Web Exclusive Q&A: The Evolution of Sound Masking

Moeller

As open plan offices grow increasingly common, so does the need for strategies to lessen noise from office activities. Sound masking systems distribute background noise via loudspeakers and help control acoustics. Niklas Moeller, vice president of K.R. Moeller Associates Ltd., explores advancements in the technology behind these systems and how to achieve acoustic control and occupant comfort.

Why is the use of sound masking on the rise?

Research has raised our awareness of the impact of poor acoustics on productivity and workplace satisfaction. Most employees spend over half their time on individual focus work and another large percentage on the telephone. Their environment should support these activities, but trends in workplace design—open plan space, modular walls, higher occupant densities—make it acoustically challenging. Masking controls the ambient—or background—sound level, covering up conversations and noise or reducing their disruptive impact by decreasing the amount of change between the baseline and volume peaks.

Why is controlling the ambient level necessary?

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 facilities is already too low, leaving employees trying to work in ‘pin-drop’ conditions in which they can easily hear conversations and noises, even those generated at a distance or relatively low in volume. Sound masking replenishes and maintains the ambient level, helping to control acoustics in much the same way as temperature and lighting.

Can sound masking only be used in a new build?

Masking is easy to retrofit, but it shouldn’t be relegated to ‘band-aid’ status. If included in the design phase, you can reduce the specs for other acoustic treatments and often use floor-to-ceiling rather than slab-to-slab construction for private offices and meeting rooms. Masking typically adds 5 to 12 dBA of ambient volume to these spaces, which is why it’s said to add 10 sound transmission class (STC) points to walls. In retrofit situations, a masking system might not be the only improvement necessary, but the only feasible choice. Cost is low relative to retrofitting other treatments and post-occupancy installation causes only minor disruption.

Large zones require compromises to be made between masking effectiveness and occupant comfort. The larger the zone, the more people affected by those compromises. As masking technology evolved, zone size shrank to one to three loudspeakers, providing localized control over the sound’s volume and frequency.

KR Moeller Associates Ltd.

Is sound masking the same as white noise?

‘White noise’ and ‘pink noise’ are often, but mistakenly, used to refer to sound masking. Unlike these particular colors of sound, masking follows a non-linear curve specifically designed to balance acoustic control and occupant comfort. This target curve should be set by an acoustician or a third party such as the National Research Council, rather than by the manufacturer. The typical range is between 100 to 5,000 hertz, but may go as high as 10,000 hertz. While listeners describe white noise as hissy, most compare the sound of a professionally-designed and tuned masking system to softly blowing air.

How is the sound masking curve achieved?

No masking system achieves the target curve out of the box. Regardless of its design, where its loudspeakers are located or whether they face upward or downward, the sound changes as it interacts with various interior elements, such as the layout and furnishings. To meet the curve, an acoustician or technician measures the sound at ear height, examines the results, and adjusts the system’s volume and frequency settings accordingly. They want to keep variations in the sound to a minimum because these impact masking performance and occupant comfort. That’s why a specification typically includes a tolerance, indicating how much the sound is allowed to deviate from the curve across the treated space. You want to ensure the sound provides the intended benefits and they are enjoyed equally by all occupants.

A sound masking spectrum, or ‘curve,’ should be specified by an acoustician or supplied by an independent party such as the National Research Council (as shown).

KR Moeller Associates Ltd.

Have there been any significant advances in the technology?

Masking systems have actually been in use since the 1960s. The earliest used a centralized architecture, which assigns areas to general categories—for example, open plan, closed room and reception—based on the belief they have the same or similar acoustics. Each one is covered by a single zone comprised of a large number of loudspeakers, limiting local adjustment. In the 1970s, decentralized architecture reduced zone size to a maximum of three loudspeakers. Volume and frequency can be adjusted where needed, without affecting large areas. In the early 2000s, engineers took this approach further, making system components addressable within a networked architecture. Networking permits changes to be made from software, as well precise computer tuning of specific frequencies, ensuring tight compliance with the curve. Networked architecture also offers functions not previously possible, such as on-demand paging, 24-hour monitoring, and programmable in-room controls.

Niklas Moeller is Vice President of K.R. Moeller Associates Ltd., manufacturer of the LogiSon Acoustic Network sound masking system (www.logison.com). He also writes an acoustics blog at soundmaskingblog.com.