This process is handled by a qualified technician after the ceilings and all furnishings are in place, and with mechanical systems operating at normal daytime levels. Since conversations and activities can prevent accurate measurement, it is done prior to occupation or after hours. Basically, the technician uses a sound level meter to measure the masking sound at ear height. They analyze the results and adjust the system’s volume and equalizer controls accordingly. They repeat this process as often as needed until they meet the curve, within the specified tolerances, at each tuning location.
The purpose of tuning is to ensure the system’s benefits are consistently experienced by all occupants across the facility. Deviations from the curve have a profound impact on masking performance. For instance, even if the curve’s shape is maintained, each decibel drop in overall volume results in a 10 per cent drop in speech privacy. Consistency is also important for comfort—the sound fades into the background and occupants come to consider it a natural part of their space.
So, why is white noise often associated with sound masking? It is because the original masking systems developed in the late 1960s and 70s actually used white noise generators. The problem is while white noise is an effective masker, it is also irritating. Due to the poor quality of the sound, these systems were usually turned down or off soon after installation.
In that sense, when people talk about white (or pink) noise systems, they are inadvertently referring to older masking technologies. These systems typically featured centralized architecture, meaning their electronics were housed in a central location within the facility and the sound output from that equipment was broadcast over zones consisting of dozens or even hundreds of loudspeakers. They offered little to no local control over the masking volume and equalization, so these systems were unable to consistently deliver the specified curve across a facility. Centralized designs typically allow up to four A-weighted decibels (dBA) of variation across a space, causing as much as a 43 per cent drop in privacy.
Modern sound masking systems are capable of producing far more consistent—and, hence, reliable—performance, with overall volume variations of just ±0.5 dBA. They use small zones of one to three loudspeakers and offer precise control over volume and individual one-third octave frequencies within each. Local adjustment of each zone is facilitated by networked control over settings. Clients can be assured of their sound masking system’s performance by asking the acoustician or vendor to provide detailed reporting of tuning results.
To be clear, most people do not think of the technical implications when they say ‘white noise’ or ‘pink noise’ and really mean ‘sound masking.’ However, it is important to differentiate between these terms because the negative associations with white noise persist, despite sound masking technology coming such a long way since those very early days.
For more on sound masking, read this author’s article on acoustic privacy in the June 2015 issue of Construction Canada.
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 at soundmaskingblog.com.