Tyco 579-769 specifications High Background Noise Large Areas

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Audibility, Continued

High Background Noise

Large Areas

To meet the 15 dBA requirement, there are cases where high levels of background noise require extremely high levels of emergency annunciation to overcome the noise. When background noise exceeds 105 dBA or when the SPL calculations require greater than 110 dBA, the use of visual notification appliances is warranted.

There are cases where the background noise can be reduced or eliminated by allowing the emergency voice/alarm communications system to remove the source of the noise. For example, background music can be disabled during an alarm condition.

Very large areas such as arenas pose a particular challenge to meeting NFPA 72 requirements. These areas have sound systems installed that produce tens of thousands watts of power, however these systems are not typically designed to meet NFPA 72 requirements. If the systems are engineered to provide adequate SPL and intelligibility then it would make sense from a performance perspective to use the systems for emergency evacuation. By working closely with the AHJ and the building’s owner, it may be possible to allow the use of the existing PA system. However, some modifications may be required.

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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