In objective terms, speech privacy is determined by how loud overheard speech is compared to the background sound. Privacy can be increased by reducing the sound level of the overheard speech via sound absorptive room finishes and/or noise reduction from partial or full height partitions.
Privacy also can be increased by adding steady levels of background sound through electronic sound masking. Comfortable limits for sound masking levels are 48 dBA for open-plan areas and 42 to 45 dBA for closed rooms.
The 2010 FGI Guidelines provide objective requirements in terms of “normal” and “confidential” privacy. Normal levels occur when speech is audible, though some effort is required to understand it. Confidential levels occur when speech is audible, but not intelligible.
The 2010 FGI Guidelines have Privacy Index (PI) requirements of 85% or greater for normal privacy and 95% or greater for confidential privacy in closed rooms. The guidelines also call for a PI of 80% or greater for normal levels in open-plan spaces.
Assuming a background sound of 48 dBA and a normal speech level, a listener would need to be at least 23 feet away to achieve normal speech privacy with no barriers. This means that it is important to have barriers that block line-of-sight between talker and listener if the distance is shorter.
In enclosed rooms, the sound transmission class of the partitions and the level of background sound need to be considered.