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iv
Influences on Intelligibility............................................................................................ 3-2
Introduction .............................................................................................................. 3-2
Background Noise ................................................................................................... 3-3
Reverberation .......................................................................................................... 3-4
Distortion.................................................................................................................. 3-5
Microphone Technique ............................................................................................ 3-5
Measures of Intelligibility ............................................................................................. 3-6
Introduction .............................................................................................................. 3-6
The Common Intelligibility Scale (CIS) .................................................................... 3-6
The STI Method ....................................................................................................... 3-7
STIpa ....................................................................................................................... 3-7
STITEL..................................................................................................................... 3-7
RASTI ...................................................................................................................... 3-7
Percent (%) ALcons................................................................................................. 3-7
Phonetically Balanced Word Scores ....................................................................... 3-7
Practical Measurement of Intelligibility ........................................................................ 3-8
Introduction .............................................................................................................. 3-8
Tools for Predicting Intelligibility .................................................................................. 3-9
Introduction .............................................................................................................. 3-9
Acoustical Modeling Software ................................................................................. 3-9
Chapter 4 Emergency Voice/Alarm Communications Systems 4-1
Introduction .............................................................................................................. 4-1
In this Chapter ......................................................................................................... 4-1
A Typical Emergency Voice/Alarm Communications System ..................................... 4-2
Parts of an Emergency Voice/Alarm Communications System .................................. 4-3
Command Center .................................................................................................... 4-3
Audio Riser .............................................................................................................. 4-3
Transponder ............................................................................................................ 4-3
Speaker Circuits ...................................................................................................... 4-4
Chapter 5 Regulatory Issues 5-1
Introduction .............................................................................................................. 5-1
In this Chapter ......................................................................................................... 5-1
Audibility ......................................................................................................................5-2
Tones and SPL ........................................................................................................ 5-2
High Background Noise........................................................................................... 5-3
Large Areas ............................................................................................................. 5-3
Intelligibility .................................................................................................................. 5-4
Intelligibility .............................................................................................................. 5-4
Intelligibility Certification .......................................................................................... 5-5
Chapter 6 Speaker System Design Method 6-1
Introduction .............................................................................................................. 6-1
In this Chapter ......................................................................................................... 6-1
Speaker Design Method .............................................................................................. 6-2
Introduction .............................................................................................................. 6-2