Chapter 3: General Design Guidelines
independent circuit breakers and a dedicated grounding system. Printers
should not be connected to the dedicated computer power supply because of
their uneven power draws. Standard electrical outlets are sufficient for
Two factors--speech intelligibility and privacy--determine the acoustical performance
of spaces in a courthouse. Speech intelligibility is a measure of the ability of a listener
in the room to understand what is being said. Privacy is the measure of limiting
speech intelligibility to the intended listener. The acoustic performance of a space can
be specified by a synthesis of acoustical parameters, which can be predicted and
measured during design.
Two primary determinants of acoustic performance with respect to speech
intelligibility are the level of background noise and reverberation.
Background, or ambient, noise is produced by several predictable sources. Most
common is the movement of air for heating or cooling the room. Sources of
background noise include diffusers, fans, and the activity of people inside and outside
the courtroom. Noise criteria describes the desired level of background noise.
The second determinant is reverberation. Reverberation is measured in terms of the
time it takes for sound to subside in a room. This measure is known as the
"reverberation time" and is expressed in seconds. Reverberation times that are too long
can create delays in reflected sound (echoes), which compromise speech intelligibility.
Therefore, wall construction and finishes must be carefully selected to promote proper
Intelligibility is determined by the combined effect of background noise, reverberation,
and other contributing factors. Several measures have been developed in pursuit of a
single number to quantitatively represent speech intelligibility. Primary among these
are the Articulation Index (AI) and the Rapid Analysis Speech Transmission Index
(RASTI). Both AI and RASTI are based on measures of a speech-to-noise ratio and