Achieving Effective Acoustics

To create an effective work environment, acoustic professionals typically take a three-pronged approach that involves absorbing, blocking and covering noise. Because all three strategies are required to achieve the best results, they are collectively referred to as the “ABC Rule.”

Today, the term “collaboration” is often invoked to justify the elimination of many elements of this time-honored rule, but reports such as Gensler’s “What We’ve Learned About Focus in the Workplace” (2012) show that most employees still spend more than half their time on individual work that requires concentration. 

In addition, research such as the Lewis & Clark State Office Building Post Occupancy Evaluation (2008) conducted by Sue Weidemann of CP & Associates indicates that employees spend a further 20 percent of their time on the phone or in conversation at their workspace. Rather than benefiting from overhearing each other, the Center for the Built Environment (CBE) found that the majority of employees consider it irritating and disruptive. They are also concerned by their lack of speech privacy. A review of the ABC Rule seems timely. 

Absorb Noise

“A” stands for adding “absorption,” which reduces the energy and, therefore, the volume of noises reflected off various surfaces back into the space, the length of time they last and how far they travel.

To meet this requirement, it is important to invest in a good acoustic ceiling tile and ensure consistent coverage throughout the facility. Also, limit the lighting system’s impact on the ceiling’s performance by selecting an indirect system that incorporates a minimum number of fixtures while still meeting the lighting requirements. Minimize the use of hard materials, such as glass and metal, because these reflect noise and conversation, causing them to be heard over greater distances. Use absorptive partitions, at least inside and above the work surface, and install soft flooring in high-traffic areas.

Block Noise

“B” is for “blocking.” Closed rooms use walls and doors for this purpose, but blocking is also a relevant technique for open plans. 

For example, one can locate noisy office machines and high-activity areas, such as call centers, in remote or isolated areas. Also, maximize the distance between employees and minimize direct paths of sound transmission from one person to another by seating employees facing away from each other on either side of partitions. Note that partitions that are 60 to 65 inches (1.5 to 1.65 meters) are effective because they extend beyond seated head height. Using taller partitions in high traffic areas can be beneficial.

Cover Noise

“C” stands for “covering up” unwanted noises by providing an appropriate ambient – or background – sound level, which is typically between 42 and 48 dBA in commercial interiors. This requirement is met by installing a sound masking system.

This technology consists of a series of loudspeakers installed in a grid-like pattern above the ceiling, which distribute a sound most often compared to that of softly blowing air. Though the sound is audible, occupants perceive treated spaces as quieter because raising the background sound level reduces the intelligibility of conversations and the disruptiveness of noises (i.e. either by covering them completely or by reducing the magnitude of change between the baseline and peak volumes in the space). The sound’s efficacy is increased by virtue of being specifically engineered to mask the frequencies in human speech. It also creates a more consistent acoustic environment by minimizing variations in sound quality across the facility.

Reduce Noise

Though not included in the ABC Rule, noise reduction is also key to achieving effective acoustics. It involves removing noises that simply do not need to be there, such as those caused by improperly designed or balanced ventilation. Etiquette is also part of this strategy; for example, using a reasonable voice level within an open plan. However, occupants always generate noise as they work. So, while behavior modification is helpful, the remainder of the acoustical burden has to be borne by design.

A Powerful Combination

Each of these methods contributes differently to overall acoustic performance. Therefore, they are most powerful when used in combination and the root of any problem usually lies in the omission of one or more of these methods or their imbalanced application. 

More often than not, the missing element used to be “Cover” because many held the mistaken belief that acoustics would only be under control when their space was as silent as possible. Today, “Absorb” and “Block” are also often omitted. The percentage of open plan space has grown and occupant densities have risen. Also, partitions have lowered or disappeared, and the use of absorptive finishes has diminished, allowing noises to travel further and last longer. Closed rooms are increasingly built using glass walls, walls that stop at the ceiling or demountable partitions, reducing room-to-room isolation. Whether done in the name of collaboration, short-term budget concerns, sustainability goals or aesthetics, the impact on acoustics is undeniable.

If the organization moves into their facility and finds that the initial design or construction has failed acoustically, implementing “Cover” might not be the only improvement necessary, but the only feasible choice. Budget pricing for sound masking is low relative to retrofitting other treatments and post-occupancy installation can be handled with only minor disruption. In addition, this technology can not only be used to improve open plan acoustics, but also to increase privacy for private offices and meeting rooms. Unlike closing the ceiling or extending walls to the deck, adding masking will have no impact on other building systems.

That said, it is always preferable to plan for acoustics during the design phase and take full advantage of the ways in which the various acoustic treatments can complement each other. For example, high spec walls and plenum barriers can be replaced by a combination of floor-to-ceiling walls and sound masking, achieving the same or better privacy while reducing the cost of initial construction and future changes. Implementing the ABCs from the outset allows one to help to protect an organization’s greatest asset: employees.  

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