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Chapter 1 Speech Intelligibility Overview 1-1
Introduction .............................................................................................................. 1-1
Chapters of this Publication ..................................................................................... 1-1
In this Chapter ......................................................................................................... 1-1
Importance of Audible and Intelligible Emergency Communications .......................... 1-2
Speech Intelligibility Importance .............................................................................. 1-2
Designing for Intelligibility ........................................................................................ 1-2
Chapter 2 Background Information 2-1
Introduction .............................................................................................................. 2-1
In this Chapter ......................................................................................................... 2-1
Basic Audio Math......................................................................................................... 2-2
Ohm’s Law and the Decibel..................................................................................... 2-2
Adding Decibels....................................................................................................... 2-3
Sound and Hearing...................................................................................................... 2-4
The Relationship Between Sound and Hearing ...................................................... 2-4
The Nature of Speech ................................................................................................. 2-5
Introduction .............................................................................................................. 2-5
Consonants and Vowels.......................................................................................... 2-5
Room Acoustics........................................................................................................... 2-6
Introduction .............................................................................................................. 2-6
Reverberation .......................................................................................................... 2-6
Estimating Reverberation Times ............................................................................. 2-7
Countering the Effects of Reverberation ................................................................. 2-7
Speaker Basics............................................................................................................ 2-9
Inverse Square Law................................................................................................. 2-9
Sensitivity............................................................................................................... 2-10
Speaker Dispersion Angle and “Q”........................................................................ 2-10
Speaker Coverage................................................................................................. 2-12
Determining Critical Polar Angle............................................................................ 2-13
Determining Critical Polar Angle............................................................................ 2-14
Power Rating ......................................................................................................... 2-15
Speaker Layouts.................................................................................................... 2-15
Distributed Wall Mounted Systems............................................................................ 2-16
Introduction ............................................................................................................ 2-16
Advantages............................................................................................................ 2-16
Disadvantages ....................................................................................................... 2-16
Design of a Distributed Wall Mount System .......................................................... 2-17
Chapter 3 Speech Intelligibility 3-1
Introduction .............................................................................................................. 3-1
In this Chapter ......................................................................................................... 3-1
Table of Contents