Architectural Evolution

The importance of spatial uniformity in the masking sound (i.e. achieving tight tuning tolerances throughout the space) is also emphasized by the evolution of sound masking architecture. Since the technology was first introduced in the 1960s, numerous advancements have been made in order to make tuning a more precise and efficient exercise.

Centralized Sound Masking

The earliest sound masking systems used a centralized architecture. The name derives from the fact that the electronic components used to generate the masking sound, as well as to provide volume and frequency control and amplification, are all located within an equipment room or closet. The settings established at this central point are broadcast over a large number of loudspeakers—sometimes as many as hundreds. While most offer limited analog volume control at each loudspeaker (usually four to five settings, in 3 dBA steps), their centralized design means that large areas of the facility are nonetheless served by a single set of output settings with little or no option for local adjustment.

Image courtesy of K.R. Moeller Associates Ltd.

A centralized masking architecture consists of a centrally located rack of electronic equipment that is used for sound generation, volume, and frequency adjustment. This equipment is connected to a large number of loudspeakers—as few as eight, or as many as hundreds—forming a single adjustment zone.

Because the technician cannot make precise volume changes in specific areas, he or she has to set each large zone (i.e. individually controllable groups of loudspeakers) to a level that is best ‘on average.’ Due to variations in the acoustic conditions across the space and the impact of interior elements, the masking sound is too low in some areas and too high in others. If the technician raises the volume to address a performance deficiency in one area, the sheer size of the zone means the volume simultaneously increases in others, affecting occupant comfort. If the technician lowers it to boost comfort, speech privacy and noise control is sacrificed. This pattern repeats at unpredictable points across the space, which is why central system specifications typically allow large variations in overall masking volume. Tolerance is typically 4 to 6 decibels (i.e. ±2 to 3 dBA). Furthermore, centralized architecture only provides a global frequency control for each large zone.

Centralized architectures are also prone to a phenomenon called phasing, or noticeable variations in the masking level. In order to try to avoid this problem, technicians employ a dual-channel, interlaced design, ensuring that adjacent loudspeakers do not emit the same masking signal; however, it requires two sets of centrally-located electronic equipment per zone, raising costs.

Decentralized sound masking

Decentralized architecture emerged in the mid-1970s in order to address a major deficiency in the ability to tune centralized systems: large zone size. Rather than locating sound generation, volume, and frequency control in a central location, the electronics required for these functions are integrated into ‘master’ loudspeakers, which are distributed throughout the facility—hence the ‘decentralized’ name.

Image courtesy of K.R. Moeller Associates Ltd.

A decentralized masking architecture uses ‘master’ loudspeakers to house the electronics needed for sound generation, volume, and contour control. Adjustment zones are one to three loudspeakers in size. Local changes are made using a screwdriver or remote control.

Each ‘master’ is connected to up to two ‘satellite’ loudspeakers, which repeat their settings. Therefore, a decentralized system’s zones are only one to three loudspeakers in size (i.e. 225 to 675 ft2 [30 to 62 m2]). This distributed design inherently controls phasing. In addition, because each small zone offers fine volume control, local variations can addressed, allowing more consistent and, hence, effective masking levels to be achieved across a facility. However, there are still limits to the adjustments that can be made with respect to frequency, which impacts performance.

Furthermore, a technician must make changes directly at each ‘master’ loudspeaker, using either a screwdriver (i.e. with analog controls) or an infrared remote (i.e. with digital controls), making future adjustments challenging. It is advisable to measure performance and modify a sound masking system’s settings when changes are made to the physical characteristics of the space (e.g. furnishings, partitions, ceiling, flooring) or to occupancy (e.g. relocating a call center or human resource functions into an area formerly occupied by accounting staff). The likelihood that these types of change will occur during a sound masking system’s 10- to 20-year lifespan is almost certain; therefore, one cannot take a ‘set-it-and-forget-it’ approach. Engineers needed to develop a more practical way of adjusting the masking sound.

Networked sound masking

The first networked sound masking system was introduced just more than a decade ago. This technology leverages the benefits of decentralized electronics, but networks the system’s components together throughout the facility—or across multiple facilities—in order to provide centralized control of all functions via a control panel and/or software. Changes can also quickly be made following renovations, moving furniture or personnel, maintaining masking performance within the space without disrupting operations.

Image courtesy of K.R. Moeller Associates Ltd.

A networked masking architecture uses ‘hubs’ to house the electronics required for sound generation, volume, and frequency control. Adjustment zones are one to three loudspeakers in size. All local and global changes, including those to zoning, are made from a central location, such as a small panel or software application.

When designed with small zones of one to three loudspeakers offering fine volume (i.e. 0.5 dBA) and frequency (i.e. 1/3 octave) control, networked architecture can provide consistency in the overall masking volume not exceeding ±0.5 dBA, as well as highly consistent masking spectrums, yielding much better tuning results than possible with previous architectures. Some networked sound masking systems can also be automatically tuned using a computer, which first measures the sound and then rapidly adjusts the masking output to match the specified curve.

Today, there are a number of different product offerings within the centralized, decentralized, and networked categories. Some vendors have also utilized a hybrid design, implementing a decentralized architecture in closed rooms (e.g. private offices) and a centralized architecture in the open plan. However, it should be noted that the centralized architecture presents significant tuning challenges in the type of area where occupants are likely to rely on masking the most for speech privacy and noise control.