Sound Plans For Open-Plan
In the '70s, the cubicle was king as companies discovered the benefits possible with open-plan design. Popping partitions between employees in a "bullpen" could boost efficiency without the expense of private offices. But, as many discovered, open-plan designs were as likely to be a flying success as a costly failure. Without proper attention to acoustical considerations, noise levels rose, productivity fell and employees became disgruntled. What was true then is true today: open-plan design requires thoughtful acoustical planning.
Who Needs Open-Plan?
Key to succeeding in open-plan design is knowing when and how to use it. Open-plan is ideally suited to increasing productivity where employees need to interact on a regular basis. In fact, contemporary open-plan can be defined as an area of work stations organized on the basis of communications flow between stations.
Obviously, open-plan designs won't be effective for certain types of employees. Managers, for instance, generally require enclosed offices for prestige and privacy. Engineers, and many design professionals, need ample wall space to hang drawings and may be better served with private offices. Creative personnel, such as writers, may require enclosed offices to eliminate distractions and maintain productivity.
Most often, an open-plan interior solution will incorporate some enclosed offices. Typically, the percentage of space that is actually open-plan is 40 to 60 percent. However, it is often best to limit open-plan to no more than 40 percent because, as the percentage of space devoted to open-plan increases, so do the complexity and cost of adjusting acoustical problems.
How Private is Private? A final test of whether open-plan design is appropriate is determining the exact level of privacy required between work areas. Acousticians divide privacy into five categories or "classes," ranging from Class I, confidential privacy, where speech cannot be followed with understanding to Class V, good communication, where there is no privacy, such as in an auditorium or conference room.
Open-plan design is ideally suited to areas requiring marginal privacy, where a relatively quite atmosphere is needed but speech privacy isn't a primary concern. Areas requiring confidential privacy or normal privacy, where speech can be understood only with careful listening, are more challenging to accommodate with open-plan design. An acoustical consultant should be involved in open-plan projects that require more than marginal privacy.
Screened and Not Heard
The single biggest problem in open-plan offices is noise, whether from copiers, telephones, printers, calculators, keyboards or people. The accompanying illustration shows paths by which sound travels from work station to work station. Absorbing those sounds before they have a chance to travel about the space is key to creating an environment that enhances productivity. A number of systems are typically used.
Perhaps the element most associated with open-plan design is the partitions used to separate spaces. Providing visual privacy, partitions also perform the more vital task of absorbing sound. They should have enough sound attenuation (measure by STC) to prevent sound from traveling through the screen and also be high and wide enough to block flanking sound paths. Partitions should also have sound-absorptive material on each side to reduce sound reflection. USG Interiors' Ultrawall is an example of an acoustical partition ideally suited to open-plan designs, as it can be used for both screens and full-height partitions.
Acoustical ceilings keep sound from reflecting down onto the work space so they need to be highly absorptive, as measured by NRC. Today, manufacturers offer a vast array of ceiling panels so that it is possible to find a high NRC product that complements the design scheme of any open-plan space. Take care with placement of light fixtures in the ceiling grid. Placed directly above a partition, fixtures can reflect sound from one area to another. Luminary placement is particularly critical in environments requiring confidential or normal privacy.
Carpeting can be useful in absorbing "surface noises" such as dropped items and footfalls. Carpeting alone, however, will not provide sufficient sound absorption for the open office. Just as standing on a sponge won't keep you from getting wet if a bucket of water is thrown on you, carpeting below won't impede sound originating at higher levels.
Draperies, too, are often overrated as a sound control solution. To prevent reflection off exterior walls, the drapes would need to be so heavy they would block light and would have to be kept closed. A more effective solution may be to plan enclosed offices along fenestrated walls, particularly if the walls are more than 40 percent fenestrated.
If You Can't Beat It, Mask It
An irony of open-plan acoustics is that when sufficient sound absorbing materials have been installed to effectively cut reflected sound, direct sound (sounds that are heard before they strike an absorbing surface) become a major distraction. Electronic masking systems are used to "hide" direct and unabsorbed noise.
Sound masking systems are essential in open-plan offices requiring high levels of speech privacy and where noise levels are especially high. The systems work not by eliminating noise, but by producing a sound of their own that masks distractive noises. In most offices, mechanical systems produce a masking effect. Sound masking systems are simply controlled background noise specifically engineered to suit a particular acoustical environment.
Typical sound masking systems consist of electronic equipment that generates the masking noise and loudspeakers, located in the ceiling plenum, that broadcast the noise about the space. The masking noise level and spectrum content (frequencies used to make the noise) are specially adjusted to suit the specific requirements of each installation. Foil-backed acoustical ceiling panels are generally used because their reflective ability helps to distribute the masking sound more evenly throughout the ceiling plenum and, subsequently, the office space below.
Professional Sound Planning
Because of their complexity, sound masking systems should only be developed by an acoustical consultant. In fact, an acoustical consultant can help ensure the success of virtually every open-plan design. Consultants are familiar with common and uncommon problems in open-plan design; they know the products available and the latest technologies. An acoustical professional can save money up front by selecting only the components that are really needed and by developing a sound control solution that works from day one.
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