Designing for acoustic privacy
Of course, the louder a person speaks, the more likely he or she is to be heard. Building occupants should always try to be mindful of their voice level, but proper etiquette is only effective to a point. The remainder of the acoustical burden has to be borne by the design using a three-tiered approach called the ‘ABC Rule,’ which stands for absorb, block, and cover. Acoustic privacy is achieved by using a well-designed combination of these tactics. (The brief outline in this article touches on the interior fit-out and furnishings, not the shell of a building.)
Absorb
The ‘A’ in ‘ABC’ stands for adding absorption. As speech sounds hit various surfaces within a facility, they are reflected back into the space. If those surfaces comprise hard materials such as concrete, glass, and metal, the reflected sound energy remains high and the overall volumes will rise.
A high percentage of hard surfaces also increases reverberation (i.e. echo) within the space, making it uncomfortable. Additionally, it can lower intelligibility due to the presence of more persistent sounds in the space, often referred to as the ‘cafeteria effect.’However, it can also increase intelligibility—particularly in situations where there are not a lot of competing voices—because voice travels a longer distance and, hence, conversations can be heard from further away.
To control this type of transmission, absorptive materials must be applied to the ceiling, walls, and workstation partitions. As the ceiling is usually the largest unimpeded surface within a facility, organizations should invest in the best acoustic tiles or panels they can afford and ensure consistent coverage throughout their space.
Block
The ‘B’ stands for blocking speech transmission using walls, windows, doors, and other physical structures. This method is most obviously used in the construction of enclosed rooms, but it is also extremely useful within the open plan. If there are no barriers between occupants in these spaces, speech travels more easily and the ability to see (and be seen) further reduces privacy due to the natural capacity for lip-reading. Again, though some might argue privacy is not expected within an open plan, understandable speech disrupts occupants’ concentration. For this reason, workstation partitions should be no lower than seated head height—that is, 1524 to 1651 mm (60 to 65 in.). Even the direction in which people face will often have an effect on their voices’ volume within the neighbouring workspace. Therefore, occupants should be seated facing away from each other on either side of partitions.
Today, there are numerous pressures to reduce the height of workstations or eliminate them altogether. This trend has had a dramatic impact on the acoustical performance of open plans because though other treatments can reduce overall volume levels and deal with noises generated from farther away, they have no effect over very short distances. When barriers are eliminated, local noise sources remain highly intelligible and disruptive.
Cover
‘C’ stands for covering, which can involve installing a sound masking system. This technology consists of a series of electronic components and loudspeakers typically installed above the suspended ceiling, which distribute a comfortable background sound throughout the facility. Though most people compare the output of a well-designed and professionally tuned masking system to that of softly blowing air, it has been specifically engineered to cover the range of frequencies in human speech. This sound also covers up incidental noises arising from general workplace activities or minimizes their disruptive impact on occupants by reducing the change between baseline and peak volume levels within the space.
