Tyco 579-769 specifications Intelligibility

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Intelligibility

Intelligibility

Intelligibility has historically been a difficult parameter to measure. Unlike SPL that can easily be measured with a relatively common dBA meter, intelligibility measurements have previously required trained acoustical engineers or sophisticated/high end evaluations. NFPA 72 requires that voice messages to areas of buildings be intelligible without defining a preset limit within the main body (enforceable part) of NFPA 72.

From NFPA 72, 2002 Edition:

7.4.1.4* Where required, emergency voice/alarm communications systems shall be capable of the reproduction of prerecorded, synthesized, or live (e.g., microphone, telephone handset, and radio) messages with voice intelligibility.

Working without a preset limit gives the AHJ latitude to determine adequate intelligibility. NFPA 72 provides guidance for determining adequate intelligibility with the explanatory information in the Annex.

From NFPA 72, 2002 Edition:

A.7.4.1.4 Voice intelligibility should be measured in accordance with the guidelines in Annex A of IEC 60849, Second Edition: 1998, Sound systems for emergency purposes. When tested in accordance with Annex B, Clause B1, of IEC 60849, the system should exceed the equivalent of a common intelligibility scale (CIS) score of 0.70. Intelligibility is achieved when the quantity Iav-, as specified in B3 of IEC 60849, exceeds this value. Iav is the arithmetical average of the measured intelligibility values on the CIS and (sigma) is the standard deviation of the results. Objective means of determining intelligibility are found in Part 16 of IEC 60268, The objective rating of speech intelligibility by speech transmission index. Subject-based techniques for measuring intelligibility are defined by ANSI S3.2, Method for Measuring the Intelligibility of Speech Over Communications Systems. ANSI S3.2 should be considered an acceptable alternative to ISO TR 4870, where referenced in IEC 60268, Part 16, Second Edition: 1998, The objective rating of speech intelligibility by speech transmission index.

As technology for intelligibility analysis equipment advances, many expect the main body of NFPA 72 will be changed to require a minimum fixed intelligibility score, that is verifiable with the equipment designed for this purpose. The SimplexGrinnell STICIS meter and TALKBOX signal generator is the first such system developed to provide a measurement system that is nearly as easy to use as a dBA meter, provides readout in CIS units, and is portable.

Note: See the “Measures of Intelligibility” section in Chapter 3 of this guide for more information. The system uses a subset of the STI method outlined in IEC60628.

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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 Chapter Background Information Topic See Page #Equation 2-1. The Decibel Equation 2-3. Power RelationshipsBasic Audio Math Equation 2-2. Ohm’s LawEquation 2-5. dB and Sound Pressure Levels Equation 2-6. Adding DecibelsSound and Hearing Robinson and Dadson Equal Loudness CurvesNature of Speech Speech Pattern that Illustrates ModulationsRoom Acoustics Sabine Equation, used when α Eyring Equation, used when αAreas with high ceilings, specify a more directional speaker Speaker Basics Equation 2-8. The Inverse Square LawSPL = Sensitivity + 20 log Equation 2-9. On-Axis SPL Calculation87dB 6dB/divisionEquation 2-10. Directivity Factor Q for a Conical Source 51º 104 Critical Polar Angle CalculationsEquation 2-11. Coverage Area Calculations Listener Height = 1.5 Meters Ceiling Coverage Diameter2x Edge-to-Edge Layout Pattern Selection GuideSPL Variation by Layout Pattern Minimum OverlapDistributed Wall Mounted Systems Opposite Speaker WidthWall Mounted Speakers In Meters Room Coverage Width Edge-edge Minimum-Overlap Full-Overlap Chapter Speech Intelligibility Influences on Intelligibility Frequency of Speech Contribution to IntelligibilityDegradation of CIS vs. Signal-to-Noise Ratio No Noise With Added NoiseBackground Noise Reverberation Distortion Correlation of CIS and with STI and %ALcons Measures of IntelligibilityALcons STI method with faster measurement times Practical Measurement of Intelligibility STI-CIS Analyzer TalkboxTools for Predicting Intelligibility Page Chapter Emergency Voice/Alarm Communications Systems Typical Emergency Voice/Alarm Communications System AdvantagesParts of an Emergency Voice/Alarm Communications System Class a and B Speaker Circuit Wiring Chapter Regulatory Issues Audibility From Nfpa 72, 2002 EditionHigh Background Noise Large Areas Intelligibility Intelligibility Certification Page Chapter Speaker System Design Method Speaker Design Method Determine the speaker-to-listener distance D2Recommendations for Maximizing System Intelligibility Applying the Methods ITool Office Space ExampleOffice Space Speaker Location Guide Corridor Design Example Corridor Speaker Location Guide Corridor SPL DistributionITool 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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