Evolution of sound masking in closed rooms

Providing occupant control
Often, it is practical to include an in-room control permitting occupants in private offices and meeting rooms to regulate the masking level, as well as paging and background music. While such individual control is undesirable in shared, open plan areas, closed rooms should afford a measure of personal control. (It is important to note the masking level in a private office does not interfere with communication inside the room itself. The level 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.)

In-room control can be provided via hardware, such as a programmable keypad or rotary volume control, a software application, or integration with third-party equipment. However, when such controls are offered, there are additional functional considerations. For instance, the user should not be given unfettered control over the masking level. If an occupant is allowed to mute or lower the volume beyond a certain limit, others’ speech privacy suffers. Also, frequency control should not be included because the user has neither the tools nor the training required to make informed adjustments to the masking spectrum.

If occupants are given control in closed rooms that are shared, such as meeting or conference rooms, then it may also be desirable to have those user adjustments reset automatically at certain times, restoring masking and paging levels to default settings. (If the loudspeakers in a conference room are assigned to their own control zone and the masking is tuned to approximately 42 dBA, it provides a measure of acoustic control while not conflicting with 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], installing an in-room control allows users to adjust the level to a low enough volume so that voice clarity is restored and overall sound quality is maintained.)

Success stories
In practice, organizations designing with ceiling-height walls and sound masking have realized both speech privacy and cost savings goals.

For example, the University of Southern California was struggling with how to achieve privacy between medical exam rooms within a healthcare consultation center. With an open plenum, they 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.”

After testing mock-up facilities with ceiling-height walls and sound masking, a major American healthcare provider also changed its construction standards for medical office buildings. They reported cost savings of hundreds of thousands of dollars for a project of just over 2787 m² (30,000 sf), while achieving as good or better speech privacy as deck-to-deck construction. (There are some cases where one might want to implement both deck-to-deck construction and sound masking. For example, spaces where raised voices or high-volume media will be used, as well as areas with high security needs. Also, if the facility features an open ceiling, full height walls are recommended to ensure some degree of inter-zone isolation.)

Conclusion
Closed offices and meeting rooms are built with the intention of providing occupants with both visual and acoustic privacy. While the first goal can easily be achieved, the latter often proves elusive because of the many ways in which sound can transfer from one space to another. Speech privacy levels fluctuate from wall assembly to wall assembly, depending on their performance in the frequencies used to calculate STC, as well as the inconsistent noise levels and spectrum generated by HVAC—not to mention sound leakages through various flanking paths such as gaps along the window mullions, ceiling and floors, as well as through the plenum, ductwork, return air grills and, of course, open doors. Each crack in a wall’s armor facilitates the transmission of sound to and from neighboring spaces. Ultimately, the lack of sufficient background sound allows conversations to be overheard.

Combining physical barriers with sound masking can ensure effective results while helping to control the cost of initial construction and future changes. In most situations, sound masking provides not only cost and flexibility advantages, but also as good or better speech privacy as deck-to-deck construction. Further, with sound masking, one has the opportunity to increase the background sound level in the event a partition does not perform to spec and remedial action would be cumbersome and/or costly—a flexibility uniquely afforded by this technology.

Niklas Moeller is the vice-president of K.R. Moeller Associates Ltd., manufacturer of the LogiSon Acoustic Network (logison.com) and MODIO Guestroom Acoustic Control (modio.audio). He has more than 25 years of experience in the sound masking field. Moeller can be reached at nmoeller@logison.com.