Evolution of sound masking in closed rooms

Photo © iStockphoto/lovro77

by Niklas Moeller
Typing the word “privacy” into a search engine yields a lengthy stream of entries describing the many ways in which privacy can be violated, including reports of hackers acquiring credit card information, law enforcement agencies mining social networking sites, and voice-activated electronics with the ability to eavesdrop on their owners.

The preoccupation with vulnerabilities exposed by the Internet and electronic products is understandable given their rapid spread into almost all aspects of everyday life. However, privacy can also be violated in “traditional” ways, and even by those who do not intend to infringe upon it. For example, people can be exposed to sensitive information simply by being within audible range of a conversation—an issue relevant to building design and construction, particularly for facilities where medical, financial, legal, or other confidential matters are discussed.

Constructing barriers
When attempting to create speech privacy for closed offices, organizations may specify walls with high sound transmission class (STC) ratings. However, these ratings are lab-tested and frequently overstate real-world performance by five to 10 points. Site-tested apparent STC (ASTC)—which takes into account all leakage paths, as well as the wall’s performance—or noise isolation class (NIC) ratings are better gauges, but unfortunately only testable after the fact.

Another common tactic is to construct full-height walls extending from the concrete floor and all the way to the deck. While this approach can increase isolation, it can also raise costs and reduces flexibility. Vigilance must still be maintained during design, construction, maintenance, and renovation to ensure penetrations in the walls’ structure are controlled, because even minor ones can substantially reduce acoustic performance. This level of care can be difficult to sustain over the life of the space.

In any case, modern design and construction standards do not always allow for a high level of physical containment. To preserve flexibility, walls are often built to the suspended ceiling or using demountable partitions. Walls may include substantial windows or even be built in glass from floor to ceiling. Budget can also limit options.

These challenges raise the question as to whether there are preferable and more reliable methods of achieving speech privacy for closed rooms, such as by incorporating sound masking technology into the design.

Speech privacy often proves elusive because of the many ways in which sound can transfer from one space to another. If the background sound level is lower than the sounds passing through a wall or via flanking paths, conversations can be overheard.
Photo © iStockphoto/MarcusPhoto1

Overcoming preconceptions
Over the last decade, there have been great advancements in the sound masking field, increasing performance, expanding functionality, and opening the door to new applications. Nevertheless, outdated design practices persist, often to the detriment of both speech privacy and acoustic comfort. One such custom is the exclusion of sound masking from closed rooms.

Several reasons are used to justify this type of design. The first is an historical remnant from the days when sound masking was first adopted to help with the acoustic challenges encountered in an ever-growing number of open plans. This initial application led some to conclude masking was only intended for these types of areas.

This opinion was reinforced by a significant technical impediment. Early sound masking systems typically used a centralized architecture, which is very limited in terms of its ability to offer local control over the masking sound. Large zones spanned numerous private offices and other enclosed rooms, with little opportunity to adjust the level within each space and no control over frequency. The resulting inconsistencies in the masking performance led vendors and dissatisfied customers to conclude the technology could not be applied in closed spaces.

Modern networked masking architecture addresses these historical objections by providing fine control over both level and frequency within small zones (i.e. one zone per closed office, and adjustment zones no larger than three loudspeakers, or 62.7 m2 [675 sf], within open plan), but some still argue closed rooms do not require sound masking because they are afforded sufficient speech privacy and noise control via physical isolation.

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