Blog > Sound (Un)Masking: An Overview of Speech Privacy Systems February 25, 2016

Sound (Un)Masking: An Overview of Speech Privacy Systems

In a previous post, I discussed the benefits of a moderate and reasonable level of background sound to improve one’s sense of privacy. In this post, let’s focus a bit more on the specifics of this background sound.

To provide more privacy and less distraction, it is useful for the acoustical conditions to include a background sound that is consistent (not fluctuating over time), uniform (not fluctuating as you move around the space), moderate in level (not too loud and not too quiet) and broadband (sounds like airflow noise; not tonal). Sounds with this character help to establish a neutral acoustical environment that provides its benefits by being in the background and unobtrusive. This type of background sound helps to cover up, or mask, sounds that are less pleasant, intrusive or distracting.

This background sound can be generated by any number of different sources. In one’s home, one might find the sound of a fan, humidifier/dehumidifier, air cleaner, or even a heater/air conditioning are suitable sources. For those who may think this type of sound is merely noise (which is defined as unwanted sound), you might want to consider that this sound is nearly similar to that which is produced by a waterfall, which might provide a more natural and refreshing image. Along the same line, water fountains in outdoor parks can also be used to produce a pleasant sound that may help to mask the noise from the surrounding urban chaos.

In an office space with open workstations, the presence of moderate background sound is important to help one feel more private from their peers (again, the premise of the previous post: we like spaces with a moderate background sound because we can concentrate and focus more effectively). However, in a large office, it would be wastefully inefficient and/or impractical to provide everyone on the staff with a fan, humidifier/dehumidifier, air cleaner or a water feature to generate such background sounds. One might ask, “Well, why not design the HVAC (heating ventilating and air conditioning) to provide this sound?” There are numerous challenges to using HVAC systems for such sound, most importantly that the sound from HVAC systems is rarely uniform throughout a space, or consistent over time, and can be tonal and unpleasant in character. Perhaps the one HVAC source that might be close to this type of background sound is the airflow noise from a diffuser (the grille where the air comes out), but again, this type of sound is typically very localized (helping some people, but not others) and may fluctuate over time. This noise is typically a symptom of poor air distribution, which is not desired from a thermal perspective and generating this airflow sound requires significant extra energy for the fan, which is wasteful. Therefore another source for creating this background sound should be considered.

This leads us to electronic systems, which are referred to as “sound masking” or “speech privacy” systems. You may have also heard of these systems referred to as “white noise” systems, though technically, they are not producing what is characteristically defined as “white” noise (page 175, 12.4.1). With these electronic systems, the spectrum of the sound that they produce is tuned to mask speech, while also remaining a neutral and unobtrusive sound for the occupants.

The main reason for using these electronic systems are that they produce a sound that is consistent over time, uniform spatially, broadband, and easily adjustable in level. They accomplish this using an electronic sound generator (also referred to as the controller), amplifier, wires and loudspeakers (sometimes called emitters). The sound is typically between 42 and 47 dBA to provide a suitable acoustical environment for the background of typical office activities. The quieter sound levels are typically used in private offices sharing common ceiling plans to adjacent spaces, while the higher sound levels are used in open plan work spaces. Note that sound masking is not to be used in conference rooms, meeting rooms, or other spaces where the ability to hear and listen to speech is important.

In the end, these sound masking systems provide occupants with the benefit of hearing less of the sounds that would be distracting and intrusive to concentration. This works well in offices, libraries, lounge, etc. This can also work well in homes for people who live near bus stops or maybe when neighbors make louder noises when one is trying to sleep. The masking sound reduces one’s sensitivity to the intrusive noises that impede and impair the use, comfort or enjoyment of a space.

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