July/August - 39

COMMUNICATION TECHNOLOGY
at the edges than a flat audio decibel (dB) measurement.
According to NFPA 72, " public mode signaling " is required
to provide and maintain a sound pressure level of 15 decibels
(dBA) above ambient sound levels. The designer should
design for and then measure the installation for proper SPLs.
Every time the distance from the loudspeaker is doubled,
the sound pressure drops by as much as 6 dB, so the designer
must plan for this and install the loudspeakers accordingly.
An important term to understand when designing for
intelligibility is an Acoustically Distinguishable Space
(ADS). NFPA 72 defines an ADS as an emergency communications
system zone, subdivision, physically defined
space or section of a room that can be distinguished from
other spaces due to different acoustic, environmental or
use characteristics such as ambient noise floor. All parts of
a building intended to have occupant notification are subdivided
in ADS. If a room has different acoustic properties
in different areas, the areas become multiple ADS. Each
ADS must be identified as either requiring intelligibility
or not requiring intelligibility.
NFPA 72 states that intelligibility is acceptable if at least
90 percent of the measurement locations within each ADS
have a measured STI of not less than 0.45 and an average
STI of not less than 0.5 STI. For native speakers, 0.5 STI
equates to roughly 58% of syllables being understood, 83%
of words understood and 93% of sentences understood.
Audio Improvements at LAX
The $1.6 billion West Gates addition at Los Angeles
International Airport (LAX) features 15 aircraft gates and
an interior organized into a series of " neighborhoods, " each
including multiple aircraft gates, a restroom core and a
wide selection of various retail and concession spaces. The
terminal expansion includes characteristic high ceilings,
reflective glass walls, hard reflective floors and ambient
noise expected from a major transportation hub.
The audio portion of the 750,000-square-foot concourse
construction was critical to LAX as crisp and intelligible
sound helps the airport's millions of annual travelers stay
on the move and up to date with important announcements
and communications. Thus, the loudspeakers had to
provide precise beam control and high speech intelligibility
while offering a discrete footprint to fit the architectural
requirements and constraints.
The airport deployed ICONYX Gen5 arrays from
Renkus-Heinz throughout the terminal to meet their
acoustic needs. Designed explicitly for terminal-wide passenger
announcements and gate announcements, the system
covers all common areas within the terminal, including
all gate seating areas, restrooms, retail and restaurants in
the concourse. This digitally steerable capability produces
crisp and intelligible audio, ensuring everyone hears
announcements clearly.
Clarity Amongst the (Controlled) Chaos
Every listener deserves the clearest sound possible, and
intelligibility is especially critical in transportation hubs.
Designing for intelligibility can be complex since many
factors, such as ambient noise, reverberation, distortion, frequency
response and physical room characteristics, can affect
how much of the message is understood. Designers significantly
impact speech intelligibility through their choice
of equipment, the number, distribution and placement of
loudspeakers, and the power at which those loudspeakers
are driven. When designing AV systems for transportation
hubs, consulting an acoustician or acoustical engineer and
utilizing acoustic modeling software are recommended
to ensure adequate coverage, audibility and intelligibility.
Using loudspeakers with high directivity - such as digitally
steerable arrays - provides you granular control over where
the audio is distributed, decreasing audio fatigue in the
traveler and even reducing travel-related stress. 
ABOUT THE AUTHOR
GARRISON PARKIN
Garrison Parkin is the Western Regional Sales Manager
for Renkus-Heinz.
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