Optimizing acoustics in learning facilities

by maz_atta | February 26, 2021 12:00 pm

Gary Madaras, PhD

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New, modern learning spaces are built to promote collaboration and inclusion by fostering a sense of togetherness and providing equal access to knowledge and resources. Specifying interior building products to achieve optimized acoustics is essential to support educational facilities’ design goals, and the teachers, staff, and students who depend on them.

Decades of research has proven loud noise can result in hearing loss, increased heart and respiratory rates, disruptions, and higher perceived stress levels. Noise does not need to be excessive to affect one’s well-being and learning capabilities. The acoustics inside classrooms determine whether students and their teachers can understand one another. This not only has an immediate impact on comprehension and retention, but also influences test scores, students’ morale, teachers’ job satisfaction, absenteeism, and short- and long-term health problems.

The benefits of a positive acoustic experience extend beyond traditional classrooms. Their relevance can be heard in gyms, aquatic centres, auditoriums, cafeterias, offices, theatres, band rehearsal rooms, recording and broadcast studios, fabrication shops, media centres, and more.

A Canadian national standard has been defined to address acoustics in schools, colleges, universities, libraries, and other centres of learning. The 2015 National Building Code of Canada (NBC)[2] incorporated acoustic requirements for residential dwellings, but not for educational, commercial, or institutional buildings.

At the provincial level, only Alberta has acoustic performance requirements in its 2020 Technical Design Requirements (TDR) for Alberta Infrastructure Facilities[3]. The importance placed on incorporating high-performance sound absorption into its learning facilities is summarized by the following statements:

Integrate surfaces with high acoustical absorption properties into the architectural design. This can reduce acoustical reverberation, decrease noise, and create comfortable environments with good speech communication.

Provide ceiling tiles with high sound absorption, acoustical roof deck, and sound-absorbing block wall. These surfaces are typically easy to refresh, are abuse-resistant, and cost-effective.

Open plan spaces (e.g. classrooms, offices) require ceilings with very high sound absorption; minimum standards may be too low for some situations.

Provide high quality flanking walls and ceiling baffles. This mitigates against future acoustic degradation if acoustic panels are replaced with conventional construction.

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Alberta’s TDR also provides more detailed acoustic performance requirements. In classrooms, the maximum permissible reverberation time (RT) is 0.60 seconds. The minimum noise reduction co-efficient (NRC) overhead is 0.55, which is very low, and would not achieve the maximum permissible RT. The lower NRC allows for designs where most of the sound absorption is instead being provided by the walls and floor. If the ceiling was the only sound-absorptive surface in the classroom, its NRC would need to be 0.75 or higher, depending on the ceiling height to achieve the required RT.

Beyond classrooms, Alberta’s TDR requires common areas to have ceilings with a minimum NRC of 0.70, providing good sound absorption in these active gathering spots. Music practice rooms are required to have even better sound-absorbing ceilings with a minimum NRC of 0.80.

Without acoustical guidance at the national or provincial levels (except for Alberta), some learning institutions have opted to develop their own acoustics standards. Since British Columbia does not offer a province-wide, uniform guideline addressing acoustic performance in educational facilities, the University of British Columbia (UBC) has developed its own language, which is a part of its Learning Space Design Guidelines[5].

The guidelines refers specification, design, and construction professionals to the Acoustical Design Standard for UBC Classrooms.[6] These acoustical standards emphasize:

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University classrooms are acoustically critical spaces in which verbal communication is crucial for teaching and learning. Non-optimal acoustical conditions in classrooms result in impaired verbal communication between teachers and students, impaired teaching and learning, and teacher voice problems. Students and instructors experience broken concentration, frustration, and fatigue. Students have difficulty hearing other students ask questions. The problems are particularly acute for hearing-impaired people, and those using a second language.

It continues, noting that “controlling and optimizing the acoustical conditions in a classroom, or other rooms for speech, involves three fundamental considerations: promoting high speech levels, controlling background noise, and optimizing reverberation.”

UBC assumes its existing “classrooms have ceiling absorption—often form all or part of a suspended acoustical ceiling—in order to control the classroom reverberation, in-class student-activity noise, and impact noise from spaces above the classroom.” RT requirements vary between 0.45 seconds for critical classrooms and 0.85 seconds for larger noncritical classrooms. More specific guidance on ceiling NRC ratings is not provided.

For most of Canada, acoustic requirements for the design and construction of learning facilities are non-existent. In May 2019, the Speech-language and Audiology Canada organization published a position paper on classroom acoustics that said, “Canada and its provinces and territories must adopt changes to their respective building codes to include standards for classroom acoustics. These standards[8] are essential to optimize learning, teaching, overall health, and quality of life.” The paper also referenced previous research indicating “children often work in classrooms with noise levels equal to or higher than the level of the educator’s voice, which leaves students listening to a ‘sea of noise.’”

Due to the absence of acoustics standards for learning spaces in Canada’s codes, designers, specifiers, and contractors are turning to a number of other options.

Start with functionality, volume, and shape

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When embarking on the acoustical design of a learning facility, first consider these basic questions at the earliest stages of each room’s design.

Function

What is the purpose of the space and what activities will take place in it? Rooms and spaces can be categorized into those for speech, focus, activity, or music.

Noise sensitivity

Who will be using the space and how important are speech intelligibility, privacy, and freedom from disruptive noise? Will the users’ sensitivity level be high, moderate, or low?

Noise potential

How much noise will be generated from inside the room and its adjacent spaces, such as from a lively meeting or noisy equipment? Will the noise level be high, moderate, or low?

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The core acoustic function of any room or space affects its natural shape and size. The finishes and their placement within the room also affect whether it is suited acoustically to its function. Glass, metal, stone, wood, and concrete are typically sound-reflective and can be used beneficially in a lecture hall to passively amplify the speaker’s voice. If they are used too liberally though, they result in excessive reverberance and can make speech difficult to understand. The most important factor, and the focus of this article, is the specification of the sound-absorbing finishes or treatments in relation to the function and size of the room.

 

Rooms for speech

Rooms for speech vary in size and function from a 10-seat meeting room and 100-seat lecture hall to a 1000-seat theatre. The primary acoustics goal in each is high speech intelligibility. Making speech intelligible inside rooms requires a loud sound source and low noise levels; in other words, a high signal-to-noise ratio. A well-designed speech room can hold listeners’ attention even as the speaker moves, turns away, or is blocked from direct line of sight and sound.

As a speech room increases in size, it becomes more difficult to maintain speech intelligibility and more critical to optimize the acoustics of the room. It is necessary to view the room as a passive amplification system. Larger speech rooms have lower signal-to-noise ratios because the average listener distance is greater and the speech signal has to travel farther. Therefore, speech rooms should be as small as practical for the intended capacity. The goal for the shape of the room is to minimize the average speaker-to-listener distance. The ceiling should be as low as possible to limit the volume of the room and decrease the amount of acoustic treatments needed to control reverberance. This is why a number of good speech rooms are fan-shaped with very low ceilings.

Rooms for focus

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Administrative offices, libraries, study lounges, and computer labs may be categorized as focus rooms with an acoustic goal of providing a space for relaxation, concentration, or private conversation. When these focus rooms are excessively loud and reverberant, they are stressful. Speech carries, and distracting noises may negatively affect accuracy, productivity, or decompression.

For focus rooms, speech needs to be attenuated, not amplified, and at times the background sound should be intentionally designed for both its content and greater loudness. Opposite to speech rooms, the goal in most focus rooms is a low signal-to-noise ratio. Focus rooms can be larger in floor area or height than they need to be for the intended capacity or function. They can also be shaped more so for esthetics than for particular sound reflection patterns. Note though that oversized focus rooms require more sound-absorptive treatments than smaller ones.

Rooms for activity

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A cafeteria, an aquatic centre, or weight-training gymnasiums are for neither speech nor music, but their acoustics are still important. The people in these potentially noisy rooms require overall acoustic control, while keeping the activity energized.

Other common spaces and areas, such as corridors, stairways, lobbies, and atriums, also belong in the activity rooms’ category because people are generally gathering in or circulating through these spaces without need to focus or listen carefully.

The acoustic goal for these activity rooms is to prevent excessive loudness and make announcements, especially during an emergency, understandable.

Activity rooms’ size and shape are very much determined by the functions within them. A pool or soccer field has specific size and shape requirements. The acoustic purpose does not drive them. Instead, the designer and specifier need to determine how much sound absorption is required based on the room size to prevent excessive loudness and make announcements or sports commentary over an audio system intelligible.

Rooms for music

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Rooms for music instruction, practice, rehearsal, and performance are the most critical and challenging from an acoustics perspective. The primary acoustics goal is to make the music clear, full, loud, enveloping, and enjoyable. Most of the music rooms in an educational facility are for individual or small group instruction, or for practice and ensemble rehearsals.

Unless the facility is a music college, there are usually only one or two main music performance spaces, and even those are typically multipurpose in nature. This adds a level of complexity to the acoustic design because the rooms need to be appropriate for different functions with varied acoustic goals.

Music room design is complex and challenging, and best determined by an acoustical engineer. These spaces are generally larger in volume relative to their occupancy than rooms for speech. The increased size is typically required for sound reverberation. As room volume increases, RT lengthens.

Only certain room configurations will develop a quality reverberant field. While low, squatty rooms may have the needed volume, the shape prevents a reverberant sound field from developing, and instead, it is plagued by echoes off the greatly spaced walls.

Acoustics consultants, such as members of the Canadian Acoustics Association, can assist in programming the music rooms during the conceptual design phase, and provide overall massing, shape, and size that will work appropriately as the design progresses.

Three steps for Optimized Acoustics

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Once an understanding of each room’s function, main acoustics goal, size, and shape are clear, the Optimized Acoustics design approach is used by design professionals to select the type and performance of the sound-absorbing materials, the sound-isolating capacities of the partitions and floor slabs, and design the background sound of each room and space.

Step 1: Select the appropriate NRC for the ceiling panels

How loud are the sounds inside the room and how sensitive are activities within the room to noise? For example, a classroom might have a moderate level of noise and a high sensitivity to noise, while a strength training room might have a high level of noise and a low sensitivity.

Use the ceiling NRC specification matrix in Figure 1 to determine whether good (NRC 0.70), better (NRC 0.80), or best (NRC 0.90) absorption performance is required for each room. When in doubt or when a uniform ceiling specification is desired throughout the building, select a higher NRC.

It is important to note reverberation is the most important, and often overlooked, source of noise that interferes with speech intelligibility. Unlike the temporary interruption when a truck or airplane passes, or when someone talks as they walk down the hallway, reverberation is always present and interferes with every spoken word all day long.

Step 2: Select the appropriate STC rating for floor/ceiling and wall assemblies

How loud are the sounds outside the room and how sensitive are activities within the room to noise? For example, is there a noisy lobby next door or gymnasium above?

Use the wall/slab sound transmission class (STC) specification matrix in Figure 2 (page 26) to determine whether good (STC 40), better (STC 45), or best (STC 50) isolation performance is required for each room. By definition, a wall with an STC rating is full height from floor slab to its underside or the roof above. Having walls that stop at suspended ceilings, leaving open plenum spaces above rooms, does not work acoustically and does not comply with acoustic standards or good design practices.

Remember, STC ratings higher than 50 should not be necessary if the building’s acoustic zoning and planning keeps noisy rooms from being adjacent to quiet rooms.

Step 3: Design the background sound level

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Quieter is not necessarily better, especially in focus rooms. Some background sound is necessary to mask annoying or distracting noise and to help achieve speech privacy, and to aid concentration or rest and comfort. This background sound can be from music, nature, mechanical systems, or electronic sound masking. Ensure the proper background sound, measured in A-weighted decibels (dBA), is achieved to deliver adequate sound privacy.

While designing focus rooms, use the table in Figure 3 to check the background noise level is in the right range relative to the STC rating of the walls and slabs selected in step two above.

Remember that for speech and music rooms, the background sound level should be as low as possible to aid in speech intelligibility, music clarity, and dynamic range.

Finalizing the acoustic design: speech

Optimal acoustics for speech rooms, such as classrooms, should include the correct amount of sound-absorptive surfaces anchored by a suspended, acoustic panel ceiling with a moderate to high NRC of 0.75 to 0.90. Larger rooms with higher ceilings or those with no other absorption will require ceilings on the higher side of that range, while smaller spaces with other absorptive surfaces might be able to meet the maximum RT requirements with a ceiling of only NRC 0.75. Absorption on the floors and walls can be avoided if the room is sized correctly and the ceiling is kept low enough. This saves cost initially and throughout the life of the facility, as the less durable acoustic materials are located overhead, out of harm’s way.

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Noise inside a speech room can come potentially from many different sources, including those located on the exterior of the building, in other interior spaces, or the building systems themselves. The building envelope should be designed to attenuate the level of environmental noise specific to the site. Interior partitions around speech rooms should always be full height, extending from floor slab to slab or the roof above. Stopping the partitions at ceiling level and leaving an open plenum above adjacent rooms is not recommended.

The building’s mechanical, electrical, and plumbing systems should operate quietly by locating noisy equipment remotely from speech rooms and by routing ducts and piping around, not over, speech rooms. The mechanical systems should meet maximum permissible noise levels regardless of whether the acoustic ceiling panels are installed or not. This provides design and functional flexibility in the future. This does not affect cost if the design team plans for this criterion as it lays out the floorplan and locations of the mechanical equipment.

Focus areas

As focus rooms can be oversized and creatively shaped per non-acoustic drivers, they often require a large extent of high-performing sound absorption overhead and on the walls and floor. Overhead sound absorption should have a minimum NRC of 0.90 and cover 75 to 100 per cent of the room. Walls should be absorptive as well with a minimum NRC of 0.70 for 50 per cent of the wall area or more. Ideally, the floor would be carpeted. This abundance of absorption keeps sounds from propagating through the space to aid in privacy.

In addition to implementing high-performing sound absorption, focus rooms may benefit from designed background sound to mask or cover up transient sounds that can disturb, distract, or annoy. Background sound provides speech privacy by making words hard to hear and understand outside close proximity. Selecting background sound depends on the room’s purpose and the desired acoustic experience. As examples: Music rejuvenates and energizes; nature sounds soothe and relax; electronic sound masking is benign, and is best at contributing to speech privacy.

The designed background sound level should be significantly louder than that which is permissible in speech and music rooms. Levels of 35 to 50 dBA or more are required compared to levels of just 20 to 25 dBA in large speech and music rooms. The approach is to create a low signal-to-noise ratio by increasing the noise level and by absorbing any reflections off the architecture so the signal is diminished.

Activity spaces

Sound-absorbing treatments in activity rooms often need to have impact-resistant surfaces and be up high, where they are less likely to get damaged. While more sound-absorbing materials are usually required for these rooms due to their large sizes, it is less in relation to their size compared to speech or focus rooms. Additionally, the performance level for the ceiling can be decreased to NRC 0.70 because less overall control is required. Ceiling panels with impact-resistant surfaces are likely to have lower NRC performance.

Activity rooms should not have too much sound absorption. These spaces often work better when there is a raised energy level supporting the activity. For example, an overly absorptive basketball gymnasium can make an audience of 500 people sound like an audience of just 50.

Background noise in activity rooms is typically less critical than in any others because speech intelligibility and music appreciation are not the primary acoustic goals. Generally, keep the background sound levels below 45 and 50 dBA.

Rooms for music

When a dedicated music performance space is sized and shaped correctly, very little, if any, permanent sound absorption is required. Rooms for music practice and rehearsal require more sound absorption than properly designed performance spaces. Multipurpose auditoriums for speech and music also typically require more sound absorption to meet their varied functions.

The audience and seating in performance spaces can provide adequate absorption in music rooms. If a lot of permanent sound absorption is required, either the space is oversized and one is trying to decrease the maximum RT, or the room is incorrectly shaped and one is trying to attenuate echoes. Both can be avoided with good acoustic design.

Rooms for music practice and rehearsal require more sound absorption at higher NRC ratings above 0.80 than do properly designed performance spaces. This is true especially in early education because young musicians have not yet mastered volume control. A marching band rehearsal room in a middle school requires most surfaces to be covered with NRC 0.90 or higher absorption to help control the power of the band. Another reason for having more sound absorption in music practice and rehearsal rooms is so the music student and teachers or directors can accurately hear subtleties of intonation and embrasure.

Figure 4  provides a summary of the primary acoustics design guidelines and performance metrics for speech, focus, activity, and music rooms in learning facilities.

Voluntary acoustical guidelines and standards

The Optimized Acoustics design process can be used during the design and specification of learning facilities in Canada when no provincial or institutional requirements are applicable. In some cases, though, acoustical requirements may be provided by an independent, third-party, voluntary standard, guideline, or rating system that the building owner or design team has opted to adopt.

The American National Standard Institute’s (ANSI) standard S12.60, Acoustical Performance Criteria, Design Requirements and Guidelines for Schools, frequently is cited in building codes, standards, guidelines, certification programs, and rating systems throughout North America.

ANSI S12.60 requires:

• sound-absorbing finishes, such as acoustic ceilings, so RT inside classrooms is no more than 0.60 for smaller rooms and 0.70 seconds for larger spaces;
• full-height walls between classrooms that have an STC 50 rating; and
• mechanical system background noise to be below a maximum permissible level of 35 dBA.

Adopting ANSI acoustic standards was among the recommendations made in the Speech-language and Audiology Canada’s position paper calling for building code changes to improve classroom acoustics. Similarly, the Canadian Hard of Hearing Association’s Universal Design & Barrier-Free Access said this “standard provides excellent guidelines for acoustical performance and it should be followed in both adapting of classrooms to accommodate hard of hearing students and in new designs generally. The standard was motivated by research[17] that shows that student performance generally is negatively influenced by noise and poor acoustics.”

Several voluntary, third-party building standards, guidelines, and certification programs championing sustainability and wellness also recognize people’s acoustic experiences contribute to their health and well-being. Many of these guidelines reference ANSI S12-60. Examples include:

1. The Canada Green Building Council’s (CaGBC’s) Leadership in Energy and Environmental design (LEED) v4 for Interior Design and Construction requires classroom acoustics to have:

 

• maximum RT of 0.60 to 0.70 seconds and use of a high NRC ceiling panel;
• full-height STC 50 walls; and
• maximum background sound levels of 40 dBA, although 35 dBA is preferred.

2. Green Globes for New Construction (ANSI/Green Building Initiative [GBI] 01-2019, Green Globes Assessment Protocol for Commercial Buildings), has been used by the Canadian federal government for more than a decade. It requires:

• classrooms to have a RT of 0.60 seconds or less, and ceilings with an NRC 0.80 or higher;
• classrooms to have full-height walls with an STC 50; and
• maximum background sound levels of 35 dBA (according to ANSI S12.60).

3. the International WELL Building Institute’s WELL Building Standard v2 examines 10 concepts and 108 features. Its sound concept “aims to bolster occupant health and well-being through the identification and mitigation of acoustical comfort parameters that shape occupant experiences in the built environment.” The Sound Concept includes:

• S02 “Maximum Noise Levels” optimization feature—requiring background noise levels in speech rooms to not exceed 35 dBA, in focus rooms 40 dBA, and in activity rooms 45 dBA;
• S03 “Sound Barriers” optimization feature—requiring activity rooms be surrounded by STC 60 partitions, speech rooms STC 55 partitions, and focus rooms STC 45 partitions;
• SO4 “Reverberation Time” optimization feature—requiring areas for learning to have a RT less than 0.60 seconds for spaces up to 929 m2 (10,000 sf), 0.50 to 0.80 seconds for spaces between 929 (10,000) and 1858 m2 (20,000 sf), or 0.60 and 1 second for spaces larger than 1858 m2 (20,000 sf); and
• S05 “Sound Reducing Surfaces” optimization feature—requiring areas for learning, open workspaces, conference areas, and dining spaces have 100 per cent of the room’s ceiling area be NRC 0.90 or higher. Partial credit (one point) may be given for ceilings covering at least 75 per cent of the room with panels having an NRC 0.75.

Beyond classrooms

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Learning facilities and spaces include far more than schools, colleges, and universities, and the teachers and students within them are equally deserving of a positive acoustic experience. The recently renovated and re-opened Stanley A. Milner Library in Edmonton was designed to meet, or exceed, Alberta’s TDR acoustic performance requirements.

As the downtown branch of the Edmonton Public Library (EPL), the new Milner Library reinvented its former box-shaped structure into a flowing, angular, modern icon, and reimagined its interior as a brighter, quieter, more inviting, innovative, public space. The $84.5-million expansion and rejuvenation encompasses six floors and 21,368 m² (230,000 sf). At its centre, a multi-storey atrium ascends within the building’s stacked floorplates, interspersed with exterior window views, and interconnected by light and openness.

Supporting the EPL’s and the library’s design goals, Teeple Architects selected four types of acoustic stone wool ceiling panels to contribute to the welcoming, comfortable, energy-efficient space, and to create a positive acoustic experience in a variety of different spaces.

The revitalized Milner Library’s design optimizes acoustics, categorizing each functional space or zone by its acoustic goals and utilizing an acoustic ceiling panel with the appropriate amount of sound absorption. Where high noise levels are expected or critical listening is required, the highest NRC of 0.90+ was specified. Where quiet concentration is needed or where a bit more excitement is desired, ceiling panels with NRC 0.80 are installed. In areas where less acoustic control is required, such as private rooms or circulation paths, lower performing panels of NRC 0.70 were used.

Finding a quiet space and avoiding noise was mentioned by 87 per cent of EPL’s customers in a 2012 survey[19]. Staff interviews confirmed a concern regarding the noise level in the library. Computer areas and places where teens congregated were called out as being noisy. Many said they valued designated quiet places to read, study, work, or write.

Responding to this feedback, the new Milner Library features enclosed collaborative spaces for group work, children’s programming, and more lively activities. Computer and workstations are distributed more widely throughout the building. Quiet zones are designated for reading and other tasks requiring concentration.

Helping manage noise and optimize acoustics to match each area’s function, the four types of acoustic stone wool ceiling panels provide the necessary range of sound absorption throughout the project with NRCs of 0.75 to 0.95.

The majority of Milner Library’s acoustic ceiling systems feature a mid-range NRC of 0.85 on five of the six floors. These include the staff’s offices and amenities room, the server room and computer labs, the conference and meeting spaces, the main floor’s Shelley Milner Children’s Library, and the second floor’s enclosed reading room.

The reading room has been called “an island of serenity” within the Milner Library and Edmonton’s downtown core. It is equipped with comfortable seating and work tables, a community gallery wall, and views on the east and north side onto Churchill Square. Here, in the reading room and in many of the library’s enclosed offices, sound-absorbing ceiling panels combine with full-height walls and moderate to high background sound levels optimizing acoustics to provide privacy and focused concentration.

Speech intelligibility and privacy are especially important in The Robert Tegler Trust Outreach Service at the Milner Library. Based on EPL’s community-led service model and the belief that great libraries welcome everyone, the outreach service staff works with EPL’s most vulnerable customers to help and empower them through literacy, education, connections, and social support.

More than 3200 black panels with an NRC of 0.85 were selected for the first and second floors. These deliver the best sound absorption for the high-tech, high-energy atmosphere of the 3-D printing area, the black box studio and adjacent studio spaces, and above laptop bars. The most acoustically critical areas in the third floor required the high NRC of 0.95 provided by an additional 881 m² (9488 sf) of black panels.

Ceiling panels with an NRC of 0.75 provide good sound absorption appropriately scaled for other areas’ functionality. These are installed on the first and second floors of library in its open common areas, above small group work areas, adjacent to the main circulation paths, and in other spaces where social conversations are expected.

In total, more than 6596 m² (71,000 sf) of acoustic stone wool ceiling panels were installed throughout the new Milner Library.

Conclusion

Regardless of available standards, design professionals can ensure optimal acoustics in learning facilities by using the right combination of highly absorptive ceiling panels, robust walls and floor slabs, and the right level of designed background sound level. Remember to follow the three-step approach for best results:

1. Acoustic ceilings are used to absorb noise and reverberation inside the room.
2. Full-height walls and floor slabs block outside noise from coming into the space from above, below, or next door.
3. Background sound is neither too quiet nor loud. Keep it low for speech and music rooms, and intentionally louder for focus and activity spaces.

[20]Gary Madaras, PhD, is an acoustics specialist at Rockfon. He helps designers and specifiers learn the Optimized Acoustics design approach and apply it correctly to their projects. He is a member of the Acoustical Society of America (ASA), the Canadian Acoustical Association (CAA), and the Institute of Noise Control Engineering (INCE). Madaras can be reached at gary.madaras@rockfon.com[21].

Source URL: https://www.constructioncanada.net/optimizing-acoustics-in-learning-facilities/

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