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Measurement of intelligibility can be complicated, and it sometimes includes subjective analysis.
To effectively implement intelligible systems in real buildings requires that a simple, accurate, and
repeatable method of measuring intelligibility must be available. Fortunately, there are instruments
on the market that meet this need. One of these is the STI-CIS meter available from SimplexGrinnell.
The meter uses the STIpa method to provide a fast and easy measurement of total system speech
intelligibility. It measures both intelligibility and audibility, as it also has a built in dB meter.
The meter automatically converts the STIpa measurement to CIS so that demonstrating that a
system meets the requirements of NFPA 72 is easy and intuitive.
A proprietary test tone is played through the system which the analyzer uses to determine
reduction in speech modulation.
Figure 3-5. STI-CIS Intelligibility Measurement System
Practical Measurement of Intelligibility
Introduction
Microphone
AC Ada
p
ter
STIpa
Test Tone CD
AC Ada
p
ter
STI-CIS Analyzer
Talkbox
Volume
Control
Microphone
Holder
CD Player
Speaker