As building systems continue to evolve, noise remains the same—acceptable or annoying. The former often goes unnoticed and the latter requires attention. Noise is the number one occupant complaint in many projects. Various studies indicate that noise can negatively impact occupants by ultimately lowering productivity and increasing stress levels. This “invisible” problem is loud and clear.
By properly addressing all noise sources, offices can become more productive, conference room meetings more effective, and overall occupancy more comfortable. A firm grasp of the basics can go a long way towards achieving spaces that allow occupants to maximize the intended use, whether it be sleeping, working, learning, playing, praying, or eating.
The Characteristics of Sound
There are several acoustical characteristics that occupants typically notice when entering a space. The first is often background noise, that is, how loud or quiet a space is. Another is how reverberant a space is. When there are surrounding occupied spaces, the noise isolation (or lack thereof) provided by building assemblies can become apparent. While these metrics can directly impact the occupants, they can also influence the decision to rent or buy a building or space. Class A office space, for example, typically achieves lower background noise levels than Class B or C, which is one reason why it commands a higher price per square foot. Integrating acoustics into the client dialogue early helps optimize the design process and end result for everyone involved.
Noise can be thought of in three distinct aspects—source, path, and receiver. Every project has these three aspects, though they vary in number (one source vs. many) and importance (the receiver is an intern vs. the CEO). In many cases, noise control products can be applied to improve various conditions. A key identifier, and simple principle to always remember - is that sound can travel much like light. Go into a room, turn off the lights, and turn on the lights in the surrounding spaces. Wherever there is light, there is the potential for noise to leak.
Air transfer silencers can provide additional noise reduction to ensure that overall partition assemblies provide adequate noise isolation or speech privacy. For example, two adjacent rooms separated by a non-full height wall can be negatively impacted by noise flanking through the common ceiling plenum. As depicted below, this noise path can be reduced by using air transfer silencers at return grilles with the added benefit of reducing visibility into the plenum space. Projects often utilize non-full height walls between private spaces as a way to reduce cost. Unfortunately, if the resulting flanking path is not properly addressed, the relevant private space's effectiveness is also reduced.
Another common condition is when a full height wall (floor to deck) requires transfer air between spaces, but must maintain a specific STC rating. Mechanical room partitions, for example, are often designed to have a minimum STC-50 rating, but often also require penetrations for return air. One method for achieving both return air transfer and noise isolation requirements is to use a cross talk silencer, as depicted in the accompanying illustration. This product has lab-tested performance and can be sized appropriately to satisfy project design requirements.
Noise and light transmission are additional issues that are often overlooked during the design process. By addressing both of these issues, air transfer silencers allow for more flexible space layouts and mechanical equipment placement. They also can result in significant construction cost savings because of their simplified installation. Lined return boots are often recommended, but they have several drawbacks. For one, lined return boots are usually field fabricated with no reliable performance data. They also require additional labor due to support requirements and their height often limits installation especially in crowded or shallow plenum conditions. An air transfer silencer on the other hand can be installed directly below mechanical equipment in addition to having lab performance and minimal labor costs.
Solutions to most “noise problems” typically require the holistic evaluation of multiple paths with each requiring individual attention. By properly addressing noise issues, offices are more productive, conference room meetings are more effective, and occupants are more comfortable. All of the design criteria and terms described may not be directly relevant for every job, but each should be considered. Doing so will improve the end result, and provide more opportunity for project team integration throughout the building process. Most importantly, clients will be confident that all of their noise control concerns, not just the “usual suspects,” are addressed prior to construction. It is important to play an active role especially in areas where there is no clear owner. In many cases, this “gray area” occurs at mechanical and air distribution equipment “in” the occupied space, such as terminals and diffusers. Success is achieved when acoustics are prioritized. Clear communication between project team members on the desired acoustic environment and various available options lead to exceeding client expectations.