1、NEMA Standards PublicationNational Electrical Manufacturers AssociationNEMA SB 50-2014Emergency Communications Audio Intelligibility Applications Guide NEMA SB 50-2014 Emergency Communications Audio Intelligibility Applications Guide Published by: National Electrical Manufacturers Association 1300 N
2、orth 17th Street, Suite 900 Rosslyn, Virginia 22209 www.nema.org Copyright 2014 by the National Electrical Manufacturers Association. All rights including translation into other languages, reserved under the Universal Copyright Convention, the Berne Convention for the Protection of Literary and Arti
3、stic Works, and the International and Pan American Copyright Conventions. NOTICE AND DISCLAIMER The information in this publication was considered technically sound by the consensus of persons engaged in the development and approval of the document at the time it was developed. Consensus does not ne
4、cessarily mean that there is unanimous agreement among every person participating in the development of this document. NEMA standards and guideline publications, of which the document contained herein is one, are developed through a voluntary consensus standards development process. This process bri
5、ngs together volunteers and/or seeks out the views of persons who have an interest in the topic covered by this publication. While NEMA administers the process and establishes rules to promote fairness in the development of consensus, it does not write the document and it does not independently test
6、, evaluate, or verify the accuracy or completeness of any information or the soundness of any judgments contained in its standards and guideline publications. NEMA disclaims liability for any personal injury, property, or other damages of any nature whatsoever, whether special, indirect, consequenti
7、al, or compensatory, directly or indirectly resulting from the publication, use of, application, or reliance on this document. NEMA disclaims and makes no guaranty or warranty, expressed or implied, as to the accuracy or completeness of any information published herein, and disclaims and makes no wa
8、rranty that the information in this document will fulfill any of your particular purposes or needs. NEMA does not undertake to guarantee the performance of any individual manufacturer or sellers products or services by virtue of this standard or guide. In publishing and making this document availabl
9、e, NEMA is not undertaking to render professional or other services for or on behalf of any person or entity, nor is NEMA undertaking to perform any duty owed by any person or entity to someone else. Anyone using this document should rely on his or her own independent judgment or, as appropriate, se
10、ek the advice of a competent professional in determining the exercise of reasonable care in any given circumstances. Information and other standards on the topic covered by this publication may be available from other sources, which the user may wish to consult for additional views or information no
11、t covered by this publication. NEMA has no power, nor does it undertake to police or enforce compliance with the contents of this document. NEMA does not certify, test, or inspect products, designs, or installations for safety or health purposes. Any certification or other statement of compliance wi
12、th any health or safety-related information in this document shall not be attributable to NEMA and is solely the responsibility of the certifier or maker of the statement. SB 50-2014 Page i 2014 National Electrical Manufacturers Association Contents Foreword iii Scope . iii Acknowledgment . iii Sect
13、ion 1 Speech Intelligibility Overview . 1 1.1 Introduction 1 1.1.1 Chapters of This Publication 1 1.2 Importance of Audible and Intelligible Emergency Communications 1 1.2.1 Speech Intelligibility Importance 1 1.2.2 Designing for Intelligibility 2 Section 2 Background Information . 3 2.1 Introductio
14、n 3 2.2 Basic Audio Math . 3 2.2.1 Ohms Law and the Decibel. 3 2.2.2 Adding Decibels . 4 2.3 Sound and Hearing 5 2.3.1 The Relationship between Sound and Hearing . 5 2.4 The Nature of Speech . 6 2.4.1 Introduction 6 2.4.2 Consonants and Vowels 6 2.5 Room Acoustics . 7 2.5.1 Introduction 7 2.5.2 Reve
15、rberation 7 2.5.3 Estimating Reverberation Times . 7 2.5.4 Countering the Effects of Reverberation . 8 2.6 Speaker Basics 9 2.6.1 Inverse Square Law . 9 2.6.2 Sensitivity. 10 2.6.3 Speaker Dispersion Angle and “Q” 10 2.6.4 Speaker Coverage . 11 2.6.5 Determining Critical Polar Angle . 13 2.6.6 Deter
16、mining Critical Polar Angle . 14 2.6.7 Power Rating . 14 2.6.8 Speaker Layouts 15 2.7 Distributed Wall-Mounted Systems . 16 2.7.1 Introduction 16 2.7.2 Advantages 16 2.7.3 Disadvantages . 17 2.7.4 Design of a Distributed Wall-Mount System 17 Section 3 SPEECH INTELLIGIBILITY 19 3.1 Introduction 19 3.
17、2 Influences on Intelligibility 19 3.2.1 Introduction 19 3.2.2 Background Noise . 20 3.2.3 Reverberation 21 3.2.4 Distortion 22 3.2.5 Microphone Technique 22 3.3 Measures of Intelligibility . 22 3.3.1 Defining Intelligibility 22 3.3.2 Measuring Intelligibility 22 3.3.3 The Common Intelligibility Sca
18、le (CIS) 23 SB 50-2014 Page ii 2014 National Electrical Manufacturers Association 3.4 Recommendations for Maximizing System Intelligibility 23 3.4.1 Maximizing Intelligibility . 23 3.5 Conclusion . 23 Tables 2-1 Examples of Typical 4-inch Speaker Coverage for Varying Ceiling Heights 14 2-2 Layout Pa
19、ttern Selection Guide 15 2-3 SPL Variation by Layout Pattern . 15 2-4 Wall-Mounted Speaker Coverage Width vs. Room Depth . 18 Figures 2-1 Robinson and Dadson Equal Loudness Curves . 5 2-2 Speech Pattern that Illustrates Modulations . 6 2-3 dB and Distance Chart 9 2-4 Speaker Polar Plot Interpretatio
20、n 11 2-5 Speaker Coverage 12 2-6 Maximum Theoretical Coverage Angle . 12 2-7 Critical Polar Angle Calculations . 13 2-7 Speaker Layout Patterns 16 2-8 Wall-Mount Speaker Coverage Pattern 17 2-9 Typical Wall-Mount Speaker Coverage Layouts 18 3-1 Frequency of Speech Contribution to Intelligibility 19
21、3-2 The Speech Pattern “An Emergency Has Been Reported” with Added Nois . 20 3-3 Degradation of CIS vs. Signal-to-Noise Ratio. 21 3-4 The Speech Pattern “An Emergency Has Been Reported” with Reverberation . 22 Equations 2-1 The Decibel . 3 2-2 Ohms Law 3 2-3 Power Relationships . 3 2-4 dB and Voltag
22、es 4 2-5 dB and Sound Pressure Levels 4 2-6 Adding Decibels 5 2-7 Sabine and Eyring Formulas for Calculating Reverberation Times 8 2-8 The Inverse Square Law . 9 2-9 On-Axis SPL Calculation. 10 2-10 Directivity Factor “Q” for a Conical Source . 11 2-11 Coverage Area Calculations . 14 SB 50-2014 Page
23、 iii 2014 National Electrical Manufacturers Association Foreword Emergency voice communications are extensively used to provide building occupants information and instructions during emergencies. These messages contain vital safety information that must be clearly understood by the building occupant
24、s. Consequently intelligibility of these paging systems has become a vital concern. This guide was developed to assist specifiers and Jurisdictional Authorities that are not experts in Acoustics understand the basic concepts that impact intelligibility. Proposed or recommended revisions should be su
25、bmitted to: Senior Technical Director, Operations National Electrical Manufacturers Association 1300 North 17th Street, Suite 900 Rosslyn, Virginia 22209 www.nema.org Scope NEMA has created this guide to assist specifiers and Authorities Having Jurisdiction understand the concepts and terminology ut
26、ilized to enhance intelligibility for emergency voice paging systems. This is not nor is it intended to be a comprehensive treatment of the subject matter. Rather, it provides an overview of issues and general recommendations to enhance intelligibility. Acknowledgement NEMA acknowledges Tycos Fire A
27、larm Audio Applications Guide as the principal source material for this NEMA Standard. Text is being used and republished by NEMA with permission from Tyco. SB 50-2014 Page iv 2014 National Electrical Manufacturers Association SB 50-2014 Page 1 2014 National Electrical Manufacturers Association Sect
28、ion 1 Speech Intelligibility Overview 1.1 INTRODUCTION Intelligibility The capability of being understood or comprehended. In simple terms, intelligibility is an evaluation of changes that occur to speech that impact comprehension. More specifically, intelligibility is concerned with evaluating redu
29、ctions of the modulations of speech that cause undesired reductions in speech comprehension. These modulation reductions can also be thought of as a degradation of signal (speech) to noise ratio. Over the last few years, the drive towards intelligible Emergency Voice/Alarm Communications Systems has
30、 been gaining momentum throughout the fire alarm industry. NFPA 72 The National Fire Alarm and Signaling Code now requires that emergency voice/alarm communications systems be capable of producing messages with voice intelligibility and discusses methods for verifying intelligibility. In the past, t
31、he fire alarm industry primarily focused concern on audibility requirements, assuming that if the sound was loud enough it would be sufficiently intelligible. Furthermore, many designs did not take into account ongoing changes in the construction of the building, the construction materials used in a
32、 building, or its furnishings. It is possible that many emergency voice/alarm communications systems designed under those conditions do not provide sufficiently intelligible communications. While those systems may provide highly audible alert and evacuation tones, speech information may not be prope
33、rly delivered. This guide provides general information on the concepts of intelligibility and on the design of emergency voice/alarm communications systems. It provides you with a better understanding of the factors affecting the intelligibility of these systems in public spaces and is intended to h
34、elp design a system that meets the requirements for speech audibility and intelligibility in a cost effective manner. 1.1.1 Chapters of This Publication This guide is separated into the following chapters: Chapter 1. Speech Intelligibility Overview: Provides an overview of audio intelligibility and
35、an introduction to the topics covered in this publication. Chapter 2. Background Information: Provides several sections of background material that are essential to designing an intelligible system. Topics such as room acoustics, speaker design layouts, and audio math are discussed. Chapter 3. Speec
36、h Intelligibility: Details the influences and measurements of intelligibility. 1.2 IMPORTANCE OF AUDIBLE AND INTELLIGIBLE EMERGENCY COMMUNICATIONS 1.2.1 Speech Intelligibility Importance Emergency voice/alarm communications systems are used in applications where it is necessary to communicate more d
37、etailed information to occupants of a building than the simple evacuation signal provided by horns or bells. For example, in a high-rise building, evacuation of all of the occupants at one time could create an unsafe situation in which the routes to evacuation could be blocked by the sheer number of
38、 people trying to exit at once. SB 50-2014 Page 2 2014 National Electrical Manufacturers Association An emergency voice/alarm communications system can provide a means to ensure a more orderly and safe evacuation. However, if the emergency voice/alarm communications system is not audible (loud enoug
39、h), or if it is not intelligible (understandable), then emergency information is not properly communicated. Therefore, a safe response to an emergency cannot be reliably achieved. In some ways an inaudible or unintelligible system is worse than not having a system. This is due to a possible false se
40、nse of security. Also personnel responding to an incident may operate under the premise that building occupants are getting proper instructions, when in reality they are not. Historically, the emphasis in emergency voice/alarm communications system design has been on audibility. These systems have b
41、een required to have a sound level that is at least 15 dB above the average ambient sound level, or 5 dB above the maximum sound level having a duration of at least 60 seconds, whichever is greater. Starting with the 1999 version of the National Fire Alarm Code (NFPA 72) the fire alarm industry reco
42、gnized the importance of requiring both audibility and intelligibility. 1.2.2 Designing for Intelligibility Properly designing emergency voice/alarm communications systems for intelligibility requires knowledge of the acoustical factors that influence intelligibility; awareness of the tools availabl
43、e to predict acoustical performance; and the ability to measure the intelligibility of the completed installation. It is also necessary to identify complicated areas where experienced sound professionals using sophisticated audio design tools may be required to achieve the desired intelligibility. T
44、his document is presented as an introductory guide to understanding intelligibility and its importance in achieving successful emergency voice/alarm communications systems. Please refer to the cited references for more information concerning audio systems design. SB 50-2014 Page 3 2014 National Elec
45、trical Manufacturers Association Section 2 Background Information 2.1 INTRODUCTION There are a few fundamental concepts that are necessary to understand when working with emergency voice/alarm communications systems. This chapter introduces basic concepts of sound, but is not intended to be an exhau
46、stive treatment of the subject. NOTERefer to the “Related Documentation” section at the beginning of this standard for publications containing in-depth discussions of sound and speech. 2.2 BASIC AUDIO MATH 2.2.1 Ohms Law and the Decibel Audio engineers use “Decibels” (dB) to express ratios between l
47、evels, such as power, Volts, Amps, and Sound Pressure Levels (SPL). The decibel is not an absolute measure like Volts and Amps, rather it is used to make comparisons between two numbers. The decibel is defined as the logarithm of two power levels, shown below in the equation as P1 and P0: 01PPlo g10
48、 D e cib e l Equation 2-1 The Decibel P0 is the reference power and P1 is the power level used for comparison. The logarithm is used in the decibel in order to make comparisons of power over a very wide range. This is very useful in audio applications as the ear responds logarithmically to changes i
49、n SPL. You can also use the decibel for voltage comparisons. From Ohms Law we know that: RIV Equation 2-2 Ohms Law The electrical power equation: RIPRVPIVP 22 Equation 2-3 Power Relationships Where: V = Volts I = Amps R = Resistance SB 50-2014 Page 4 2014 National Electrical Manufacturers Association Use the following equation to determine the decibel difference between two voltage measurements powering the same load resistance: 012021VVl o g20dB:tos i m p l i f i e dbec a nw h i c hRV RVl o g10dB Equation
