Most evaluations of the acoustic environment focus only on the quantity, or volume, of sound. In doing so, noise control strategies are often pursued in the “Quest for Silence” – the notion that good acoustics are achieved when the sound levels in a space are as low as possible, with zero being the best. However, just as with ergonomic factors such as light, temperature, and humidity, there is a comfort zone for the volume of sound, and it is not zero.
The noise floor is the level of continuous sound that characterizes a space at any given time. To be heard, other sounds must rise above this floor. If the floor is too high, the environment will be irritating and tiring. If the floor is too low, conversations and noises can easily be overheard and become distractions, reducing productivity and increasing errors. While noises decay in volume over distance, a low noise floor also means that they can be clearly heard from afar. The noise floor in offices is often so low that voices carry intelligibly over a distance of 30 to 50 feet (9 to 15 meters) or more.
If the noise floor is too low, the dynamic range will often be too high. This term is defined as the variation in the volume of sound over time. Our senses are designed to detect such changes, and it is difficult to ignore them. Therefore, the higher the dynamic range, the harder it is to “block out” noise. Acoustic variations are also found across space, due to the mixture of building materials, the location of open air return grills, HVAC, and office equipment.
A masking system addresses these issues by distributing a background sound throughout the facility, raising the noise floor to a comfortable 42dBA to 48dBA, or higher where required. The system typically consists of speakers installed in a grid-like pattern above the suspended ceiling, which can also deliver paging and music signals. Many people still refer to masking as white noise; however, this term describes a very specific, and potentially irritating, type of sound used in early masking systems. When the masking spectrum has been properly engineered, the sound will be both effective and unobtrusive.
The masking system makes noises and conversations more difficult, or impossible, to hear or comprehend. It also reduces the dynamic range and minimizes the differences in the level and quality of sound across the space, making the facility appear quieter and movements from one area to another less disruptive. If the system is augmented by such strategies as including physical barriers and absorptive materials in the design, the result will be an even more comfortable and consistent acoustic environment.
A masking system should be used in both open and closed concept spaces. It is easily installed in existing facilities, providing an effective way to treat acoustic problems at nominal cost and without large-scale remodeling. Early incorporation of the system in a project can reduce costs by eliminating the need for extra insulation or layers of drywall, plenum barriers, and high-spec or permanent walls around private offices. In this way, masking also helps to maintain the flexibility of the space for future renovations and changes. In open plan spaces, masking can help maintain a level of acoustical control as density increases and workstation partitions become lower.
Niklas Moeller (firstname.lastname@example.org) is vice president at K.R. Moeller Associates Ltd., (www.logison.com), Oakville, Ontario, a manufacturer of soundmasking systems.