Reducing Noise in Learning Spaces
Beyond the basics of a mere shelter, architects and engineers regard buildings as places that facilitate and celebrate human interaction. Learning, like any other form or human interaction, is necessarily a sensory exchange – there is simply no other path to the brain than through the senses. Every new building provides an opportunity to craft the sensory balance between signal and noise, stimulation and calm.
Because the auditory sense is so critical for learning, and because hearing loss in young children can affect their learning, any new building designed for education should be as quiet as possible. The exterior shell should be shaped to deflect and absorb traffic and other outside noises, ventilation systems should be designed to prevent machine noise from traveling through ducts and floor plans should be zoned to keep noisy spaces away from quiet spaces. The strategies are exhaustive and achievable.
So what can be done to reduce noise in existing learning environments?
To be cost-effective, acoustical retrofitting needs to be approached no less methodically than the noise strategies for a new building. As in the scientific method, the first step is to thoroughly define the problem – identify all sources of noise in each space to be treated and rank them according to sound pressure level and frequency. While highest priority is generally given to sources in the middle to upper portions of the human speech frequency range (500 Hz to 6,000 Hz), it may be advantageous to address noises above or below that range if they are interfering with attention. For instance, a faulty belt in a mechanical unit cycling rapidly between 8,000 and 10,000 Hz, even at relatively low volume, is likely to distract or annoy any student forced to sit nearby.
As each source of noise is identified, it should be classified into two types – those which originate outside and filter in, and those generated within the space being treated.
Noise From Outside
Outside noise can infiltrate through weak links that occur within the wall, ceiling and floor assemblies, or at the places where they adjoin one another. Often referred to as “flanking paths,” these weak spots occur commonly in walls above suspended acoustical ceilings. Wherever a pipe, duct or conduit passes through a wall, the gap between the pipe and the edge of the wall opening needs to be sealed airtight with a flexible adhesive sealant. These penetrations are often neglected for two reasons: 1) the flawed assumption that small holes can’t compromise the acoustical effectiveness of a heavy wall or slab, and 2) the misunderstanding that acoustical ceiling assemblies are as effective at blocking sound transmission as they are at absorbing reverberation.
Junction boxes for light switches and outlets, while they don’t constitute outright penetrations, can present weak spots in walls as well. Cracks and gaps around windows and doors, though subtle to the eye, can be equally damaging to the acoustical integrity of a building or room. When finding and sealing these weak spots, changes in temperature can be a dead giveaway. Because sound and heat are both types of energy, just about any strategy to reduce a building envelope’s thermal transmittance will also reduce sound transmission.
Similarly, because sound pressure energy travels at roughly 1,100 feet per second and in all directions, noise doesn’t just find the most efficient flanking path – it finds every flanking path. Understanding this fact can help determine which conditions are worthwhile to treat and, just as useful, which ones are not. For example, when trying to protect a classroom from corridor noise, it is not at all beneficial to seal wall penetrations above the ceiling unless it can be assured the teacher will close the classroom door. Sealing penetrations between adjacent classrooms may prove more effective.
Sheet metal ducts are designed for delivering hot and cold air over long distances, and because they have to penetrate walls, they can be just as efficient at conducting mechanical and other noise all over a building. It is often possible to replace small sections of ductwork with larger, acoustically-lined sections to reduce sound transmission between acoustically critical spaces in existing buildings.
Noise From Inside
It has been said that the quietest classrooms are those without children. While it may not be possible to prevent the sound that students generate, a room’s finishes can prevent noise from building up by reverberation. Whereas sound waves have to negotiate multiple reflective and absorptive surfaces – people, equipment, furnishings – before reaching the floor, nearly every square inch of a classroom’s ceiling is exposed to noise from below. For this reason, it is vastly more effective to use absorptive materials on the ceiling and upper wall surfaces. When acoustical tile is suspended from existing plaster ceilings, a classroom’s Reverberation Time is reduced in two ways: 1) from the introduction of absorptive material and 2) by reducing the room’s volume. Where existing ceiling heights prove restrictive, fibrous acoustical panels can be surface-mounted.
Soft flooring is also useful in buffering impact noise from upper floors, and can eliminate the grinding and squealing from desks and chairs moving across harder surfaces. Especially in early childhood environments, introduction of area rugs might offer a more economical, more flexible solution than fixed carpeting, but care should be taken to prevent tripping around the edges.
Room furnishings can sometimes offer as many opportunities for absorption as the walls themselves. In lieu of traditional base and wall cabinets, large wood cubbies with open fronts can be provided along an entire wall and fitted with heavy fabric flaps instead of doors. Each flap is fastened continuously along the top edge and held in place by magnets at the bottom corners. The effect is a reduction in auditory and visual noise. Similar heavy fabric treatments can be used to mask upper areas of window glazing, which can be just as problematic visually (from glare) as acoustically (from reverberation).
As they age, buildings can only get noisier, not quieter – cracks form and widen, duct anchors come loose and vibrate, fans and belts begin to squeal. Whatever the mix of exterior and interior noise, the best retrofit solutions are the ones that counteract multiple sources at the same time. Hiring a qualified acoustician who can help find those solutions is highly recommended, and can leverage all the other investments you make in an existing building.