Can You Hear Me Now?

Sound — it shapes how people perceive the world, and plays a vital role in communications and education. Schools depend on designers and architects to understand the science of sound — acoustics — and to do a good job of managing sound within a structure. But today's world and the structures being built can make this task challenging.

Background noise

Background noise is one obstacle affecting acoustics. It can come from a variety of sources inside and outside a space. Even a vacant building is not silent. Computers, copiers, lights, vending machines and refrigerators contribute noise. The noisiest offender often is heating, ventilation and air-conditioning (HVAC) equipment.

The HVAC system's effect on a building's acoustics may be overlooked during design because the systems are already a significant building cost, and schools are reluctant to direct higher percentages of budgets away from areas that do not benefit student learning directly. A silent HVAC system can be designed, but it is an intentional design. Silencing the system involves specially insulated equipment, heavier units to deaden fan noise and larger ductwork to permit the easier flow of air.

Activities in adjacent spaces also can contribute to background noise: exterior sources such as nearby roads, railroads or industries, and internal sources such as other classrooms, band rooms and offices.

The big space challenge

In addition to managing background noise, acoustic designers must consider another key contributor to the acoustics challenge: reverberation. Reverberation is the time it takes for sound to fade or decay in a space. Large rooms where people congregate present a considerable acoustic challenge.

A typical college student center has dining and food-preparation areas, as well as general space where students congregate, so there's a lot of noise generated by both people and machinery. In a space like this, sound-absorbing material is important with consideration to maintaining the space's aesthetics and durability. Sound-absorbing materials often are part of the decor of the space, adding colors and textures to create inviting spaces.

It's also important to look at sound transmission with regard to adjacent spaces. For example, offices that are near large, open spaces not only have to be protected from unwanted sound entering, but also must keep sound — and private conversations — from escaping.

Sound transmission across these boundaries must be controlled through proper construction of the walls and openings. Walls should be extended to, and sealed to, the structural deck, and insulation placed in the ceilings. Staggering studs and the use of sound-attenuating insulation also will help block sound. When special attention is paid to walls and ceilings, then doors, windows and electrical outlets often become the weakest elements through which sound will still pass. The careful arrangement of these elements in a space plan, such as staggering door openings in a hallway, isolating noisy spaces such as gymnasiums, and ensuring that electrical outlets are not placed back-to-back, can help. Uniform building code (UBC) requirements may not be adequate to block sound — or optimize acoustics — in any space. If blocking sound is a key concern, consider the need for all materials in a space to carry a high sound transmission class (STC) rating, or insulation quality.

Often, large spaces have conflicting acoustical needs. A chapel or performance hall, especially where there will be classical music, needs a “live” acoustical quality. That means the room must be designed so sound can reverberate. However, reverberation can interfere with speech intelligibility — long reverberation times can cause a speaker's words to be muffled, so that one word cannot be distinguished from another. An ideal space for speech has low reverberation, called “dead” or “dry.”

Reconciling these acoustical opposites often is done with sophisticated sound systems. A space designed as a live space can incorporate a well-designed sound system to create the sound clarity needed for quiet events or speeches. Because the number of attendees also can affect acoustics, consider using absorptive seating to maintain a consistent acoustical environment.

School gymnasiums usually are large, rectangular boxes with hard-surface walls, floors and ceilings. The elements make a highly reverberant space where teachers can have a difficult time making themselves heard — even when students are paying attention.

The most common solution is to add sound-absorbing material to the space, like acoustical block for walls or a layer of sound-absorbing panels over hard walls. Sound-absorbing materials installed on non-parallel surfaces will lower reverberation and make a space quieter. For good speech intelligibility in these larger rooms, sound designers will recommend installing a wall absorber with high sound absorption on the rear wall. Also popular is acoustical decking, which is a type of under-ceiling with perforations and sound-absorbing material. Selecting durable acoustic materials that will withstand the impact of kicked and thrown balls is a key consideration for multipurpose rooms used for sports.

First things first

Mistakes with a room's acoustics happen when a facility's design does not account properly for the acoustics. Sound-design experts start by thinking about the acoustics of a space before any lines are drawn on paper. They consider the intended use of each room or area, and determine an acceptable reverberation time and design. This information is shared with the building designers to create the design of individual rooms, as well as where each room should be situated within the facility.

Even spaces with similar uses may need different reverberation times and different materials to handle the sound. For example, band rooms and choral rooms sometimes are given the same acoustical treatment, but this may lead to problems with volume and speech intelligibility.

Multipurpose rooms are an economic reality in many schools. The best approach is to determine the most common use and to design the reverberation time for those needs. Most often, the need for quality, intelligible sound for instruction is paramount, so here the multipurpose spaces may be designed as “dead” spaces, and hard surfaces can be brought in when a higher reverberation is required.

Although cost containment is a reality in building projects, skimping on acoustics almost always costs more in the long term. Spaces that are not designed properly for their uses may be retrofitted; however, the cost to do so often is higher, and the results rarely are what they could have been if accommodated for during design. An acoustic treatment may be suitable for the present application, but the constantly changing uses in a facility can quickly change the picture.

Sterner, PE, is president of High Construction Company, Lancaster, Pa. The firm specializes in design-build, general contracting and construction-management services.

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