Retrofitting Sound Masking: Improving speech privacy and noise control in occupied spaces

by Niklas Moeller, MBA
In recent years, many methods of providing speech privacy and controlling noise have been systematically eliminated from workplace designs. For example, closed rooms are increasingly built using demountable partitions, reducing room-to-room isolation. Despite rising occupant densities, workstation panels are often lowered or dispensed with altogether, harkening back to pre-1950s open plans. Absorptive finishes are forgone in favor of exposed concrete, metal, and glass, allowing noises to travel further and remain loud.

Whether these decisions are made for aesthetic reasons, to help achieve green or short-term budget goals, or in the name of the latest trend—‘collaboration’—they ultimately impact a facility’s acoustic performance.

However, an organization may not fully understand the degree of disturbance such design choices can cause until they move into their new facility and the complaints begin. Employees may express dissatisfaction with being able to hear people talking, as well as concern over their own level of speech privacy. Additionally, they may be frequently disrupted by noises such as ringing telephones, mechanical equipment, exterior traffic, and footfall.

A lot of effort goes into planning other aspects of a new facility, and it likely exhibits many desirable features, but an organization is then faced with the troubling realization people are having difficulty working in it.

If the organization had considered acoustics from the start, they would have had the opportunity to apply all the techniques required for an optimal result (see “The ABC Rule”), and likely realized construction and material savings in the process. However, at the completion stage, they typically need to adopt solutions offering the greatest opportunity for improvement while creating the least upheaval in an already-occupied environment. One such solution is a sound masking system.

Sound masking technology
Sound masking technology consists of a series of loudspeakers, that are usually installed in a grid-like pattern in or above the ceiling, as well as a method of controlling their zoning and output. The loudspeakers distribute a comfortable, engineered sound, raising the facility’s ambient—or background—sound level.

Adding more sound to a space runs contrary to most people’s understanding of how to achieve effective acoustics. Indeed, many believe the goal is to make the facility as silent as possible. However, due to improvements in construction materials, as well as quieter office and mechanical equipment, the ambient level in the majority of commercial offices is already too low. Employees working in these library-like environments are disturbed by even low-volume noises and can easily hear conversations occurring from as much as 15.24 m (50 ft) away.

By raising the ambient level, masking covers up noises lower in volume. It also reduces the disruptive impact of those that are higher by decreasing the magnitude of change between the baseline volume and any peaks in the space. Conversations are either entirely masked or their intelligibility is reduced, improving occupants’ privacy and further decreasing the number of disruptions to their concentration. The overall result is occupants perceive treated spaces as quieter.

Retrofitting options
There are numerous factors making retrofitting this particular acoustic solution attractive.

Budget considerations
Budget pricing for a sound masking system is low, particularly relative to other acoustical interventions, such as adding significant additional absorption and upgrading physical barriers. It is typically $11 to $22/m² ($1-2/sf), depending on project conditions. A separate paging and background music system will not be 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.

Application in open and closed spaces
Many people recognize sound masking is necessary to providing acoustic control in open plan spaces. However, it is also an easy and cost-effective method of increasing privacy in closed offices and meeting rooms.

Unlike closing an open ceiling or extending walls to the deck, masking has no impact on other building systems. Masking also continues to function when the room’s door is open and the acoustical isolation it provided virtually disappears.

Furthermore, because sound masking works ‘at the ear of the listener,’ it is also effective against noises or conversations regardless of how they find their way into the room and may, therefore, eliminate or reduce the need to address other acoustical pathways between spaces (e.g. sealing gaps between the walls and window mullions). This quality also makes sound masking a potentially effective tool against noises originating from outside the building. Whereas the building shell may not completely block the noise of traffic or passing aircraft, a masking system often easily covers these sounds or lessens their effect on occupants.

Ease of installation
Sound masking is typically less disruptive to apply to an already occupied workplace than other acoustic treatments. For example, consider the impact of building walls or increasing the height of workstation partitions in order to improve physical isolation. Adding significant absorption post-construction can also be challenging, depending on whether a suspended ceiling has to be installed or upgraded, or if acoustical panels need to be added to the deck, walls, or workstation partitions. Installing a suspended ceiling in an occupied space featuring an open deck involves not only the cost of the suspension system and finish materials (e.g. panels, tiles, linear metal).

In some facilities, such as historic properties, the tenant may be prevented from making these types of changes. For instance, they may not be permitted to upgrade windows to better block exterior noise, modify the ceiling, change the flooring, or move interior walls. In these situations, masking may be an option, though unique installation methods (i.e. where to locate loudspeakers) may need to be investigated.

Other facilities may not be able to endure the operational disruption accompanying some solutions. In hospitals, for example, it is next to impossible—and certainly undesirable—to shut down a fully functioning wing in order to effect changes in physical construction. Furthermore, the construction noise would disrupt patients and staff in adjoining spaces. Other facilities operating 24-hours a day, such as call or command centers, may have similar restrictions on retrofit construction remedies.

Whereas the installation of almost any other acoustical treatment may impact a large area of operations, sound masking components are small and the installation process tidy. These systems typically operate on Class 2 low-voltage power and can, therefore, be installed without conduit in most jurisdictions.

There are various loudspeaker types to suit a wide range of environments, including above-ceiling, ceiling plate, and wall mount. A creative provider can engineer a solution for even the most complex retrofit situation. The system generally has no visual impact on the space’s design because the loudspeakers are installed above the suspended ceiling. However, even in open ceiling spaces, the loudspeakers and equipment are discrete and, in certain cases, attractive.

Minimal disruption
The work can be handled discretely after hours or with only minor temporary local disruption to occupants during regular hours. The work usually proceeds quickly as well, further minimizing the impact on an organization’s operations. For example, while installation time varies according to site conditions and crew size, a typical 1393-m² (15,000-sf) office floor with a typical suspended acoustical panel ceiling can be installed in a single night, after hours. Some types of installations may take longer. For example, if there is no suspended ceiling, cabling needs to be handled according to aesthetic considerations, which can be more time-consuming. In areas with gypsum ceilings, more loudspeakers are needed for uniform coverage and the installation time will be longer due to the need to make ceiling cut-throughs for the loudspeakers and run cables through a confined space.

Retrofitting a masking system in a facility operating 24-hours a day presents an additional hurdle, but is generally also achieved with minimal disruption. In a hospital setting, a system may be installed in, at most, one to two hours per patient room, after which the room can be immediately occupied. 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.

 Retrofit implications

There are some implications of retrofitting a sound masking system rather than including it in the original design.

First, the cost to install may be slightly higher than in new construction due to the increased labor requirements necessary to gain access to the closed ceiling, work around furnishings, and potentially work after hours.

Second, by waiting to install masking post-occupancy, an organization may forgo opportunities to reduce construction costs or the requirements for other acoustical treatments. For example, when designing with a masking system, many organizations find they are able to build walls only to the suspended ceiling rather than deck-to-deck, reducing costs and maintaining the flexibility of the space for future renovations. The project team might also make different choices with respect to ceilings when planning with masking. Neither of these decisions can be revisited post-construction. Most systems also provide paging and music functions, eliminating the need for a second system to be installed.

Third, if adding sound masking to a less than ideal space—in other words, one that does not feature sufficient physical barriers and absorptive materials—occupants will still have to reconcile themselves to having less than the best possible acoustical performance in their space. Masking is not a silver bullet. Though it reduces the requirements for other treatments, a balanced approach to acoustic design is always needed.

Sound masking will not have the same impact as a physical barrier on noises produced at short distances, and it will not reduce reverberation like absorptive materials. Thus, the overall acoustical performance will not be what it could have been if acoustics were addressed at the design stage.

In retrofit situations, it is also essential to select a masking system offering a ‘ramp-up’ feature. This means it can slowly introduce the sound beginning at a level near the existing ambient volume, allowing occupants to gradually acclimatize to their new acoustical conditions. Full effectiveness is achieved once the masking sound has reached its final level.

Acoustic network case study
In 2012, a biotechnology company based in the San Francisco Bay Area experienced speech privacy issues in two of its existing facilities. One office occupied two buildings, each with four floors, while the second extended over two floors in another building—totalling 23,225 m² (250,000 sf).

Solution
The biotechnology company approached consultants Charles M. Salter Associates for advice. The principal consultant, Ethan C. Salter, evaluated the space and determined part of the issue was the existing environment was too quiet, which allowed adjacent people to overhear those nearby, causing distraction and complaints. Indeed, tests of the existing conditions showed speech privacy between spaces was less than the company’s goals.

Due to the project’s large size and different areas of concern—including private offices, training rooms, and open plan—Salter determined a sound masking system both flexible and uniform was required to meet the company’s goals.

Salter established the sound masking specifications necessary to ensure system performance and the sound masking system was subsequently installed in both buildings in late 2012 and early 2013.

The two projects included approximately 1200 loudspeakers and featured the system’s localized control capabilities. Sound masking adjustment zones were no larger than three loudspeakers—approximately 67 m² (675 sf)—and each provided a local masking sound generator, volume control, and third-octave equalizer for frequency control. Volume controls were provided in half decibel increments and equalization from 63 to 10,000 Hz.

The design included sound masking in both the open and closed spaces. In closed rooms, the masking offered several advantages. First, it increased speech privacy between rooms and to the outside. Second, it reduced the apparent audibility of noise in the rooms, both with the doors open and closed. Third, it established greater consistency in the background sound levels in the open plan and closed rooms, avoiding a sudden and noticeable shift in ambient sound levels.

The specified sound-masking system was installed by an electrical contractor. It was handled during the night over the course of a few weeks, without disruption to the client.

Following installation, the system was commissioned in conjunction with Salter, during which time local adjustments were made to ensure it conformed closely to the desired masking levels throughout.

Results
Post-construction acoustical testing data showed the company’s goals for privacy were achieved with the addition of this flexible sound masking system. The client was pleased with the results and has since incorporated the same system into several buildings during construction.

Conclusion
Sound masking is easy to retrofit. In some cases, it will not be the only improvement necessary to correct deficiencies in acoustical performance; however, in others, even when the ideal solution includes various approaches, sound masking will be the only feasible or acceptable answer for the reasons outlined in this feature.

Niklas Moeller is vice-president of K.R. Moeller Associates Ltd. (Burlington, Ont.), a global developer and manufacturer of the sound masking system, LogiSon Acoustic Network. He writes a weekly acoustics blog, www.soundmaskingblog.com. He can be reached at nmoeller@logison.com.