Noise Isolation-- the amount of noise transmitted
Speech Privacy-- the amount of speech that can be
through the perimeter boundary elements of a space.
understood in a space adjacent to the location where a
Sound transmission class (STC) quantifies the sound
conversation is occurring. Articulation Index (AI) is a
insulating performance of building elements such as
measure of the intelligibility of speech, which is related to
walls, windows, and doors when tested in a laboratory in
the level of the speech relative to the level of the
accordance with ASTM E90. Noise Isolation Class (NIC)
background noise at a particular location. When tested in
quantifies the field-tested sound isolation between two
open plan offices in accordance with ASTM E1130, AI
enclosed spaces separated by a partition when tested in
takes into account the noise reduction of partitions
accordance with ASTM E336. NIC accounts for both
between spaces, the absorption in spaces, the distance
the sound insulating performance of the partition, and
between source (talker) and receiver (listener), the level
unintentional paths ("flanking paths") between the
of the background noise, and typical voice levels. AI is a
spaces (e.g. wall/ceiling connections, partition
single number rating between 0 and 1; lower AI values
penetrations, etc.). The numerical value of NIC is usually
mean fewer words can be understood, indicating
less than that of the STC for the separating partition.
increased privacy. An AI value of .05 indicates less than
NIC should only tested in fully furnished spaces. Ceiling
8% of speech in an adjacent space can be understood and
is considered the upper threshold of "confidential" speech
performance of a ceiling assembly spanning across rooms
privacy. An AI of .15 means indicates that, with
that share a common plenum when tested in accordance
concentrated effort, nearly two-thirds of speech in an
with ASTM E1414. Field Impact Insulation Class (FIIC)
adjacent space can be understood. Recent research
quantifies the field-tested impact sound insulating
indicates that above this level, intruding conversation
properties of a floor/ceiling assembly when tested in
may become distracting. An AI of .20 is considered the
accordance with ASTM E1007. Greater STC, NIC, CAC
upper threshold for "normal" speech privacy.
or FIIC values represent better performance.
Reverberation Time-- the time required for sound to
are determined by the use of a space and the require-
decay 60 decibels in the 500 Hz band in an enclosed
ments of its occupants. It is the responsibility of the
space. Reverberation time becomes longer as the sound
design team to meet the following minimum standards
absorption is reduced and/or the room volume increases.
governing the acoustical performance of various space
usage categories.
Sound Absorption-- the amount of sound absorbed by a
surface finish. Sound absorption average (SAA) quantifies
Environmental Noise. The impact of site noise on a
the efficiency of a material in absorbing sound energy
building's interior spaces shall be mitigated under any of
when tested in accordance with ASTM C423 (SAA
the following conditions:
replaces the earlier noise reduction coefficient or NRC).
Building is located within an airport noise contour of DNL
SAA/NRC is a single number rating between 0 and 1.
60 or greater
Greater SAA/NRC values represent a more effective
Building is located within 500 feet of a freeway or railroad
sound absorber. An excessive amount of reflected sound
right-of-way
(reverberation) tends to degrade speech communication.
DNL at the building's property line exceeds 70 dB
77
ARCHITECTURAL
AND
INTERIOR
DESIGN
3.4
Special Design Considerations
Revised March 2005 PBS-P100
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