Preparing a Performance-Based Specification

Preparing or even evaluating a sound-masking specification can be challenging, but the payoff is worth the effort. These systems typically have a long lifespan. When properly designed, they help to keep acoustics under control even as densities swell and, if included in a project’s planning stages, they also increase flexibility, typically allowing an organization to remain in its facility for a longer period. In other words, the user can end up living with the system for quite some time.

Currently, sound-masking systems are often specified according to the aforementioned types—centralized, decentralized, or networked—limiting the number of vendors that can bid on a given project. Bidding opportunities are further restricted when the specification incorporates proprietary elements such as the dimensions of components, types of inputs/outputs, and other minor details. At the other end of this spectrum are specifications that merely state “provide a sound-masking system.” When compared to the manner in which most other building systems such a HVAC or fire alarms are specified, the contrast is striking.

The single most important factor within a sound-masking specification is to place an upper limit on control-zone size. Control zones are groups of loudspeakers for which the technician can establish individual volume and frequency settings. From a performance perspective, one loudspeaker in each zone is ideal, but it can be an acceptable compromise—and more budget friendly—to have up to three, at least across open plans.

Acoustical conditions and user needs vary between private offices, meeting rooms, corridors, and reception areas, as well as across open plans. Designs that use large adjustment zones (e.g., involving more than a few loudspeakers) require one to make ever-increasing compromises. For example, if the volume needs to be raised to improve masking effectiveness in one area, it might be too loud in another, affecting comfort. If comfort is desired, masking effectiveness may be diminished in some areas. Furthermore, as shown in the graph, the larger the zone, the greater the number of occupants it affects. The numbers ramp up very quickly, from an average of 1.3 people in a single loudspeaker zone to literally hundreds of people and tens of thousands of square feet in a 100 loudspeaker zone.

Zone size also affects the ease with which the technician can make changes in response to (for example, renovations or moving personnel). Large zones require the system’s design to be altered, which usually involves moving loudspeakers and rewiring.

In this case, less truly is more: one to three loudspeakers in each zone (i.e., covering 225–675 square feet) provides a high degree of control and flexibility, enabling technicians to adjust their volume and frequency to achieve a consistently effective and comfortable masking sound.

Even if the specification is well written, the user can end up with a nonconforming sound-masking system unless someone is appointed as a guardian who is responsible for ensuring that bids—and the system ultimately selected—meet the criteria. Requiring drawings as part of the bid-submission process can help because they make it easier to spot design shortcuts. Asking vendors to complete a compliance form that indicates their adherence to each aspect of the specification—and explains any deviations—is also useful.

Because a sound-masking system’s ability to provide the intended effect is directly related to the ability to closely match the target curve throughout the space, the vendor should also provide the client with a detailed tuning report demonstrating that the desired curve is consistently provided throughout the space. If there are any areas where the masking sound is outside tolerance, this document should clearly identify the location and reason (e.g., noise from mechanical equipment or HVAC). In this way, the client can be confident that the sound-masking system’s benefits are enjoyed by all occupants in the facility.