AST Digital Magazine June 2017 Digital-June | Page 5

Volume 13
It is affected by the quality of the original mes-
sage transmitted, the level of background noise,
reverberation and, for messages transmitted
over an MNS, the properties of the communica-
tion system.
June 2017 Edition
els at various sites. With this large database of
empirical data and in-house expertise in the field
of acoustics, ATI Systems developed an in-depth
acoustic model for optimal MNS design.
The original message must be spoken clearly
and more slowly than the typical person to per-
son speech.
Background noise can mask an emergency mes-
sage in what is known as the signal to noise ratio,
and reverberation can blur the speech over time
by lengthening vowels and shortening pauses.
All of these factors must be considered in MNS
design to create the most effective Giant Voice or
PA system.
Selecting Your Mass Notification System
The size and shape of the outdoor space or in-
door area are also very important considerations
in MNS design.
When designing a system for maximum intelligi-
bility in an outdoor area, conditions to consider
include topography, atmospheric conditions, and
ground cover.
For indoor systems, reverberation is a more im-
portant factor. In both cases, background noise
levels and the other factors listed above must
also be considered.
ATI Systems’ acoustic computer model uti-
lizes state-of-the-art methodology to predict
MNS sound coverage.
The computer model uses a 15-decibel differen-
tial above ambient noise for the entire acoustic
coverage area, and takes into consideration fac-
tors such as:
• Hemispherical wave divergence
• Atmospheric absorption of sound, and the
• Local situation of the MNS, be it outdoor or
indoor
ATI Systems conducts a comprehensive acous-
tic analysis to evaluate the voice coverage of
the facility or outdoor area, develops the recom-
mended layout of speakers or other alerting de-
vices, and provides the resulting acoustic cover-
age mapping.
Acoustic Technology Inc. (ATI Systems), a com-
petitor in the 2017 ‘ASTORS’ Homeland Secu-
rity Awards program, has been considering the
questions of MNS effectiveness and background
noise for over 30 years.
ATI Systems started out as an acoustic consulting
firm, advising industry and government groups
about emergency alerting, and helped in devel-
oping some of the early standards in this field.
As part of this work, ATI Systems measured nu-
merous siren signals and background noise lev-
An example of an ATI outdoor acoustic coverage map
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