Tyco 579-769 specifications Chapter Speech Intelligibility

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Introduction

In this Chapter

Chapter 3

Speech Intelligibility

Intelligibility is a measure of the capability of a message to be comprehended. In simplest terms, it is the reduction of the modulations of speech that reduce speech intelligibility. The modulation reductions can also be thought of as a reduction in the signal (the speech) to noise ratio.

Not all frequencies contained in speech contribute equally to intelligibility. While low frequencies (vowels) make up the largest power portion of the power of a speech signal, it is the higher frequencies (the consonants) that contribute most to intelligibility.

Refer to the page number listed in this table for information on a specific topic.

Topic	See Page #
Influences and Intelligibility	3-2
Measures of Intelligibility	3-6
Practical Measurement of Intelligibility	3-8
Tools for Predicting Intelligibility	3-9

3-1

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Contents Fire Alarm Audio Applications Guide Page Copyrights and Trademarks Page Table of Contents Emergency Voice/Alarm Communications Systems Glossary of Terms Related Publications Chapter Speech Intelligibility Overview Speech Intelligibility Importance Designing for Topic See Page # Chapter Background InformationBasic Audio Math Equation 2-3. Power RelationshipsEquation 2-1. The Decibel Equation 2-2. Ohm’s LawEquation 2-6. Adding Decibels Equation 2-5. dB and Sound Pressure LevelsRobinson and Dadson Equal Loudness Curves Sound and HearingSpeech Pattern that Illustrates Modulations Nature of SpeechRoom Acoustics Eyring Equation, used when α Sabine Equation, used when αAreas with high ceilings, specify a more directional speaker Equation 2-8. The Inverse Square Law Speaker BasicsEquation 2-9. On-Axis SPL Calculation SPL = Sensitivity + 20 logEquation 2-10. Directivity Factor Q for a Conical Source 6dB/division87dB 51º Critical Polar Angle Calculations 104Listener Height = 1.5 Meters Ceiling Coverage Diameter Equation 2-11. Coverage Area CalculationsSPL Variation by Layout Pattern Layout Pattern Selection Guide2x Edge-to-Edge Minimum OverlapDistributed Wall Mounted Systems Wall Mounted Speakers In Meters Room Coverage Width WidthOpposite Speaker Edge-edge Minimum-Overlap Full-Overlap Chapter Speech Intelligibility Frequency of Speech Contribution to Intelligibility Influences on IntelligibilityNo Noise With Added Noise Degradation of CIS vs. Signal-to-Noise RatioBackground Noise Reverberation Distortion ALcons Measures of IntelligibilityCorrelation of CIS and with STI and %ALcons STI method with faster measurement times STI-CIS Analyzer Talkbox Practical Measurement of IntelligibilityTools for Predicting Intelligibility Page Chapter Emergency Voice/Alarm Communications Systems Advantages Typical Emergency Voice/Alarm Communications SystemParts of an Emergency Voice/Alarm Communications System Class a and B Speaker Circuit Wiring Chapter Regulatory Issues From Nfpa 72, 2002 Edition AudibilityHigh Background Noise Large Areas Intelligibility Intelligibility Certification Page Chapter Speaker System Design Method Determine the speaker-to-listener distance D2 Speaker Design MethodRecommendations for Maximizing System Intelligibility ITool Office Space Example Applying the MethodsOffice Space Speaker Location Guide Corridor Design Example Corridor SPL Distribution Corridor Speaker Location GuideITool Gymnasium Example 10. Gymnasium Speaker Location Guide 13. Lobby Example 15. Lobby Layout Applying the Methods Conclusion Page Chapter Glossary of Terms Glossary Glossary Page Index IN-2 Page 579-769 Rev. C