U.S. Courts Design Guide
reverberation time in several bands of sound frequencies. Intelligibility is expressed
throughout the Guide as RASTI criteria.
Spaces in a courthouse are designed to provide one of four levels of acoustical
privacy: inaudible, confidential, normal, and minimal. Inaudible privacy requires that
no sound whatsoever travels between space. Confidential privacy means that sound
can be detected but it is impossible to understand what is being said. For a normal
level of privacy, eavesdropping is required to understand what is being said in
adjacent areas. A minimal level of privacy provides only partial control of distracting
The level of privacy is determined by the loudness of speech, transmitting
characteristics of the partition between spaces, and the background noise in the
originating and receiving spaces. The acoustical properties of a partition can be
specified by its Sound Transmission Coefficient (STC). Privacy criteria in the Guide
are expressed as Noise Isolation Classification (NIC), which represents the level of
privacy that results from the combined determinant. The STC of a given design can be
generally predicted; however, the NIC can only be measured after a space is
constructed and occupied. To assure that the desired privacy level is achieved, a
sound-masking system can be installed outside sensitive spaces.
The following is a list of NIC ratings for privacy levels found in a courthouse:
The following factors affecting privacy must be taken into consideration during design:
The sound level inside the room is a major factor. It determines the noise
reduction that an intervening wall must provide to assure that conversations
are not heard outside the space.
Less-critical structures such as storage areas can be placed between the sound
source and the receiving room. These structures are normally storage areas,
less-critical offices, or other semi-public spaces.
Because traffic circulation adjacent to a space affects the type of construction
necessary to ensure privacy, in certain cases, a sensitive space should be
located away from traffic circulation.