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Fire Alarm
Audio Applications Guide
© 2005 Tyco Safety Products - Westminster. All rights reserved.
Printed in the U.S.A. All specifications and other information shown were current as of publication, and are subject to change without notice.
Guideline for
Designing Emergency
Voice/Alarm
Communications
Systems for Speech
Intelligibility
579-769
Rev. C
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Summary of Contents for Tyco Fire Alarm
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Page 1: Fire Alarm
Communications Systems for Speech Intelligibility 579-769 Rev. C © 2005 Tyco Safety Products - Westminster. All rights reserved. Printed in the U.S.A. All specifications and other information shown were current as of publication, and are subject to change without notice. - Page 3 Therefore, no warranty or representation is made about the sufficiency of any of the contents of this guide. Tyco Safety Products – Westminster, disclaims any and all liability for damages of any sort claimed to result from the use of this guide. This guide is distributed with no warranties whatsoever, including but not limited to, warranties of merchantability or fitness for a particular purpose.
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Page 5: Table Of Contents
Table of Contents Chapter 1 Speech Intelligibility Overview Introduction ......................1-1 Chapters of this Publication ..................1-1 In this Chapter ......................1-1 Importance of Audible and Intelligible Emergency Communications ......1-2 Speech Intelligibility Importance ................1-2 Designing for Intelligibility ..................1-2 Chapter 2 Background Information Introduction ...................... - Page 6 Influences on Intelligibility.................... 3-2 Introduction ......................3-2 Background Noise ....................3-3 Reverberation ......................3-4 Distortion........................3-5 Microphone Technique .................... 3-5 Measures of Intelligibility ..................... 3-6 Introduction ......................3-6 The Common Intelligibility Scale (CIS) ..............3-6 The STI Method ....................... 3-7 STIpa ........................
- Page 7 Step 1: Room Characteristics................6-2 Step 2: Calculate the Number of Speakers ............6-2 Step 3: Audio Power and Individual Speaker Wattage Tap ........6-2 Step 4: Model Design to Predict Intelligibility............6-2 Step 5: Verify Final Installation ................6-2 Recommendations for Maximizing System Intelligibility..........
- Page 8 Butterworth-Heinemann, Woburn, MA. • The Limits of Wide Dispersion (White Paper), Atlas Sound (www.atlassound.com). • National Fire Alarm Code (NFPA 72) 2002 Edition, published by National Fire Protection Association, (http://www.nfpacatalog.org/). • Objective Rating of Speech Intelligibility by Speech Transmission Index, International Electrotechnical Commission (IEC), 60268-16, Second Edition, 1998-03.
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Page 9: Chapter 1 Speech Intelligibility Overview
Fire Alarm Code intelligible and discusses methods for verifying intelligibility. In the past, the 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 building, or its furnishings. -
Page 10: Importance Of Audible And Intelligible Emergency Communications
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 recognized the importance of requiring both audibility and intelligibility. -
Page 11: Chapter 2 Background Information
Chapter 2 Background Information 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 exhaustive treatment of the subject. Note: Refer to the “Related Documentation”... -
Page 12: Basic Audio Math
Basic Audio Math Ohm’s Law Audio engineers use “Decibels” (dB) to express ratios between levels, such as power, Volts, and the Decibel 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 P and P ⎛... -
Page 13: Adding Decibels
Basic Audio Math, Continued Ohm’s Law When the decibel is used to express SPL, the reference sound pressure is 20 x 10 Newtons/m² and the Decibel, which is approximately the threshold for hearing for a normal listener. When using a dB meter to (continued) measure sound, the meter is performing the calculation between the received SPL and the reference SPL:... -
Page 14: Sound And Hearing
Sound and Hearing The Relationship Sound is created by mechanical vibrations that displace air molecules to create repetitive changes Between Sound in air pressure. The ear detects these changes in air pressure, with the magnitude of the pressure and Hearing perceived as loudness and the frequency of the changes perceived as pitch. -
Page 15: The Nature Of Speech
The Nature of Speech Introduction The frequency of speech ranges over seven octaves from 125 Hz to 8,000 Hz, with the majority of frequencies contributing to intelligibility falling between 500 Hz and 4,000 Hz. The creation of “phonemes,” or the sounds that make up words is created by amplitude modulation of those frequencies. -
Page 16: Introduction
Note: In the distributed speaker system typical of fire alarm applications, echoes are generally not a problem, but reverberation can have a major impact on intelligibility. -
Page 17: Estimating Reverberation Times
Room Acoustics, Continued Estimating Several equations are available for estimating the amount of reverberation that can be expected in Reverberation Times a room. The equations take into account the room dimensions and surface materials to provide a reasonably accurate estimation of a rectangular room’s reverberation time. The formulas below are commonly used Sabine and Eyring equations: The Sabine Equation, used when α... - 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.
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Page 19: Speaker Basics
Speaker Basics Inverse Square Law Speakers are essentially “point sources” of sound. Sound radiates outward in all directions, creating a spherical sound pattern. The sound pressure is spread over an increasingly larger surface area as the sound moves away from the source. This causes a drop in loudness per unit area. -
Page 20: Sensitivity
(SPL) produced by the speaker with a known signal frequency, power level and distance from the speaker. For fire alarm listed speakers approved under UL Standard 1480, the sensitivity is rated at 1 W of power and 10 feet (3 meters) from the speaker. By knowing the speaker’s sensitivity,... - Page 21 SPL. For the speaker above, the coverage angle is 150 degrees. Another common representation of speaker directivity is “Directivity Factor” or “Q.” For speakers having a conical coverage pattern (typical of single driver speakers used in fire alarm applications), “Q” is determined by: ⎛...
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Page 22: Speaker Coverage
Speaker Basics, Continued Speaker Coverage Using the polar information of the speaker, in combination with the distance between the speaker and the listener, you can determine the area that a speaker can cover. The “Coverage Area” is defined as the plane where the SPL at the edge of the plane drops 6 dB below the on-axis SPL, as illustrated below: Simplex 4902-9721 Ceiling Mount Speaker... -
Page 23: Determining Critical Polar Angle
Speaker Basics, Continued Speaker Coverage, Real world speakers have some polar loss at angles less than the rated dispersion angle. In order (continued) to determine the actual coverage area for a particular speaker, the “Critical Polar Angle” for the speaker must be found. The critical polar angle is the angle where the sum of the distance loss and the polar loss is 6 dB less than the on-axis SPL. - Page 24 Determining Critical Once the critical polar angle has been determined, calculate the coverage area for a given speaker- Polar Angle to-listener distance: ⎛ ⎞ θ ⎜ ⎟ Coverage Circle Diameter = 2 D ⎝ ⎠ ⎛ ⎞ ⎛ ⎞ θ π...
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Page 25: Power Rating
Speaker Basics, Continued Power Rating Speakers used for emergency voice/alarm communication system are wired as “Constant Voltage” systems, where the maximum power output of the amplifier is obtained at a certain speaker voltage, such as 25 V or 70.7 V. The power output of a speaker, and thus the resulting SPL is controlled by wattage taps on the speakers themselves. -
Page 26: Distributed Wall Mounted Systems
Distributed Wall Mounted Systems Introduction The preceding sections apply primarily to ceiling mounted speakers, generally referred to as “Distributed Overhead Systems.” Another useful mounting strategy is the “Distributed Wall Mount System.” Under this configuration, the speakers are placed on walls or columns, and are aimed into the room. -
Page 27: Design Of A Distributed Wall Mount System
Distributed Wall Mounted Systems, Continued Design of a The design of a distributed wall mount system is similar to an overhead system, with some Distributed Wall important differences. In a wall mount system the speaker-to-listener distance depends on the Mount System listener location in the room. - Page 28 Distributed Wall Mounted Systems, Continued Design of a The coverage patterns for a distributed wall mount system are similar to ceiling mount designs, Distributed Wall except only a single row is used in the pattern. Because of the typically larger potential speaker- Mount System, to-listener distance, only edge-to-edge and tighter spacing patterns should be used to provide (continued)
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Page 29: Chapter 3 Speech Intelligibility
Chapter 3 Speech Intelligibility Introduction Intelligibility is a measure of the capability of a message to be comprehended. In simplest terms, it is the reduction of the modulations of speech that reduce speech intelligibility. The modulation reductions can also be thought of as a reduction in the signal (the speech) to noise ratio. Not all frequencies contained in speech contribute equally to intelligibility. -
Page 30: Influences On Intelligibility
Influences on Intelligibility Introduction The figure below lists the relative contributions of each frequency band: Octave Band Contribution to Intelligibility 1000 2000 4000 8000 Frequency component of speech Figure 3-1. Frequency of Speech Contribution to Intelligibility Audibility is relatively straight-forward and deficiencies are relatively easy to correct. Intelligibility is a more complex characteristic of an installed audio system, involving room acoustics, speaker placement, and psycho-acoustic effects. -
Page 31: Background Noise
Influences on Intelligibility, Continued Background Noise Background noise causes a reduction in signal-to-noise ratio over all frequencies and modulations. Consider the comparison of the speech signal below with and without added noise: No Noise With Added Noise Figure 3-2. The Speech Pattern “An Emergency Has Been Reported” with Added Noise Creating an intelligible system in the presence of background noise requires adequate signal-to- noise ratio. -
Page 32: Reverberation
Influences on Intelligibility, Continued Background Noise, Some types of background noise have a greater impact on intelligibility than others depending on (continued) the frequency content of the noise. Noise generated by several conversations occurring simultaneously, such as in areas of public assembly, (an airport terminal or shopping mall) generally require a higher signal-to-noise ratio than noise generated by HVAC units. -
Page 33: Distortion
“Clipping” is caused by some part of the electrical signal path within the fire alarm system exceeding the capacity of the components. The most common cause of clipping is improper use of the microphone, where the operator is shouting into the microphone, overdriving the system. -
Page 34: Measures Of Intelligibility
Measures of Intelligibility Introduction International Electrotechnical Commission (IEC) 60849 defines intelligibility as: “a measure of the proportion of the content of a speech message that can be correctly understood.” Because “understanding” involves evaluation by a human, intelligibility is by definition difficult to quantify absolutely. -
Page 35: The Sti Method
Measures of Intelligibility, Continued The STI Method As described in Chapter 2, speech consists of the frequency of the sound being uttered and the amplitude modulation of that sound into the phonemes that create words. The STI (Speech Transmission Index) method measures the modulation transfer function for 14 modulation frequency bands spaced at 1/3-octave intervals from 0.63 Hz to 12.5 Hz, across seven frequency bands from 125 Hz to 8 KHz. -
Page 36: Practical Measurement Of Intelligibility
Practical Measurement of Intelligibility Introduction Measurement of intelligibility can be complicated, and it sometimes includes subjective analysis. To effectively implement intelligible systems in real buildings requires that a simple, accurate, and repeatable method of measuring intelligibility must be available. Fortunately, there are instruments on the market that meet this need. -
Page 37: Tools For Predicting Intelligibility
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. - Page 38 3-10...
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Page 39: Chapter 4 Emergency Voice/Alarm Communications Systems
Chapter 4 Emergency Voice/Alarm Communications Systems Introduction An emergency voice/alarm communications system is designed to provide a highly reliable voice reinforcement and distribution network. These systems must deliver messages to building occupants for evacuation in an organized and safe manner. The system can deliver recorded messages automatically before emergency personnel arrive at the scene, and alarm paging systems can also be used to deliver live spoken messages from the emergency personnel to the occupants. -
Page 40: A Typical Emergency Voice/Alarm Communications System
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. •... -
Page 41: Parts Of An Emergency Voice/Alarm Communications System
Parts of an Emergency Voice/Alarm Communications System Command Center A command center should be located at the building entrance and act as a communications center for emergency personnel. The command center is used to display the system status and control the annunciation system. -
Page 42: Speaker Circuits
Speaker circuits are known as constant voltage systems, where a full volume output tone produce 25 V or 70.7 V. Wattage taps on the speaker sets the individual speaker volume. The designer can select from 1/4 W to 2 W in a typical fire alarm speaker. Class A Wiring... -
Page 43: Chapter 5 Regulatory Issues
Chapter 5 Regulatory Issues Introduction The governing specifications for the US Fire Alarm Market are found in the installation standard, ® NFPA 72 “National Fire Alarm Code.” The fire alarm audio system is defined within the class of “Notification Appliances.” NFPA 72 defines, among other things, requirements for audibility and intelligibility. -
Page 44: Audibility
Audibility Tones and SPL For emergency messages to be heard, NFPA 72 suggests that the sound level of the emergency evacuation tone to be measured at 5-feet. This is the average “ear level” of someone standing. The messages must be 15 dBA above normal ambient sound or 5 dBA above sounds lasting longer than 60 seconds. -
Page 45: High Background Noise
Audibility, Continued High Background To meet the 15 dBA requirement, there are cases where high levels of background noise require Noise 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. -
Page 46: Intelligibility
Intelligibility Intelligibility Intelligibility has historically been a difficult parameter to measure. Unlike SPL that can easily be measured with a relatively common dBA meter, intelligibility measurements have previously required trained acoustical engineers or sophisticated/high end evaluations. NFPA 72 requires that voice messages to areas of buildings be intelligible without defining a preset limit within the main body (enforceable part) of NFPA 72. -
Page 47: Intelligibility Certification
Intelligibility, Continued Intelligibility, There is significant explanatory information in Annex A, recently revised for the 2002 edition: (continued) From NFPA 72, 2002 Edition: A.7.4.1.4. The designer of an intelligible voice/alarm system should possess skills sufficient to properly design a voice/alarm system for the occupancy to be protected. System designs for many smaller occupancies can be accomplished satisfactorily, if not optimally, based upon experience with the performance of other systems in similar spaces. -
Page 49: Chapter 6 Speaker System Design Method
Chapter 6 Speaker System Design Method Introduction This chapter covers a design methodology that can be used to design a speaker system for an emergency voice/alarm communications system. The ability to design an emergency voice/alarm communications system which is highly intelligible at a reasonable cost, represents a significant advantage to the customer. -
Page 50: Speaker Design Method
Introduction The steps below summarize the speaker system design method. Use these steps in conjunction with the Tyco Safety Products iTool (described later in this chapter). Step 1: Determine if the room requires advanced design methods. Some characteristics of a difficult... -
Page 51: Recommendations For Maximizing System Intelligibility
Recommendations for Maximizing System Intelligibility Maximizing Use the following recommendations to maximize system intelligibility: Intelligibility • Ensure at least an 8 dBA signal-to-noise ratio with regard to the speech signal. Note: This can result in a higher than 15 dB signal-to-noise ratio for notification tones. If the notification tones become too loud for a particular location, consider reducing the volume of the tone with respect to the speech signal. -
Page 52: Applying The Methods
Design Examples The following examples illustrate the design methodology outlined earlier in this chapter. For these examples, computer based modeling was employed using Tyco Safety Products “iTool” to demonstrate intelligibility. Note: See the iTool Installation and User’s Guide (579-772) for iTool installation and operation instructions. -
Page 53: Example 1: Office Space
Applying the Methods, Continued Example 1: Click the “Speaker Location” tab on the iTool for more detailed information. The following Office Space, screen shows a speaker location guide for the office space: (continued) Speaker Location Tab Figure 6-2. Office Space Speaker Location Guide SPL distribution information, reverberation time results, and speaker coverage information are also available: Figure 6-3. -
Page 54: Example 2: Corridor
Applying the Methods, Continued Example 2: Corridor In this example, consider a standard office corridor with the following specifications: • 100’ L x 12’ W x10’ H Dimensions = • Tile Flooring = • Acoustic Tile Ceiling = • Gypsum over 2” x 4”, (16” on center) Walls = •... - Page 55 Applying the Methods, Continued Example 2: Corridor, Click the “Speaker Location” button on the iTool for more detailed information. The following (continued) screen shows a speaker location guide for the corridor: Figure 6-6. Corridor Speaker Location Guide SPL distribution information, reverberation time results, and speaker coverage information are also available: Figure 6-8.
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Page 56: Example 3: Gymnasium
Applying the Methods, Continued Example 3: Gymnasiums are notoriously bad acoustic environments. Extremely high reverberation times can Gymnasium be expected because of the large room volume plus the hard walls, wood floors, and plaster or metal ceilings. Gymnasiums typically require surface treatments and sound absorbers and specialized speaker clusters and/or speakers with high Q values. - Page 57 Applying the Methods, Continued Example 3: Click the “Speaker Location” button on the iTool for more detailed information. The following Gymnasium, screen shows a speaker location guide for the gymnasium: (continued) Figure 6-10. Gymnasium Speaker Location Guide SPL distribution information, reverberation time results, and speaker coverage information are also available: Figure 6-12.
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Page 58: Example 4: Lobby
Applying the Methods, Continued Example 4: During an intelligibility survey in an office building, an employee lobby area measured 0.60 CIS Lobby intelligibility, failing the NFPA suggested 0.70. This room is characterized by tile floor, hard walls, and one wall made up mostly of glass, see the figure below. The SPL is adequate at 79 dB for an average background noise level of 47 dB. - Page 59 Applying the Methods, Continued Example 4: The existing design had two wall mounted speakers, to the left and right of the entrance doors. Lobby, (continued) Command Center Stairwell Reception Desk Figure 6-15. Lobby Layout The following screens below show the lobby speaker location guide and the SPL distribution for the lobby: Figure 6-16.
- Page 60 Applying the Methods, Continued Example 4: The following screen shows the reverberation time and speaker coverage information: Lobby, (continued) Figure 6-18. Lobby Reverberation Time and Speaker Coverage Information 6-12...
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Page 61: Conclusion
Conclusion In Closing Designing Emergency Voice/Alarm Communications Systems for Speech Intelligibility requires awareness of the area dimensions, anticipated background noise level; wall, ceiling, and floor materials; anticipated occupancy, and any other characteristics that may influence the desired acoustical properties. This guide has presented a summary of those considerations in order to better understand the concept of speech intelligibility. - Page 62 6-14...
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Page 63: Chapter 7 Glossary Of Terms
Chapter 7 Glossary of Terms Introduction This chapter contains a glossary of technical terms that are used throughout this manual. In this Chapter Refer to the page number listed in this table for information on a specific topic. Topic See Page # Glossary... -
Page 64: Glossary
AHJ – The “Authority Having Jurisdiction” is the organization or person responsible for approving fire alarm installations for occupancy. AUDIBILITY – A measure of loudness of a sound. When used with respect to fire alarm systems, audibility is regarded as the evacuation signal level above background noise. - Page 65 NFPA – The “National Fire Protection Agency (NFPA)” is the organization responsible for several codes and guidelines related to the Fire Alarm/Protection Industry. Many of these codes are referenced and discussed in this publication. OCTAVE – A tone that is eight full tones (diatonic degrees) above or below another given tone.
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Page 67: Index
2-4 Sabine and Eyring equations, 2-7 sensitivity, 7-3 fiber optic riser, 7-3 signal-to-noise ratio, increasing, 2-8 fire alarm audio systems, 4-3 sound pressure levels (SPL), 7-3 frequency, 7-3 Sound Pressure Levels (SPL), 2-2 speaker circuits, 4-4 speaker coverage, 2-12... - Page 68 speaker dispersion angle, 2-10 Speaker layout patterns, 2-15 transponder, 4-3, 7-3 speaker placement, 2-7 speaker, sensitivity, 2-10 speech pattern, 3-4 speech pattern, modulations, 2-5 voice alarm systems, 4-2 STI method, 3-7, 7-3 STI-CIS Intelligibility Measurement System, 3-8 wall mounted speakers, 2-16 STIpa, 3-7 wall mounted speakers, advantages, 2-16 STITEL, 3-7...
- Page 70 579-769 Rev. C Printed in the U.S.A. Specifications and other information shown were current as of publication, and are subject to change without notice. © 2005 Tyco Safety Products – Westminster. All rights reserved.
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