Tyco 579-769 specifications Areas with high ceilings, specify a more directional speaker

Page 18

Room Acoustics, Continued

Countering the

Increasing the Signal-to-Noise Ratio:

Effects of

Intelligibility degradation from reverberation is essentially a signal-to-noise issue, however

Reverberation,

when the noise is specifically caused by reverberation it is referred to as the “Direct-to-

(continued)

 

Reverberant” ratio. Increasing the direct sound field at the listener improves the direct to

 

reverberant ratio and therefore the signal-to-noise ratio. You can increase the direct sound in

 

several ways:

 

1. Move the speaker closer to the listener and reduce the wattage of the speaker:

 

This places the sound where it is needed and minimizes excitation of the room’s

 

reverberation, at the expense of additional speakers.

 

2. Increase the speaker density and reduce the wattage to each speaker:

 

This increases the direct sound heard by the listener by creating overlapping regions

 

of coverage.

 

3. In areas with high ceilings, specify a more directional speaker:

 

A speaker that is more focused (has a higher “Q”) concentrates most of the sound energy

 

in a tighter beam than low “Q” devices. This is important in areas with high ceilings to

 

reduce the effect of multiple late arriving sounds.

 

Note: See the section later in this chapter entitled “Speaker Dispersion Angle and ‘Q’”

 

for more information.

2-8

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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 Calculation6dB/division 87dBEquation 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 Width Opposite SpeakerWall 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 Measures of Intelligibility Correlation of CIS and with STI and %ALconsALcons 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