Classroom Acoustics

Roles and Responsibilities

Audiologists, acoustical consultants, speech-language pathologists, classroom teachers, and administrators can and should work closely together in order to improve acoustic conditions in schools. Each profession plays a complementary role.

Audiologists

Roles and responsibilities of audiologists include:

  • understanding the principles behind sound acoustical design and the impact of classroom acoustics on educational outcomes;
  • educating others (including the general public, parents, children, and other professionals) regarding classroom acoustic concerns, the effects of acoustics on listening and learning, and the need for the application of good acoustical design in the planning and building process;
  • developing and disseminating information concerning classroom acoustics to the general public and policymakers;
  • acting as a resource for teachers, parents, speech-language pathologists, principals, and administrators;
  • surveying classroom acoustic conditions, including measuring background noise in dBA, measuring or estimating reverberation time, and measuring or estimating signal-to-noise ratio (SNR) and comparing these measurements to American National Standards Institute (ANSI) standards;
  • recommending technologies to improve the classroom SNR;
  • recommending the involvement of an acoustical consultant to evaluate and make specific recommendations for physical improvements to accomplish acceptable classroom acoustics;
  • establishing efficacy of improvements in classroom acoustics through various means, including comparing before and after physical measurements, behavioral measurements in the form of speech recognition scores, teacher or student report forms, and changes in student behavior (e.g., "on task behavior") or changes in achievement test scores as measures of efficacy;
  • documenting improvements and persistence of improvements over time;
  • providing habilitation and rehabilitation interventions as appropriate to minimize listening and learning barriers in the classroom, including listening training in the classroom, training in the use of clear speech, phonological awareness training, counseling for good listening (teacher, students, parents), visual communication training, communication repair strategy training, and auditory training;
  • monitoring the effectiveness of hearing aids or hearing assistive technologies, including working with other professionals to perform listening checks on equipment;
  • providing suggestions to families to improve the home listening environment as well as providing strategies to enhance a student's listening skills;
  • advocating for addressing classroom acoustic concerns and for the application of good acoustical design in the school planning and building process at local, state, and national levels;
  • educating members of the school team, including teachers and administrators, on their roles in advocating for improved classroom acoustics and implementing recommendations.

As indicated in the Code of Ethics (ASHA, 2010) audiologists who work in this capacity should be specifically educated and appropriately trained to do so.

Speech-Language Pathologists

The roles and responsibilities of speech-language pathologists (SLPs) working in schools include promoting efficient and effective education outcomes for students and supporting teachers in avoiding vocal abuse and overuse. In this capacity, SLPs work in conjunction with audiologists to provide information and recommendations for improving acoustics in classrooms and other learning spaces, including:

  • developing and implementing strategies to target excessive noise and reverberation in classrooms and other learning spaces;
  • advocating for addressing classroom acoustic concerns and for the application of good acoustical design in the school planning and building process at local, state, and national levels;
  • recommending the involvement of an audiologist or acoustical consultant to evaluate and make specific recommendations for physical improvements to accomplish acceptable classroom acoustics;
  • establishing efficacy of improvements in classroom acoustics, including comparing before and after behavioral measurements in the form of teacher or student report forms, changes in student behavior (e.g., "on task behavior") or changes in achievement test scores;
  • documenting improvements and the persistence of improvements over time;
  • providing habilitation and rehabilitation interventions, as appropriate, to minimize listening and learning barriers in the classroom, including listening training in the classroom and home, training in the use of clear speech, phonological awareness training, counseling for good listening (teacher, students, parents), visual communication training, communication repair strategy training, auditory-oral training, daily biological checks of hearing aids and hearing assistive technologies, monitoring classroom noise management, and using quiet areas of a classroom effectively;
  • educating members of the school team, including teachers and administrators, on their roles in advocating for improved classroom acoustics and implementing recommendations;
  • collaborating with the educational team to enhance the classroom listening environment and implement strategies in the classroom to enhance the listening skills of all students.

As indicated in the Code of Ethics (ASHA, 2010), SLPs who work in this capacity should be specifically educated and appropriately trained to do so.

Classroom Teachers and Administrators

For students with identified hearing loss and/or listening problems, accommodations and improvement strategies need to be implemented within the general education environment. Classroom teachers are instrumental in identifying students who may be experiencing hearing loss or other types of listening problems and in referring students to the appropriate professionals for further assessment. Building administrators can be instrumental in providing resources for collaborating to improve classroom acoustics and students' listening skills.

In classrooms where the acoustics are less than optimal, classroom teachers can accommodate students by using strategies that typically have been used for students with hearing loss, including

  • optimizing visual communication during instructional periods with high academic content,
  • gaining students' attention prior to delivering information,
  • using review strategies to identify key points,
  • encouraging students to practice active listening habits,
  • involving students in managing the noise level in the classroom.

Acoustical Consultants

Acoustical consultants have a variety of educational backgrounds, including engineering or physics. Consultants use knowledge of room acoustics, noise control, acoustical isolation, and audio systems to ensure the efficient distribution of desirable sound as well as the suppression of undesirable sound in and around classrooms and other structures.

Roles and responsibilities of acoustical consultants include

  • providing consulting services for new construction, including evaluating the design for interior room acoustics, interior and exterior acoustical isolation, mechanical system noise control, and performance sound reinforcement system design;
  • evaluating existing conditions in classrooms, including performing acoustical testing to determine the exact acoustic parameters of the room and comparing these to ANSI standards;
  • making recommendations for corrective measures to meet acceptable criteria to the extent possible.

Behavior of Sound In Rooms

In general, sound or noise radiates in waves in all directions from a point source until it encounters obstacles like walls or ceilings. Two characteristics of particular importance in architectural acoustics are

  • intensity—the loudness of the sound,
  • frequency—the pitch of the sound.

Both the intensity and the frequency of the sound wave will impact the sound/surface interaction. Some surfaces absorb sounds with high frequencies and reflect sounds with low frequencies. When sound waves strike a surface, one or several of the following can occur.

Transmission—sound passes through the surface into the space beyond it.

Absorption—the surface absorbs the sound.

Reflection—the sound strikes the surface and bounces off. Reflected sound can result in

  • discrete echoes, such as when the teacher's voice is continually bouncing off the back wall of a classroom,
  • flutter echoes, when a sound bounces rapidly between two flat, hard surfaces, such as two walls or a floor and ceiling;

Diffusion—the sound strikes the surface and is scattered in many directions (ASA, 2000).

Measuring Sound In Rooms

Decibels (dB): sound intensity levels can be measured in decibel (dB). In general, loud sounds have a greater dB value than soft sounds. A-, B-, & C-weightings refer to different sensitivity scales for noise measurement.

  • A-Weighting (dBA): follows the frequency sensitivity of the human ear at low levels.
  • B-Weighting (dBB): follows the frequency sensitivity of the human ear at moderate levels.
  • C-Weighting (dBC): follows the frequency sensitivity of the human ear at very high noise levels.

Many regulatory noise limits are specified in terms of dBA.

Reverberation Time (RT)—measures how quickly sound decays in a room. Reverberation times depend on the physical volume and surface materials of a room.

Noise Reduction Rating(NRR)—measures the effectiveness of materials to decrease sound exposure. NRR is expressed in dB. The NRR of a wall measures the percentage of sound produced in one room that passes through the wall into the neighboring room.

Signal-To-Noise (S/N) Ratio or SNR—the sound level of the signal of interest (e.g., teacher's voice) in dB in relation to the background noise level in the room. A positive SNR indicates that the signal of interest is louder than the background noise. In general, performance on intelligibility measures and comprehension tasks improves as the S/N ratio gets more positive. The SNR varies throughout the room as signal and noise levels vary.

Classroom acoustics can impact speech intelligibility, the percentage of words listeners correctly hear, and speech intelligibility in noise—the ability to recognize and understand speech in the presence of background noise. In the United States, it is common to use noise criterion (NC) curves to measure noise. NC curves have been established for rating indoor noise, noise from air-conditioning equipment, noise from technology used in the classroom, and other noise sources. The recommended NC level for typical classrooms is 25-30 with an equivalent sound level of 35-40 dBA.

Studies have shown that unfavorable listening conditions, including reverberation and noise, impact children even more than adults (Klatte, Hellbruck, Seidel, & Leistner, 2010; Shield & Dockrell, 2008). Both speech perception and listening comprehension in children were more impaired by background sounds than were speech perception and listening comprehension in adult listeners (Klatte, Lachmann, & Meis, 2010).

Classroom Acoustics Standards and Legislation

ANSI Standards

The American National Standards Institute (ANSI), which oversees the creation, promulgation, and use of thousands of standards and guidelines, and the Acoustical Society of America (ASA) have published the ANSI/ASA S12.60-2010 series of standards, including:

  • ANSI/ASA s12/60-2010/Part 1 American National Standard Acoustical Performance Criteria, Design Requirements and Guidelines for Schools, Part 1: Permanent Schools,
  • ANSI/ASA S12/60-2010/Part 2 American National Standard Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools, Part 2: Relocatable Classroom Factors.

These documents designate a standard methodology and targets for achieving adequate acoustic environments in schools and include acoustical performance criteria and noise isolation design requirements and guidelines. The standard's acoustical performance criteria and design requirements are meant to apply to the design and construction of all new classrooms or learning spaces of small-to-moderate size and, as far as is practical, to the design and reconstruction of renovated spaces.

Standards include guidance on

  • performance criteria for background noise levels,
  • performance criteria for reverberation times,
  • noise isolation design requirements,
  • use of classroom audio distributions systems,
  • conformance testing.

At the present time, the ANSI standard is voluntary unless referenced by a local or state code, ordinance, or regulation. However, school systems may require compliance with the standard as part of their construction documents for new schools.

Expert Opinion

  • The greatest 1-hour average A-weighted background sound level in a furnished but unoccupied classroom shall not exceed 35 dB; the C-weighted background sound level shall not exceed 55 dB (ANSI/ASA, 2010);
  • Unoccupied classroom reverberation time shall not exceed .6 seconds for average size classrooms or .7 seconds in larger rooms (ANSI/ASA, 2010; 2009);
  • For relocatable structures (e.g., temporary classrooms, trailers located outside the building), the standard provides a timed phase-in of the 35 dB requirement to allow for engineering changes that need to be implemented to achieve the goal. The RT requirement for average-size relocatable classrooms is a bit lower (.5 seconds), because these buildings generally have lower ceilings (ANSI/ASA, 2009).

Building Codes

Guidelines and requirements for classroom construction and applicable facilities are determined on the state and local levels. International and national model standards are developed by the International Code Council (ICC) and then adopted by states or localities. In some states, guidelines are uniform; however, many states use guidelines as a basic blueprint, with construction decisions made by each school sector or distribution. State requirements regarding standardized classroom size, materials, construction requirements, lighting, and similar factors are found in the information regarding capital construction and/or building requirements available from the state's department of education.

Currently, the International Code Council (ICC), which develops codes and standards used to construct homes and schools, does not reference the ANSI standards, and compliance with these standards is voluntary. Advocacy efforts to include ANSI standards in the IBC code in 2015 are ongoing. The U.S. Access Board maintains a listing of states that have adopted classroom acoustics standards and directives, and ASHA is actively advocating for the adoption of a new building code related to classroom acoustics. 

Americans with Disabilities Act

Currently, the Americans with Disabilities Act Accessibility Guidelines do not include provisions for the acoustical design or performance of spaces within buildings and facilities. The U.S. Access Board is undertaking rulemaking to supplement the guidelines by applying ANSI/ASA S12.60-2010 American National Standard Acoustical Performance Criteria, Design, Requirements, and Guidelines for Schools (Part 1 and 2). Once these guidelines have been adopted by the Department of Justice, they will become enforceable standards under the ADA (U.S. Access Board, n.d.).

Surveying Classroom Acoustic Conditions

Educational audiologists and/or acoustical consultants are responsible for assessing classroom acoustics and student performance within the classroom. The ANSI standard specifies acoustic measurement procedures that are used to determine background noise and reverberation, and audiologists and acoustical consultants are uniquely positioned to take these measurements in the classroom and compare them to the standard.

Acoustical assessments of classrooms and student performance within their learning environments typically include

  • formal noise and reverberation measurements, including
    • measuring background noise levels in dBA,
    • measuring or estimating RT,
    • measuring or estimating SNR;
  • behavioral performance measurements, such as speech recognition scores, teacher or student report forms, changes in student behavior (e.g., "on task" behavior) or changes in achievement scores;
  • comparison of current acoustical conditions and performance measurements with acceptable standards;
  • determination of the adequacy of the classroom for listening and learning.

Audiologists are responsible for formal noise measurements; SLPs may be involved in gathering behavioral performance measurements and teacher or student report forms and assessing changes in student behavior. Both professions can make recommendations on setting, such as moving desks, adding carpeting, changing window and wall coverings, and addressing appliance noises.

Acoustical consultants may be employed to evaluate existing conditions in classrooms and perform acoustical testing to determine the exact acoustic parameters of the room.

Modifications to Improve Existing Acoustic Conditions

After the results of classroom surveying are compared to ANSI standard reverberation time, background noise levels, and sound insulation criteria for wall, floor, and ceiling assemblies, a determination is made as to whether corrective action is needed. Recommendations are devised to meet acceptable criteria to the extent practical. Strategies for improving acoustical conditions include

  • modifying the physical characteristics of the room to provide better sound absorption,
  • properly fitting hearing aids and hearing assistive technologies for students with hearing loss or auditory processing difficulties,
  • purchasing sound-field systems for the room when reverberation is acceptable,
  • implementing habilitation and rehabilitation interventions (listening training, phonological awareness training, training in the use of clear speech, visual communication training, auditory verbal training, monitoring classroom noise management, etc.).

The classroom teacher, school principal, custodian, and the district's facilities department may be engaged in the efforts to improve acoustics. Modifications should be based on an evaluation of the classroom acoustics and specific circumstances for students. Measurements taken before recommendations are implemented should be repeated after changes have been made to determine the efficacy of the changes and improvements and document improvement persistence over time.

Internal Modifications

Modifications can be made to the physical characteristics of the room to reduce the reverberation and reflection of sound. Typically, noise is controlled at the source or along the path. To decrease reverberation of a sound either the volume of the room must be decreased or the sound absorption must be increased. Reflection can be controlled using absorption and/or diffusion.

It is important to consider the sound absorption coefficient for various absorptive materials for ceilings, walls, and floors, including the critical frequencies (i.e., speech frequencies) where materials provide the greatest and least absorption. Most room surface materials do not absorb low-frequency sounds as effectively as high-frequency sounds. Specific modifications are listed below.

Ceilings

In general, a ceiling height of 9-12 feet is optimal for the classroom listening environment. If a classroom has ceilings higher than 11 feet, acoustical panels may be needed on both ceilings and walls. Any acoustical ceiling tile used should have a sound absorption coefficient rating sufficient to achieve the desired noise and/or reverberation reduction. Strategies for mitigating noise include

  • adding a suspended ceiling of sound-absorbing tile to decrease room volume and increase absorption;
  • replacing existing ceiling tiles with high-NRC-rated (0.75 or better) acoustical tiles;
  • suspending banners, flags, student work, and plants from the ceiling to contribute to the reduction of noise and reverberation.
Floors

Strategies for mitigating noise include installing carpet over a pad to absorb high-frequency consonant sounds and dampen noise from students and from movement of classroom furniture. The thickness of the carpet pad contributes to the overall decrease in amount of internal noise in the classroom. In a classroom setting, carpeting may generate concerns regarding indoor air quality and the potential for allergic reactions.

Furniture

Strategies for mitigating noise using classroom furniture include

  • staggering desks and tables so sound will not travel directly to hard reflective surfaces, such as walls, chalkboards, and windows;
  • using felt or rubber caps on chair and table legs to help reduce noise in classrooms, particularly if floors are not carpeted;
  • arranging classroom furniture so that instruction occurs away from noise sources (e.g., HVAC systems, aquariums) and to accommodate the teacher's instructional style to reduce noise and the distance between the teacher and the students;
  • placing mobile bulletin boards and bookcases at angles to the walls to decrease reverberation;
  • covering the table surface with fabric in areas where younger children are handling manipulatives or playing with toys;
  • lining study carrels with acoustic tiles and installing rubber pads underneath equipment (e.g., computer, typewriter) to reduce noise in these areas.
Lighting

Some fluorescent lighting systems emit a constant noise. Regular maintenance should be employed, as ballasts can become noisy and create a 60 dB 1000 Hz (or thereabouts) hum. Where possible, house the lighting system above the acoustical tile ceiling to lessen the amount of noise generated.

Mechanical Equipment Noise

Mechanical system noise accounts for the highest percentage of noise complaints in the United States. High ambient noise from mechanical equipment—such as noisy heating, ventilation, and air conditioning (HVAC) systems—can be mitigated by

  • locating main classroom instructional areas away from external HVAC systems,
  • adding a custom built sound enclosure around unit ventilators,
  • adding sound-lined ductwork to the unit(s) to attenuate air distribution noise,
  • replacing window units with a quieter split system or through-wall model.

Other modifications for noisy ducted systems include

  • increasing the open area of grilles and diffusers,
  • rebalancing the system to reduce air volume,
  • relocating ductwork and diffusers away from key teaching locations,
  • adding separate duct runs to eliminate noise from common use,
  • adding duct length to attenuate noise,
  • adding sound lining to ducts.

Equipment such as computers, projection units, and aquarium pumps add to mechanical equipment noise.

Walls

Strategies for mitigating noise through modifications to existing walls include

  • adding soft materials, such as fabric-faced glass fiber wall panels, carpet, or acoustical ceiling tiles;
  • adding sound-absorbing panels high on walls at sides and rear of room;
  • placing an absorptive or diffusing material on the rear wall of a classroom to prevent the teacher's voice from reflecting from back to front;
  • covering fabric-faced glass fiber panels on parallel walls to reduce echo—which strategy works particularly well if panels are staggered along opposite walls;
  • adding acoustical panels or cork, felt, or flannel bulletin boards;
  • upgrading partitions between classrooms and adjacent areas (often used in open classroom designs) to achieve Sound Transmission Class (STC) ratings as recommended by ANSI standards.
Windows and Doors

Strategies for mitigating noise through modifications to windows and doors include

  • adding draperies, acoustically treated blinds, or shades to windows to absorb sounds;
  • installing double-pane windows to offer more protection from outside noise;
  • adding good quality drop seals and gaskets, replacing doors with tight-fitting solid core doors with seals and gaskets, or installing special sound-control doors;
  • adding storm windows, replacing existing windows with thermal insulating units, or installing specially fabricated sound-reducing windows.

Exterior Noise

Exterior noise also contributes to the background sound in a classroom. Modifications to reduce exterior noise include

  • using exterior barriers and landscaping to deflect or absorb unwanted sounds,
  • ensuring building walls are free of cracks, receive regular maintenance, and have a high sound transmission loss (STL) level.

New Construction

Good acoustical design begins at the outset of the building planning, design, and construction process. It is easier to incorporate appropriate acoustical materials at the beginning of the process, rather than retrofit materials after the fact.

The architectural team responsible for the design of a new school building often employs acoustical consultants to evaluate the design for the interior room acoustics, interior and exterior acoustical isolation, mechanical system noise control, and performance sound reinforcement system design. As a rule, acoustical consultants are not asked to design sound reinforcement systems (i.e., sound-field amplification systems) for classrooms.

Acoustical consultants provide consulting on:

Interior Room Acoustics—selecting acceptable wall, ceiling, and floor materials or finishes for the classroom so that the reverberation time of the room meets or exceeds the reverberation design goal specified in the ANSI standard.

Background Sound Levels—performing various types of design calculations, supported, whenever necessary, with noise measurements, to determine if the ANSI-specified background noise level design goal of 35 dBA could be met.

Mechanical Noise—calculating sound levels in a classroom using the design documents provided by the mechanical engineers, and, if the 35 dBA design criterion is exceeded, recommending sound attenuation devices to meet the design goals.

Exterior Noise—measuring the sound levels at the potential site of a new school, particularly if the building is in a high noise level area, such as close to an airport or major highway; making recommendations for noise isolation or performance of exterior windows and wall sections to ensure that the requirement regarding the maximum background sound level is met inside the room; making recommendations on sound insulation design of the external walls and roof assembly.

Partition Design—ensuring partitions between the classroom and adjacent areas are designed or upgraded to achieve Sound Transmission Class (STC) ratings as recommended by the ANSI standard of 50 STC between classrooms, 45 STC between classrooms and corridors, and 60 STC between classrooms and high noise level rooms like mechanical rooms or music rehearsal rooms. To achieve these ratings, walls must be sealed to the underside of the structure above. Walls that stop just past acoustical tile ceilings will not achieve these ratings.

Information on the interior finishes, partitions and window details, and mechanical system modifications should be given to the design team so that these features can be incorporated into the final design documents for the building.

Classroom Audio Distribution Systems (CADS)/Sound-field Amplification

Classroom audio distribution systems (CADS), sometimes referred to as sound-field amplification systems, used in conjunction with the noise and reverberation levels specified in ANSI S.12.60 may be of benefit in classrooms under certain conditions (Smaldino & Crandell, 2000).

In cases of moderate activity noise, the CAD/sound-field amplification system can be employed to augment the teacher's voice—especially when she/he is a quiet talker—and as multimedia sound distribution systems. An amplification system should not be used as a substitute for good acoustics. To ensure successful use of sound-field amplification systems, the ASA advises that classroom noise levels and reverberation times be documented prior to installation. Acoustical consultants or credentialed school audiologists (properly trained and equipped) may screen and document classrooms for CAD/sound-field system installation.

ASA Panel on Public Policy, 2013

When a CADS is considered, evaluated, and installed, it is important to carefully evaluate classroom acoustics (especially reverberation time) and to follow a systematic process to determine the most appropriate solution for a given classroom. Classroom acoustics are a significant factor influencing the efficacy of CAD/sound-field systems (Dockrell & Shield, 2012). Installation of these systems in classrooms is done in collaboration with an educational audiologist, with consideration given to

  • emphasizing sound distribution rather than amplification,
  • understanding that CADS cannot substitute for poor acoustics,
  • providing training in the use of CADS to classroom teachers,
  • conducting validation procedures to document that the system is providing an appropriate speech-to-noise ratio, typically +10 to +15dB SPL, depending on classroom ambient noise, and that speech is evenly distributed throughout the classroom (American Academy of Audiology, 2011).

Options to consider when selecting CADS include

  • transmitter options (e.g., FM radio, infrared light, etc.),
  • digital modulation,
  • receiver options,
  • loudspeaker options,
  • listening requirements for specific populations (e.g., students with hearing aids, cochlear implants, bone-anchored hearing aids, personal FM).

Considerations during set-up of the system include the placement of loudspeakers, intensity levels, frequency response, and feedback. Systems should be adjustable so that their sound output does not intrude into adjacent learning areas.

Expert Opinion:

  • Classroom audio distribution systems, if installed, shall have uniform coverage within ±2.5 dB for octave-band sound pressure levels with midband frequencies of 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz (ANSI/ASA, 2010).

Advocacy

Audiologists and speech language pathologists are in an excellent position to advocate for good classroom acoustics so that the concept of creating good classroom acoustics is valued and accurate listening is accessible for all students. Steps in becoming an effective advocate include

  • becoming as knowledgeable as possible on the subject of classroom acoustics;
  • surveying unoccupied classrooms to document the problem using a sound level meter that can measure down to 35 dBA;
  • assessing how many students and staff with disabilities could benefit from improved acoustics in a specific school and/or district;
  • forming advocacy groups of key stakeholders, including PTA, school board, teachers unions, and special education professionals;
  • presenting the need and rationale for good classroom acoustics repeatedly to those who are in positions to effect change.
  • engaging with local, state, and national professional organizations, including disability advocacy groups such the Alexander Graham Bell Association for the Deaf and Hard of Hearing (or its local chapters), Hearing Loss Association of America, and Acoustical Society of America (or its regional chapters).

See advocating for change for more information.

Content Disclaimer: The Practice Portal, ASHA policy documents, and guidelines contain information for use in all settings; however, members must consider all applicable local, state and federal requirements when applying the information in their specific work setting.