ARCHIVED - Minimizing speech security risks for meeting rooms
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December 23, 2009— Ottawa, Ontario
Dr. John Bradley makes no apologies for the hours he spends trying to hear conversations through closed doors.
As a world leader in room acoustics, the NRC researcher has spent years listening to and measuring speech transmitted through real and simulated walls and doors — all in an effort to help architects and acoustical consultants design spaces that will ensure sensitive conversations will not be overheard.
"We hear a lot of complaints about the lack of privacy in offices and meeting rooms that are used for private discussions," says Dr. Bradley. "With strengthening privacy legislation and heightened security concerns, it is no longer acceptable that conversations occurring ‘behind closed doors' can even accidentally be overheard in adjoining spaces." Indeed, government departments now require new design and assessment procedures for the speech security of meeting rooms.
Although the concept of speech privacy has been around for more than 50 years, he says until recently, very little has been done to develop standard procedures and acceptable criteria that will ensure satisfactory privacy.
Rating speech privacy
That is changing. Dr. Bradley's team, in partnership with Public Works and Government Services Canada (PWGSC) and the Royal Canadian Mounted Police, has developed a procedure for rating the speech privacy of enclosed rooms.
The new "speech privacy class" (SPC) measure can rate the level of privacy or security of a room on a numeric scale from 70 (speech is frequently intelligible, sound is audible) to 90+ (speech unintelligible, sound is rarely audible), or by categories ranging from minimal speech privacy to very high speech security. The degree of protection depends on two main building-related factors: the sound insulation between the interior of the room and the position of an eavesdropper outside the room, along with the background noise level at the listener position.
To develop the SPC system, Dr. Bradley's team asked volunteers to listen to test sentences that were modified to simulate transmission through various walls. The volunteers were instructed to indicate whether any speech sounds were audible and, if they were audible, to repeat as many words as possible of each test sentence.
By measuring the sounds at the listener position, and comparing the measured values with the volunteers' responses, the NRC team created a new signal-to-noise ratio measure that can accurately predict the expected level of the audibility or intelligibility of the transmitted speech.
Since speech levels in meetings can vary from moment to moment, the risk of speech privacy problems occurring is related to the likelihood of higher speech levels occurring. For example, in a very "speech secure" room, speech may be transmitted through the room's walls less than once in a 24 hour period.
"You can classify a room in the same way you classify the information discussed in it," says Dr. Bradley. "Once the room has a rating, you can determine a suitable wall construction that provides adequate sound attenuation to match the desired privacy rating. Of course, an easy way to ensure the security of a conversation is to ensure there is a lot of background noise outside the room. But that is rarely practical as it would likely prove distracting for people in nearby offices."
From an architectural design point of view, building walls with a high level of sound attenuation is relatively easy, he adds. It is much harder to provide similarly effective doors. Pipes and ventilation ducts can also diminish the effectiveness of the sound insulation provided by a room.
So far, the NRC team's SPC procedures have been incorporated into an international standard, which is expected to have broad application across all building types. The procedures are also being used by acoustical consultants working on the renovations of the West Block of Parliament Hill.
He says the next step is to get officials at various government departments to identify their speech privacy needs in order to determine how to assign SPC requirements to various conditions. This may ultimately help ensure the system's wider adoption to meet growing privacy concerns.
Dr. Bradley stresses that the speech privacy scale is designed to rate the privacy provided by the architectural features of the building and not more overt forms of eavesdropping involving contact with a wall or the use of electronic monitoring devices.
- NRC Institute for Research in Construction
- Building a better office cubicle
- Procedures for designing and assessing the speech security of meeting rooms
- Measures for assessing architectural speech security (privacy) of closed offices and meeting rooms (in English)
- Spatial and temporal effects of room acoustics on the speech privacy of meeting rooms (in English)
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National Research Council of Canada
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