Impact on Communication

The fact that masking levels in private offices and other closed rooms are typically lower than in open areas helps address the two remaining objections.

First, the masking level in a private office will not interfere with communication inside the room itself. The volume of a typical voice is 55 to 65 dBA at conversational levels. The distance between two people talking in a private office is not sufficient for the masking to interfere with intelligibility.

Second, if the loudspeakers in a conference room are assigned to their own control zone and the masking is tuned to approximately 42 dBA, it will provide a measure of acoustic control while not conflicting with meeting room occupants’ communication requirements or the signal-to-noise ratio required for good microphone response during video or teleconferencing.

If a meeting or training room is actually large enough to allow the masking sound to impact occupants’ ability to communicate (i.e., over long distances), an in-room control also allows users to adjust the volume to a low enough level that voice clarity is restored, but overall sound quality is maintained. Though such occurrences are rare, they are not out of the question.

Success Stories

In practice, organizations designing with ceiling-height walls and sound masking have realized both their speech privacy, noise control, and cost savings.

In one example, the University of Southern California was struggling with how to achieve privacy between medical exam rooms in a health-care consultation center. With an open plenum, it attempted a number of successive design interventions to improve speech privacy. The addition of plenum barriers—effectively extending the walls to the deck above—did little to address the problem. According to Curtis Williams, vice president of Capital Construction, it was the addition of masking that “greatly reduced the intelligibility of conversations between the exam rooms, allowing patients and doctors to talk with peace-of-mind knowing that their discussions could not be understood in adjacent rooms.”

A major American health-care provider also recently changed its construction standards for medical office buildings away from deck-to-deck construction for similar reasons. After significant testing of mockup facilities, the company determined that it achieved as good or better speech privacy with ceiling height walls and sound masking. They reported cost savings of hundreds of thousands of dollars for a project of just over 30,000 square feet.

Special Considerations

There are cases where one may want to implement both deck-to-deck construction and sound masking; for example, in spaces where raised voices or high volume media will be used, as well as in areas with high security needs (i.e., that require confidential speech privacy). Also, if the facility features an open ceiling, full-height walls are recommended to ensure some degree of inter-zone isolation.

Of course, eavesdropping can also be intentional and handled in a much more sophisticated manner than leaning one’s ear against a glass and putting it up to the wall. Without the proper treatment, windows, doors, ducts, pipes, floors, ceilings, and walls also present opportunities for electronic forms of eavesdropping. Speech causes vibrations on these structures, which can be picked up by probes or microphones and translated into intelligible speech. These types of listening devices are difficult to detect because they can be used at a considerable distance from the target facility.

If an organization suspects that it might be subject to such a threat, a sound-masking system can be connected to transducers, which transfer the masking sound to the aforementioned physical structures, impeding the use of audio surveillance equipment. In this case, it is key to ensure that the system produces a truly random masking sound (i.e., rather than on a loop) so that it cannot be filtered out of recordings.

Retrofit Installation

If an organization moves into its facility and finds that the initial design or construction has failed acoustically, implementing sound masking might not be the only improvement necessary, but the only feasible choice.

First, budget pricing for a sound-masking system is low, particularly relative to other acoustical treatment (typically $1 to $2 per square foot, depending on project conditions). A separate paging and background music system is not required because most masking systems provide these functions over the same set of loudspeakers. Contemporary systems require minimal space for below-ceiling equipment. The additional electrical load and cost of operation are also negligible. Owners can relocate the system to future facilities, extending its useful life for the organization.

Second, sound masking is typically less disruptive to apply to an already-occupied workplace than other treatments. For example, installing a suspended ceiling in an occupied space involves not only the cost of the tile, but modifications to the lighting, HVAC, sprinkler system, and more. Furthermore, certain acoustical interventions may not be possible to implement in some facilities due to the structural changes involved (e.g., historic properties) or the noise and operational disruption that accompanies their installation (e.g., hospitals).

By comparison, sound-masking components are small and the installation process tidy. They can typically be installed without conduit in most jurisdictions. The work can be handled discretely after hours or with only minor temporary local disruption to occupants during regular hours. It usually proceeds quickly as well, further minimizing the impact on an organization’s operations. There are few requirements for power tools, making the work relatively quiet, and unless the ceiling is unusually high, only ladders are needed to gain access.

Third, as outlined above, sound masking can not only be used to improve acoustics in open plans, but to increase privacy for closed spaces, such as private offices and meeting rooms. Unlike closing the ceiling or extending walls to the deck, masking has no impact on other building systems. It also continues to function when the room’s door is open and the acoustical isolation it provided virtually disappears.

There are some implications of retrofitting a sound-masking system rather than including it in the original design. The cost to install may be slightly higher than in new construction due to the increased labour requirements. More importantly, by waiting to install masking post-occupancy, an organization may forgo opportunities to reduce construction costs or the requirements for other acoustical treatments. As discussed, 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.

In retrofit situations, it is also essential to select a masking system that offers a ramp-up feature. It slowly introduces the sound beginning at a level near the existing ambient volume, allowing occupants to gradually acclimatize to their new acoustical conditions. Over a short period of time, the sound becomes a natural part of their environment. In fact, if handled after hours, occupants are often unaware that the system has been installed. Full effectiveness is achieved once the masking sound has reached its final level.

In Conclusion

Building cost-effective and flexible closed spaces for true speech privacy can be challenging. However, combining physical barriers with sound masking can ensure effective results, while helping to control the cost of initial construction and future changes.

Indeed, the debate over whether sound masking should be included in closed rooms should be put to rest. In almost all situations, it is better to combine a reasonable amount of isolation with a raised ambient level, allowing companies to save on wall construction by reducing the STC ratings of walls and using floor-to-ceiling rather than deck-to-deck construction.

As long as the system is properly engineered for this type of environment, it is possible to provide the client with a suite of acoustic benefits that could not otherwise be achieved in private offices and other closed spaces, and also prevent the noticeable voids in the background sound level that are created when masking is only applied to open plans.

Niklas Moeller is vice president of KR Moeller Associates Ltd., manufacturer of the LogiSon Acoustic Network. He has more than 25 years of experience in the sound-masking field.

Today’s interiors are even more dependent on sound masking for speech privacy and noise control. The LogiSon Acoustic Network is tuned using TARGET, an application that accurately adjusts each small zone to the specified spectrum, maximizing benefits and occupant comfort. Worldwide distributors provide turnkey services and support. www.logison.com