sound masking

The evolution of sound masking technology

How the architecture of these systems influences speech privacy and other performance goals
Friday, July 15, 2016
By Niklas Moeller

Most facilities feature an insufficient level of ambient sound, leaving employees trying to work in a ‘pin-drop’ environment in which they can easily hear conversations and noises.

When using a sound masking system to address this issue, it is vital to ensure that the engineered sound it distributes is not only effective, but as unobtrusive as possible. Unlike ‘white noise’ or ‘pink noise’— terms often, but mistakenly, used in this context — sound masking follows a non-linear curve specifically designed to balance acoustic control and occupant comfort. A successful implementation involves achieving both goals, in equal measure.

No sound masking system can accomplish these objectives ‘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 elements across the facility’s interior. In order to meet the specified curve, an acoustician or trained technician measures the sound at ear height, examines the results, and adjusts the system’s volume and frequency settings accordingly. This process can be time-consuming, but it is essential to ensure the sound provides the intended effects and that they are enjoyed equally by all occupants.

However, it is impossible to achieve perfection in every tuning location. Consequently, a masking specification will also include a ‘tolerance’ indicating how much the sound is allowed to deviate from the target curve across the treated space. Because variations can affect performance and comfort, it is vital to keep this value to a minimum — a fact emphasized by how the architecture or ‘electronic design’ used by this technology has evolved over the decades.

Centralized architecture

Centralized architecture originated in the 1960s. In this configuration, the equipment used for sound generation, volume and frequency control is located in a closet or room and connected to a large number of loudspeakers, forming a zone.

The facility is divided into basic categories such as open plan, closed room, corridor and reception, and a zone is created for each type. Each zone is then set to a ‘best average’ level; however, the sound fluctuates as it interacts with the workplace’s design. If the volume must be increased due to a performance deficiency in one area, that change is applied to the entire zone, making it too loud in others, or vice versa. Most designs offer volume control at each loudspeaker, but it is usually limited to a few large steps. Furthermore, each zone only offers global control over frequency.

Because the sound cannot be finely adjusted in local areas, centralized system specifications allow a wide tolerance, even as much as plus or minus two A-weighted decibels (dBA), giving an overall range of four dBA across the space. One can usually expect a 10-per-cent reduction in performance for each decibel below the target masking volume. In other words, such a broad tolerance can lead to a 40-per-cent performance loss in unpredictable locations across the facility.

Decentralized architecture

In the mid-1970s, engineers developed decentralized architecture in order to address the tuning obstacles posed by large zones.

In this configuration, the electronics used for sound generation, volume and contour control are integrated into ‘master’ loudspeakers. 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 square feet or 30 to 62 square metres). Each zone also offers fine volume control, allowing local variations to be addressed and, hence, a more consistent masking level to be achieved across the facility.

However, frequency adjustment is still limited. Furthermore, the acoustician or technician has to make changes directly at each master using a screwdriver or an infrared remote control. It is advisable to modify a sound masking system’s settings when changes are made to the physical characteristics of a space (e.g. furnishings, partitions, ceiling, flooring) or to occupancy (e.g. relocating a call centre into an area formerly occupied by accounting staff). It is almost certain that these types of changes will occur during a system’s lifespan. Therefore, engineers needed to develop a more practical way of adjusting the sound.

Networked architecture

The first networked sound masking system was introduced more than a decade ago. This technology leverages the benefits of decentralized electronics, but also networks the system’s components together throughout the facility or across an entire campus. Components are addressable in order to provide full control over all settings from a control panel and/or software. Adjustments can easily be made as needed, maintaining peak performance over the life of the system.

When designed with small zones of one to three loudspeakers offering fine volume (i.e. 0.5 dBA) and frequency (i.e. one-third octave) control, networked architecture can provide consistency in the overall masking volume not exceeding plus or minus 0.5 dBA (i.e. one dBA overall), yielding much better results than previous architectures. Some networked systems are tuned using a computer, which rapidly and accurately adjusts the masking output to match the specified curve.

Zoning for functions such as paging and occupant control are independent from each other and handled digitally rather than by hardwiring, allowing changes to be made without altering the system’s physical design. Furthermore, networked architecture allows integrators to offer functions not possible with earlier configurations, including on-demand paging, 24-hour monitoring, email notification, programmable in-room controls, and integration with other building control systems.

Hybrid archiecture

Vendors have also experimented with combining architectures — for example, by providing individual zones for closed rooms and large zones across open plans. However, as noted above, centralized architecture is unable to adjust for acoustical variations across the floor plate, which can be considerable, even within an open plan.

In the end, variations can significantly impact speech privacy, noise control and occupant comfort; therefore, it is vital for the masking sound to be delivered within the highest degree of precision and consistency possible. Fortunately, this goal can be cost-effectively achieved with modern sound-masking architecture. While being able to properly categorize a technology as centralized, decentralized or networked will not tell one everything it can or cannot do, its architecture provides the foundation for its performance and, hence, it is the best place to start.

Niklas Moeller is the vice-president of K.R. Moeller Associates Ltd., manufacturer of the LogiSon Acoustic Network sound masking system. He also writes an acoustics blog.

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