Page 14 - Fall2020

SPEECH PRIVACY
levels (signal-to-noise ratio) by frequency are seen and illustrate which parts of speech are significantly masked and which parts of speech may be heard and understood.
The three key considerations from Figures 1 and 2 are the background noise, architectural sound blocking, and the source voice.
Background Noise
If we were to lower the background noise, the intruding voice would be unmasked and speech privacy would be compromised. If we raised the background noise, then the intruding speech would be masked even more.
Architecture
Changing the architecture affects the intruding voice. Less robust wall and ceiling choices will attenuate the source voice less, resulting in unmasking of the intruding voice (Figure 2, green line goes up). More robust wall and ceiling choices will better attenuate the source voice so that the intruding voice will be better masked (Figure 2, green line goes down).
Source Voice
The source talker’s effort is a design condition, not a design choice, and will depend on many demographics, but also on the situation. We must consider the use of the space and the experiences within the space. When in a library, many voices may be at a casual or soft effort (lower sound level), but a counseling space may expe- rience emotionally charged and louder conversations (higher sound levels). This, along with speech privacy expectations, dictates the architectural design choices.
If the anticipated source voice is casual and the speech privacy expectation is simply to minimize distraction, then perhaps a furniture partition such as an open office cubical design is sufficient. In a medical office, the vocal effort can be expected to be more conversational, mean- ing a higher effort than a casual voice. Also, the speech privacy expectations are increased due to the sharing of personal, private, and potentially embarrassing infor- mation. This requires completely different architectural solutions. Rooms must now be fully enclosed as in Figure
1. The wall, ceilings, and door design must sufficiently contain the speech within the room so that speech cannot be understood by listeners in adjacent rooms. Voices may be heard, but speech may not be understood.
Designing for Speech Privacy
By considering the expectations and fundamentals of speech privacy, we can put them together with a knowl- edge of privacy architecture and make good design choices. The following are some examples for achieving good speech privacy design in various situations.
Open-Plan Office Spaces
Previously, we touched on open-plan office spaces. These are general larger open spaces with multiple occupant work stations. Because these are shared spaces, it would be unreasonable to expect confidential speech privacy. At the same time, productivity, focus, and overall comfort are very important. Therefore, freedom from speech dis- traction is the expectation. Generally, in such situations, vocal effort is more casual (quieter) but can occasionally increase to normal conversational levels. There can be just a few occupants or many occupants, so the collection of voices and activity can contribute to overall “chatter.”
In open-plan office spaces, good speech privacy design will minimize the radius of distraction. This means that speech will be heard at adjacent workstations, but will an occupant in more distant workstations be distracted by a conversation? If the work requires a higher degree of focus, then furniture partitions at least five feet high will help block sound between workstations. If the occupants need continuous interaction with coworkers, then a partition may be lower or not necessary at all. This will enhance interactive communication but will also increase distrac- tion, which negatively impacts worker productivity.
Architectural acoustics practitioners teach architects the “ABCs of good acoustic design”: Absorb sound in the space, Block sound between spaces, and Cover unwanted sound with the appropriate background noise. The appropriate background noise is always essential for speech privacy, and levels can be elevated in open plan space to reduce speech distraction.
Over the past 20 to 30 years, the architectural trend has been to lower or eliminate partitions between work- stations. This trend was primarily driven by the visual design and occupant density. It will be interesting to see if this trend reverses due to recent health concerns. Future partitions may be transparent elements, such as glass or Plexiglas-type materials, to maintain the visual “open- ness” while maintain social distancing practices.
14 Acoustics Today • Fall 2020