Tyco 579-769 specifications Typical Emergency Voice/Alarm Communications System, Advantages

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A Typical Emergency Voice/Alarm Communications System

Typical Emergency	The figure below illustrates a typical emergency voice/alarm communications system:
Voice/Alarm
Communications
Communications
System

			Figure 4-1. Typical Emergency Voice/Alarm Communications System
	Advantages	While an emergency voice/alarm communications system is similar to a non-emergency paging
	Advantages	system, there are certain features that make emergency systems much more reliable than standard

		paging systems:
		• Backup Power Source (Batteries or Generator):
			Allows the system to operate for as long as several days during a power failure.
		•	Dedicated Power Feed:
			Isolates fire alarm power circuits from other branch circuits, preventing a fault from a
			non-alarm circuit causing a fault at the fire alarm.
		• Supervision of All Critical Signal Paths:
			From the microphone through the last speaker in the system, all wiring is supervised for
			shorts, opens, and Earth faults.
		•	Access Control:
			Locked cabinet permits only authorized personnel to access to the system.
		•	Fixed Gain Controls:
			The system is factory calibrated and sealed to prevent the user from tampering with the gain,
			avoiding over-driving or under-driving the system.
		•	Local Mode Operation:
			Alarm signals are available even if amplifiers lose communications with the command center.

4-2

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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 2-3. Power Relationships Basic Audio MathEquation 2-1. The Decibel 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 DiameterLayout Pattern Selection Guide SPL Variation by Layout Pattern2x 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 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