How often does a sound masking system’s performance need to be measured to ensure it is operating at the target masking volume?
The measurements a vendor or acoustician takes after a sound masking system is installed is an essential part of the commissioning process. A facility manager needs to ensure the volume and spectrum required for speech privacy, noise control and comfort are actually being provided.
A good guideline is to require a test in each 1,000-square-foot open area and every closed room, and that the vendor adjust the masking within each area as needs dictate. Some systems can adjust for smaller areas but this is an acceptable baseline.
Masking volume is typically set between 40 and 48 decibels. The results should be consistent within an overall range of one to 1.5 decibels or less. Frequency should also be measured. There’s a general curve the acoustical community considers effective and comfortable, which is defined in third-octave bands. Plus or minus two decibels variation in each frequency band is a reasonable expectation.
In the weeks following the initial tuning and measurement process, there may be areas that a facility manger would like adjusted based on occupant feedback. It’s not advisable for facility managers to make these adjustments themselves, particularly to frequency. Special training and equipment is required to ensure these changes are properly made, measured and documented.
Though older analog masking systems needed to be checked periodically, the output of modern digital systems is consistent over time. In other words, the masking system itself won’t be subject to variation. However, it’s advisable to measure performance and tweak the system’s settings when:
- Changes are made to physical characteristics of the space. The furnishings, partitions, ceiling and flooring, among other factors, impact the masking sound, regardless of how the loudspeakers are installed (for example, downward facing, cut through the ceiling or upward facing, in the plenum).
- Changes are made to occupancy. For example, relocating call centre or human resource functions to an area formerly occupied by accounting staff will very likely affect masking needs.
The likelihood that these types of changes will occur during a system’s 10 to 20-year life span is almost certain. Therefore, a facility manager can’t simply take a ‘set it and forget it’ approach when it comes to controlling the acoustics of a space. By the same token, a facility manager should also be wary of claims that masking systems don’t need to be adjusted after they’re first installed.