Tyco 579-769 specifications Chapter Speech Intelligibility Overview

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Introduction

Chapters of this Publication

In this Chapter

Chapter 1

Speech Intelligibility Overview

INTELLIGIBILITY – The capability of being understood or comprehended.

In simple terms, intelligibility is an evaluation of changes that occur to speech that impact comprehension. More specifically, intelligibility is concerned with evaluating reductions of the modulations of speech that cause undesired reductions in speech comprehension. These modulation reductions can also be thought of as a degradation of signal (speech) to noise ratio.

Over the last few years, the drive towards intelligible Emergency Voice/Alarm Communications Systems has been gaining momentum throughout the fire alarm industry. NFPA 72®, the National Fire Alarm Code® now requires that emergency voice/alarm communications systems be intelligible and discusses methods for verifying intelligibility.

In the past, the fire alarm industry primarily focused concern on audibility requirements, assuming that if the sound was loud enough it would be sufficiently intelligible. Furthermore, many designs did not take into account ongoing changes in the construction of the building, the construction materials used in a building, or its furnishings. It is possible that many emergency voice/alarm communications systems designed under those conditions do not provide sufficiently intelligible communications. While those systems may provide highly audible alert and evacuation tones, speech information may not be properly delivered.

This guide provides general information on the concepts of intelligibility and on the design of emergency voice/alarm communications systems. It provides you with a better understanding of the factors affecting the intelligibility of these systems in public spaces and is intended to help design a system that meets the requirements for speech audibility and intelligibility in a cost-effective manner.

This guide is separated into the following chapters:

•Chapter 1. Speech Intelligibility Overview: Provides an overview of audio intelligibility and an introduction to the topics covered in this publication.

•Chapter 2. Background Information: Provides several sections of background material that are essential to designing an intelligible system. Topics such as room acoustics, speaker design layouts, and audio math are discussed.

•Chapter 3. Speech Intelligibility: Details the influences and measurements of intelligibility.

•Chapter 4. Emergency Voice/Alarm Communication Systems: Details emergency voice/alarm communications systems and describes the advantages of an emergency system compared to a typical non-emergency paging system.

•Chapter 5. Regulatory Issues: Discusses National Fire Protection Agency (NFPA) Codes. Several excerpts of the 2002 Code are included.

•Chapter 6. Fire Alarm Audio Speaker System Design Method: Provides examples of speaker designs created by using the Tyco Safety Products iTool.

•Chapter 7. Glossary of Terms: This chapter includes definitions of the important terms used in this publication.

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

Topic

See Page #

Importance of Audible and Intelligible Emergency Communications

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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 log6dB/division 87dBEquation 2-10. Directivity Factor Q for a Conical Source 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 Width Opposite SpeakerWall Mounted Speakers In Meters Room Coverage Width 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 Measures of Intelligibility Correlation of CIS and with STI and %ALconsALcons 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
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