You can’t truly know whether your sound masking system is performing as you want it to until you measure after it’s installed and tuned.
Make sure your vendor or acoustician tests in 1000 ft2 (93 m2) open-plan area and each closed room, and have your vendor adjust the sound masking system within that area as needs dictate.
Note that some providers may outperform this requirement, but it is a good baseline.
To ensure comfort and dependable performance across your space, overall volume should be consistent within a range of 1 dBA (±0.5 dBA) or less. The volume of each third-octave frequency should meet the specified level as closely as possible. You can specify ±2 dB within each band, but note that this is the maximum allowable deviation and should only occur within a few bands, not as a rule.
With these six factors forming the basis of your choice, feel free to add any other requirements you see fit—for example, the appearance of the loudspeakers in an open ceiling, UL 2043 compliance, and so on.
Additional considerations can include: control methods; zoning methods; timer functions; paging and music functions; security features; certifications; installation versatility; scalability; and appearance.