Tyco 579-769 specifications Tools for Predicting Intelligibility

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Tools for Predicting Intelligibility

Introduction

Acoustical Modeling Software

Several tools varying in levels of complexity can assist the sound system designer in producing a system of acceptable intelligibility. These range from simple layout guides for speaker placement to complex computer modeling tools which can accurately simulate and predict sound system performance in complex spaces. These tools also have the ability to listen to simulations of system performances at any location within the space.

The tools selected should be based on the complexity and characteristics of the particular installation. In many cases, layout guides and “rules of thumb” are adequate to produce an effective design. In other cases, sophisticated modeling and analysis is necessary.

There are a number of computer modeling and simulation tools available to the sound system designer that provides reliable predictions of speech intelligibility and audio coverage throughout the modeled space. These tools can help the designer through difficult situations or in designing emergency voice/alarm communications system for spaces with complex audio environments.

The best known and widely used of these modeling programs is “EASE” from Renkus-Heinz®. Another program is “Modeler” available from Bose® Corporation. Both of these programs have shown good correlation between predicted results and actual measurements when the system is modeled accurately. These programs provide a reliable means to confidently design and build more complicated systems that require minimum speech intelligibility levels.

The two listed programs require significant training and expertise to use, as well as a fair amount of time to build models that are complete enough to provide accurate results. For small to medium sized projects, it usually is not cost effective to use these modeling tools. However, for larger or more complex projects, the costs of modeling tools are easily justified. It is much less expensive to use the modeling tools to design the system properly the first time than to have to troubleshoot problems after installation.

For the smaller projects typical in a fire alarm layout, Tyco Safety Products has developed software called “iTool” that can be used to design a speaker system that meet requirements for most areas. This tool is not an acoustical modeling package. It is designed to assist the Speaker System Designer with calculations of reverberation and assist with speaker placement.

Note: See Chapter 6 of this manual for design examples that use the iTool. Refer to the iTool Installation and User’s Guide (579-772) for more information.

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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 log87dB 6dB/divisionEquation 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 Opposite Speaker WidthWall 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 Correlation of CIS and with STI and %ALcons Measures of IntelligibilityALcons 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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