Optimizing acoustics in learning facilities

Rooms for focus

Figure 1: Noise reduction co-efficient (NRC) specification matrix for ceilings. Images courtesy Rockfon

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

Figure 2: Sound transmission class (STC) specification matrix.

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

Figure 3: Sound transmission class (STC) specification matrix.

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

The Den provides a multipurpose activity building with a gym and theatre to serve all of Noble Public School District’s (Ont.) students. TAP Architecture designed the two-storey, single structure and Optimized Acoustics for the facility’s wide range of activities. Forming the 17 clouds above the performing arts’ audience seating area, lay-in aluminum ceiling panels are finished to look like cherry wood. These metal ceiling panels with an acoustic backer can achieve up to 0.90 NRC to deliver the absorption required to make speech intelligible, and to make band music clear and comfortable to hear. Photo © Simon Hurst Photography

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.

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