB(A) at a students workstation. If the noise is mainly low frequency in content, it may pass through thin booth walls and over carrel tops with little attenuation. If there are 100 such fans from 100 workstations in the room, the combined noise level could conceivably approach 60-65 dB(A), depending on the room size and absorption. If so, the resulting din would be unsuitable for learning. Such strict limits may not be necessary if only a small number of workstations are used. To some extent, better booth isolation can be traded off with higher equipment noise.
Future multimedia equipment is expected to be energy efficient. If they are not, a large heat load can be anticipated a room containing many students and energy-consuming work stations. This may result in a noisy learning space. A large heat load requires special attention to HVAC design to ensure quiet. Unless HVAC ducts are adequately sized and lined, the air speed necessary for cooling may produce high noise levels. It is important to anticipate the maximum heat load so the HVAC system can be properly sized. This is best done prior to building construction and may be infeasible later.
The last two examples illustrate that a true systems approach to design is vital for multimedia rooms encompassing large numbers of individual learning stations.
Small group learning facilities may need to accommodate the use of loudspeakers for multimedia presentations. However, the interaction of students and teachers should not require amplification. Here too, the use of booths or carrels open on one side, and the adverse acoustical consequences of their imperfect isolation may be anticipated. Higher sound levels are necessary to communicate across the distance of a small work group then are required for an individual learning station. For that reason, similar, but more stringent demands may be placed on the isolation between group booths or carrels. If small groups need to teleconference with other classrooms, experience has shown that the requirements for low frequency noise may be exceptionally stringent.
The teacher may need to rove between small groups. This could, but need not present difficulties for maintaining an acceptable teacher voice level throughout each group room without electronic speech reinforcement.
If speech reinforcement is needed, special electronics could be needed to recognize a teachers presence at each group and limit speech reinforcement to that group.
Large group learning facilities (13+ students) will probably be used for multimedia presentations and lectures rather than group interaction.
Voice reinforcement should not be necessary except in the largest spaces.
These may be essentially lecture rooms and allow for only one talker at a time, usually the teacher. For lecture presentations in large multimedia rooms, student interaction from the *audience* may need to be facilitated by special microphone arrays that target an individual talker. If this is not provided, the ability of students to participate in large group learning will be diminished.
Large multimedia rooms may employ loudspeaker systems that are intrinsic to the multimedia equipment. Since the installed multimedia loudspeakers are already designed to cover the audience, it should be easy to integrate sound reinforcement, if necessary to permit lecture and student interaction. Other acoustical requirements are like those of other theaters for large groups, mainly low noise and reverberation. Especially large absorption and minimal reflecting surfaces may be needed in the back of the room. Speech levels should be at least 10 dB above noise levels.
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 (e.g. by the requirement for the use of headphones, etc.) Therefore, multimedia classrooms must be evaluated carefully for their compliance to standards for reverberation and background noise control. A separate set of guidelines for isolating equipment noise (e.g. by putting printers in a sound absorbing and isolating enclosure) is appropriate in considering the classroom environment of the future. This is one area where research is highly desirable.
6(b). (back to appendix index)
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? (back to original document)If the primary standard for classroom acoustics is to take the form of design criteria, with performance criteria invoked to validate that the design criteria have been properly implemented, then the following minimum design criteria must be established:
1) Reverberation Control. Reverberation control must be specified in design criteria as the number of square feet of acoustical absorbing material of a given NRC rating, mounted in a prescribed way, for a given size room. It will be useful to specify one or more nominal configurations, and adjustments from the nominal. For example, a nominal configuration is: 100% coverage of ceiling by hung acoustic ceiling of NRC of 0.75 for rooms of 9 foot height, with taller rooms adding xxx sq. ft. of absorbing material for each additional foot of room height. This treatment will produce reverberation times on the order of 0.6 seconds or less, depending on other furnishings, etc., in the room.
2) HVAC Systems. The very first criterion related to HVAC systems in new construction, is that no in-window ventilating systems be used. There are none produced today that can meet even moderated background noise levels while also meeting the necessary ventilation requirements. A checklist of appropriate HVAC practice should be appended to the standard to assure both appropriate choice of equipment, and its proper installation.
3) For new construction, an environmental acoustical survey is necessary so that construction choices and classroom siting assure that background levels in the classroom will meet the guidelines. The nominal configuration for classrooms is that there is no adjacency to spaces that generate significant noise, such as equipment rooms, gymnasium or other athletic facility, cafeteria, music rooms, et al. Further, the nominal configuration assumes that HVAC duct work is not shared with noise-producing facilities (without appropriate duct treatment through liners or mufflers) For such nominal spaces, one can define nominal acoustical standards for walls, floor-ceiling construction, windows, and doors, as found in the attached worksheet. When departing from the nominal design configuration for classroom siting, the specific impact of neighboring spaces must be assessed and appropriate action taken, including the retention of an acoustical consultant who can advise in the design stage and measure once construction is completed in order to assess whether performance guidelines have been achieved.
4) Other Background Noise Sources. If classroom siting, application of absorbing material for reverberation control, HVAC choices and implementation, and wall-ceiling, floor, window, and door choice and application fall within the prescriptions of the nominal design criteria, then additional background noise sources (e.g. highway or other environmental noise) must be anticipated and corresponding action must take place in the design phase in order to address the special noise circumstances. An acoustical consultant will be required in such instances.
In instances in which classrooms must be retrofitted to bring the classroom acoustic environment within the range of guidelines, then retrofit design should address each of the major points above, and, in consultation with appropriate acoustics experts, should implement changes that can be measured afterwards, to assure that design goals have been achieved. Each case is likely to be unique, so that no general prescriptions for remediation can be outlined without first assessing the nature of the problems through proper acoustic measurements.
7. (back to appendix index)
What is the square foot cost for new classroom construction today? 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? (back to original document)In typical classrooms for 30 students or less, the reverberation time governed by the sound absorption effectiveness of the ceiling material.
For a moderate sized classroom of 30* x 37* x 9* (approximately 10,000 cubic ft.) consisting of an untreated plaster ceiling, a hard surfaced vinyl tiled floor, and walls of painted masonry or drywall, the reverberation time of the empty room at 500 Hz is estimated at 2.22 seconds. This is unacceptably high.
The most common measure of sound absorption effectiveness for ceiling tile is the NRC (Noise Reduction Coefficient) By adding a suspended ceiling with a modest NRC rating of about 0.55, the reverberation time is reduced to 0.8 seconds. By adding a suspended ceiling with a better rating of 0.75, the reverberation time is reduced to 0.5 seconds, which is preferable.
The cost for a suspended acoustical ceiling with a modest NRC of 0.55 currently is around $.95 to $1.10 per square foot. For the better NRC of 0.75, the cost is around $1.30 to $1.45 per square foot. (Cost Data from Mr. Fred Folsom of Armstrong World Industries.) The sample room has a ceiling area of 1110 square feet.
In most classrooms, the dominant noise source, and the main obstacle to achieving low noise levels is the HVAC (Heating, Ventilating and Air Conditioning) system. In such cases, the cost of quiet HVAC is predicted to be the largest single cost element.
One organization whose members have much experience with HVAC noise is ASHRAE (American Society for Heating Refrigeration and Air Conditioning).
Current ASHRAE recommendations for the noise level in classrooms with normal hearing students is approximately equivalent to 45 dB(A) (neutral spectrum). For this situation, HVAC costs average roughly 10% of total classroom building costs.
The ASHRAE TC 2.6 Committee is responsible for the development and promulgation of HVAC system noise. Experience reported by individual members of this Committee is that the added cost of upgrading HVAC to achieve noise levels of 35 dB(A) would add about 4.5% to the total cost for building new classrooms.
Lower HVAC noise levels may unmask other noise sources that were previously unnoticed. The sound insulation from classrooms to adjacent spaces may also need attention. Better construction quality may be required to assure low noise transmission between classrooms. Higher sound insulation ratings for building facades may be needed to prevent outdoor noise sources from disrupting classrooms.
8. (back to appendix index)
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? (back to original document)The dollar benefits of good classroom acoustics are believed to be very large, but have not been documented and verified. The ASA strongly recommended that studies be made of the benefits of good classroom acoustics. If only the costs but not the benefits of good acoustics are documented, it should be no surprise that good acoustics is regularly excised from design budgets by dollar-strapped school boards.
One proposed, but unvalidated measure of dollar benefits of reduced noise is Acoustical Access to Education (AAE). The AAE index ranges from zero to 100%.The AAE considers a 40-dB range of noise levels actually found in classrooms from 30 dB(A) to 70 dB(A). Above 70 dB(A) verbal learning is assumed to be impossible, so AAE is zero. Below 30 dB(A) full acoustical access is provided, so that further noise reduction is unnecessary, and AAE is 100%. AAE assumes that every decibel of noise reduction in that range contributes equally. Each decibel of noise reduction raises AAE by 2.5%.
Following is an example of the use of AAE is in estimating the dollar value of reducing classroom HVAC noise from 45 dB(A) to 35 dB(A). The 10-dB noise reduction increases AAE by 25%. The dollar value is estimated from the cost for educating students in that space.
In 1993, the average annual cost for educating a student in a regular educational setting in the State of Colorado was $4064.75, which we round down to $4000. The value of a 10-dB(A) noise reduction is therefore estimated as 25% of that, or $1000 per student per year. With an average of 20 students in the classroom, the value of a 10 dB(A) quieter HVAC is $20,000 per classroom per year. If the HVAC system has a lifetime of 20 years, the value added is $400,000 per classroom. At $100/sq ft, the initial cost of an average-sized classroom of 1000 square feet is $100,000. The initial cost for the 10 dB(A) quieter HVAC was estimated at under 5% of total construction costs for that room, or less than $5,000.
The estimated savings of $400,000 exceeds the estimated costs of $5000 by a factor of 80, suggesting that good acoustics is indeed a good investment for America.
These estimates are thought to be conservative. The cost for educating students in special education settings is much higher than $4000/year.
One authority estimates an average cost of $14,000/year per special education student. Better classroom acoustics will allow some to be mainstreamed into ordinary, quiet classrooms. One study reports a 10% reduction in the number of students receiving special services after 3 years of improved acoustical access to education.
The benefit of good acoustics is especially great for the academically poorest students. With quieter classrooms, the number of failures (retention in grade) can be expected to decline. One study estimated the average cost to a school district per retention is $6000.
The dollar cost savings estimated above do not consider the dollar benefits to state and nation for good acoustics. These benefits accrue after the person has completed their education, and are additive to those estimated above. It is reasonable to assume that better education leads on the average to higher lifetime earnings. The ASA recommends that the economic benefits of good classroom acoustics to community and nation be estimated. The dollar benefits are unknown, but are believed to be quite large. Some indication of their size can be inferred from the following discussion.
Suppose that a person's lifetime earnings average $30,000 per year, and that, on average, good classroom acoustics increases these earnings by only 1%. Over a 40-year occupational lifetime, this increases national income by $12,000/person. If the classroom educates an average of 20 students/year for 20 years, the dollar benefit becomes $4.8M. The incremental cost for the benefit of quiet HVAC was estimated above to be $5000, considering only HVAC noise. Allowing a generous, equal amount for the other costs of good acoustics leads to a total estimated cost of $10,000 per quiet classroom. The huge cost-benefit ratio of 480 again suggests that good acoustics is indeed a good investment for America.