Shen Milsom & Wilke
Sound masking is an effective tool for enhancing speech privacy and reducing distraction, but how does it work?
Let’s first discuss noise cancellation. Noise cancellation is technically when a sound pressure wave, which has peaks and valleys in pressure, is cancelled out by an out-of-phase (or opposite) sound pressure wave. As this suggests it’s a very precise and controlled operation to cancel a sound pressure wave. It requires a very controlled environment and specific sampling and reproduction of the sound source. Noise cancellation works within the controlled environment of headphones, within car/truck cabs, and for large exhaust stacks; very defined environments. Office areas are not controlled and defined environments.
Sound masking, “masks” or covers-up other sounds. Thus, it is sometimes referred to as “Acoustic Perfume.” Sounds at lower or equal levels are fully or partially covered-up or masked, and thus, those sounds are inaudible or only partially audible. Since the “perfume” covers-up some sound, the remaining sounds and voices become less distracting and in some cases are covered-up enough to provide a good degree of speech privacy. The presence of a moderate background sound level, provided by sound masking, also reduces the tendency to listen for other sounds.
Today’s open plan office environment, with low furniture systems, high density and the desire for instant collaboration, can use sound masking to reduce distractions from remote sources and activities. The old-time design of 60+/- inch high acoustic screens and 12+/- ft. between workers would provide a fair to good degree of speech privacy when coupled with sound masking. But, today’s “iPod” generation (ear-buds constantly on) demand an open, day-lite, collaborative environment. With that environment, office activity and remote voices become clearly audible and distracting. You expect to hear and collaborate with persons within your immediate vicinity, but not necessary persons 30+/- ft. away. Sound masking reduces your “exposure” to the immediate area and reduces distractions and disturbances from remote areas.
In one open office environment without sound masking, main complaints are “it’s too noisy” and “it’s too quiet.” It turns out these are the same complaint. Without masking, general office activity and voices seem too “loud,” while at the same time, without masking it was too “quiet” so remote activities and voices are easily heard. Both complaints relate to being disturbed or distracted by remote activity and voices. Once sound masking is added to the environment, complaints regarding distractions and disturbances greatly reduce.
For enclosed offices and conference rooms, speech privacy can be enhanced, and money can be saved in construction when implementing sound masking. Privacy is achieved when the transmitted voice is mostly unintelligible. To achieve this, the transmitted voice must be generally below the background sound within the receive/listening space. When the background sound is very low, you can hear a “pin drop” in the adjacent space. When sound masking is properly implemented, the background sound is slightly elevated and specifically tuned to help cover-up or mask transmitted voices.
Acoustic Privacy
Various degrees of speech privacy can be achieved with only the separating construction (no sound masking) when using full-height multi-layer insulated drywall partitions; which is typically desirable for high-profile audio/video related conference rooms, executive offices, HR and legal departments. However, for typical enclosed offices, meeting rooms, and manager level offices, sound masking can be used in conjunction with lesser demising construction to provide a “normal” level of speech privacy. A “normal” level of speech privacy is generally when normal voice levels can be heard, but there is minimal-to-no context of conversation. Of course, there are always people with unique sensitivities to sound/noise, louder “normal” speaking tones, and speakerphone use that may not be adequately addressed with sound masking.
Along with proper acoustic door seals, sound masking can also be used outside of rooms where private conversations may take place and improved speech privacy at the door is needed; such as medical exam and consultation rooms, counseling offices, boardrooms, courtrooms, etc. Sound masking is commonly used in courtrooms so judge-counsel conversations at the bench are not overheard by others.
A sound masking system typically consists of an array of loudspeakers above the ceiling (out of sight) controlled and powered thru an interface positioned on the wall in a local low-voltage room. The price can vary based on size of system, as well as field and labor conditions.
Overall, sound masking (acoustic perfume) can be an asset on a project to improve privacy, reduce distractions and save construction costs. Reducing distractions increases productivity, thus sound masking provides further monetary benefit for the end users.
James Merrill is a partner at Shen Milsom & Wilke, Princeton, N.J.
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