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Tyco 579-769 User's Manual

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1. Some observations about speaker coverage area e Low ceilings require more speakers per square foot of floor space than high ceilings e The Simplex 4902 series 4 inch speakers cover an area with a diameter slightly larger than twice the distance from the ear to the ceiling e The smaller the speaker the wider the dispersion therefore the larger the coverage area Continued on next page 2 14 Speaker Basics Continued Power Rating Speaker Layouts 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 The minimum wattage tap for a UL Standard 1480 listed speaker is 1 4 W For example the Simplex 4902 Series speakers have wattage taps in 3 dB increments 1 4 W 1 2 W 1 W and 2 W Each wattage tap doubles the power delivered by the speaker and so increases the SPL output by 3 dB for each increasing tap An increase of 3 dB is considered a just noticeable increase in SPL changing the wattage tap from 1 4 W to 2 W increases the perceived loudness by slightly less than double Many rooms require more than one speaker the question then becomes how many speakers do I need and how far apart should they be placed
2. 0 0 dB 0 1 dB 0 5 dB 1 2 dB 2 3 dB 3 8 dB 6 0 dB 6dB Point 52 Critical Polar Angle 104 Notes 1 Polar Loss interpreted from polar plot 2 Distance Loss calculated as 20 log cos 8 Figure 2 7 Critical Polar Angle Calculations Continued on next page 2 13 Determining Critical Once the critical polar angle has been determined calculate the coverage area for a given speaker Polar Angle to listener distance Coverage Circle Diameter 2 D tan gt 2 Coverage Area T o tan 3 Where D is the distance from the speaker to the listener and 6 is the critical polar angle Refer to Figure 2 5 Speaker Coverage Diagram Equation 2 11 Coverage Area Calculations The following table contains coverage areas calculated for Simplex TrueAlert Ceiling Mount speakers at various ceiling heights with a listener height of 5 feet 1 5 meters Table 2 1 Simplex 4902 Speaker Coverage for Varying Ceiling Heights Listener Height 5 Feet Listener Height 1 5 Meters Ceiling Coverage Coverage Ceiling Coverage Coverage Height Diameter Area Height Diameter Area 8 ft 7 7 ft 46 ft 2 5m 2 6m 5 1 m 10 ft 12 8 ft 129 ft 3 0 m 3 8 m 11 6 m 12 ft 17 9 ft 252 ft 3 5m 51m 20 6 m 14 ft 23 0 ft 417 ft 4 0m 6 4m 32 2 m 16 ft 28 2 ft 623 ft 45m 7 7m 46 3 m 18 ft 33 3 ft 870 ft 5 0m 9 0m 63 0 m 20 ft 38 4 ft 1158 ft 5 5m 10 2m 82 3 m 6 0m 11 5 m 104 2 m
3. 0 55 0 50 STI 0 60 0 55 0 50 ALcons 6 6 8 7 11 4 POOR BAD CIS 0 65 0 60 0 54 0 47 0 39 0 29 0 16 0 00 0 00 0 00 RASTI 0 45 0 40 0 35 0 30 0 25 0 20 0 15 0 10 0 05 0 00 STI 0 45 0 40 0 35 0 30 0 25 0 20 0 15 0 10 0 05 0 00 ALcons 14 9 19 5 25 6 33 6 44 0 57 7 75 7 100 100 100 Continued on next page 3 6 Measures of Intelligibility Continued The STI Method STlpa STITEL RASTI Percent ALcons Phonetically Balanced Word Scores 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 These 98 measurement points 7 x 14 are weighted and combined to create a number between 0 0 totally unintelligible and 1 0 perfectly intelligible The standardization of the carriers and modulation frequencies to be used as well as the weighting to be applied has now been standardized by IEC 60268 16 The STI method is the most accurate of all intelligibility measures however the procedure can take as long as 20 minutes per test Alternate methods such as STIpa
4. Audio engineers use Decibels dB to express ratios between levels 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 P and Po Decibel 10 log 2 Po Equation 2 1 The Decibel Pois the reference power and P 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 in SPL You can also use the decibel for voltage comparisons From Ohm s Law we know that V x R Where V Volts I Amps R Resistance Equation 2 2 Ohm s Law The electrical power equation Equation 2 3 Power Relationships Use the following equation to determine the decibel difference between two voltage measurements powering the same load resistance v Y gt dB 10 log R z Which can be simplified to dB 20log Vo Vo Equation 2 4 dB and Voltages The decibel is often used to make comparisons between two different numbers neither of which is at an absolute reference level For instance if we take two voltage measurements along the length of a speaker circuit the power lost to the wiring can be calculated directly
5. The answer invariably is that depends There are many layout patterns to choose from each suitable for different room geometries background noise and reverberation times See Table 2 2 Layout Pattern Selection Guide for some recommendations The most common layout pattern is the rectangular pattern shown in Figure 2 7 below Table 2 2 Layout Pattern Selection Guide Pattern Description 2x Edge to Edge 1 4x Edge to Edge rooms with low noise and low reverberation Edge to Edge Preferred layout pattern for most areas Minimum Use with areas of high reverberation Overlap and or high ceilings For the worst areas generally provides excellent intelligibility for even difficult areas Use with caution this type of Full Overlap pattern can result in lower than expected intelligibility due to multiple speaker interaction Modeling is recommended for areas that would need this layout pattern Table 2 3 SPL Variation by Layout Pattern Not recommended except for tone only signaling or small rooms with low noise and low reverberation Uses fewer speakers than Edge to Edge pattern Only appropriate for Speaker layout patterns rectangular placement ao Y ee OJO 1 4x Edge to Edge 2 2x Edge to Edge Increase in SPL penado Speaker Layout Over Single Variation in Edge to Edge Minimum Overlap Full Overlap Pattern Coverage Speaker Standar
6. tyco Safety Products Fire Alarm Audio Applications Guide Guideline for Designing Emergency Voice 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 Copyrights and Trademarks Copyrights Trademarks Notice Copyright 2005 Tyco Safety Products Westminster All rights reserved All specifications and other information shown were current as of document revision date and are subject to change without notice Printed in the United States of America Tyco Simplex and the Simplex logo are trademarks of Tyco International Services AG or its affiliates in the U S and or other countries All other products are trademarks of their respective manufacturers All registered and unregistered trademarks are the sole property of their respective companies This guide is intended as an informational resource and is not intended to provide definitive legal engineering design or architectural advice Legal engineering design or architectural requirements and interpretations may vary from jurisdiction to jurisdiction or project to project Therefore no warranty or representation is made about the sufficiency of any of the contents of this guide Tyco Safety Products Westminster
7. INTFOQUCION eiee daniela acs eetie other 3 2 Background NOISE iia aa asia E E 3 3 Reverberation csm tasar anda naa 3 4 Distortion aiii dati ar 3 5 Microphone Technique eiii 3 5 Measures of Intelligibility oooonnnnccnnnnniccnnnnncconnanccccnnnarcccnnnoncccnnnrrc cnn nan rcc naar nncncnnn 3 6 INTO AUCTION cacon a dd E 3 6 The Common Intelligibility Scale CIS oooooonnnnninicicnna naciona nacinnnanacananar rara 3 6 The STIMethod iii Etc 3 7 RN ae 3 7 STE A a A a 3 7 RAS Ti A AA A Aa A Ei 3 7 Percent ALCOnS 2 A Sn eae 3 7 Phonetically Balanced Word Scores 0 ocoonnocccconnccccccononccccanoncncnan cnn cnn nn nr nana rca 3 7 Practical Measurement of Intelligibility oo ooonnnnnicnnnnncconnnncccnnnanccccnn anna narccnnnno 3 8 INTOQUCUION citadino idas A E T E T AO 3 8 Tools for Predicting Intelligibility e rece nn A a A 3 9 IMtPODUCHON eosi di dad 3 9 Acoustical Modeling Software oooonnnocinnnicocinnnococnnonononcnn nono na nn nano nn nr rnnn nn rro rca 3 9 Chapter 4 Emergency Voice Alarm Communications Systems 4 1 INTOdUCHON cion ais 4 1 inthis Chapter ama noob 4 1 A Typical Emergency Voice Alarm Communications System ooooncccninnocicnananccnnnnnanos 4 2 Parts of an Emergency Voice Alarm Communications System 0 ccceseereeeeee 4 3 Command Cemer tic vs scree acini lt e eae 4 3 AUGIO A 4 3 Transponder sagnia neers eed aaa eee eA 4 3 Speaker Circuits iii a A did 4 4 Chapter 5 Regulatory Issues
8. In this Chapter Refer to the page number listed in this table for information on a specific topic Topic See Page Influences and Intelligibility 3 2 Measures of Intelligibility 3 6 Practical Measurement of Intelligibility 3 8 Tools for Predicting Intelligibility 3 9 3 1 Influences on Intelligibility Introduction The figure below lists the relative contributions of each frequency band Octave Band Contribution to Intelligibility 35 30 25 20 15 10 5 Relative Contribution to intelligibility 0 125 250 500 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 There are many factors that affect the intelligibility of messages presented over public address systems in public and private spaces Some major intelligibility factors include e Background noise e The configuration of the space being addressed e The acoustical properties of the materials on the walls floors and ceilings e The distortion and bandwidth of the sound equipment e The characteristics of the person speaking male female accent microphone technique etc S
9. SPL distribution information reverberation time results and speaker coverage information are also available AC iTool 579 769 Examples iTool File Edit Options Help 2 C XiToo11579 769 Examples iTool File Edit Options Help 0009009090000 00000000900 F 7 ts i E Cs sults Q Poet RoomData Speaker Location S rib Reverberation Time O Project Room Data Speaker Location SPL Distribution Reverberation Time 8 coRRIDOR Resolution Low J High X 176Feet Y 1 Feet SPL 84 4 dB coprivor Loser nese Loser Room Width 54 Feet orrice we orrice Room Length 340 Feet gt 100 Room Height 10 Speakers Required 100 Speaker Tap Setting 025 Total Power Required 25 of Columns X of Rows Y First Speaker X Coord First Speaker Y Coord Room Length 340 Feet Column Spacing Row Spacing 30 88 86 84 82 80 78 76 74 72 70 68 66 64 62 60 58 56 gt 50 gt 40 gt 30 lt 30 Figure 6 3 Office Space SPL Distribution Figure 6 4 Office Space Reverberation Time Results and Coverage Information Continued on next page 6 5 Applying the Methods Continued Example 2 Corridor In this example consider a standard office corridor with the following specifications e Dimensions 100 Lx 12 W x10 H e Flooring Tile e Ceiling Acoustic Tile e Walls Gypsum over 2 x 4
10. STITEL and RASTI described below are subsets of the STI method with faster measurement times This is a special adaptation of the STI method for the measurement of speech intelligibility for public address PA systems It is a modification to the STI method that has been correlated to within 0 03 CIS of a full STI measurement The STIpa method is implemented in the Simplex GoldLine intelligibility measurement system The STITEL method is a special adaptation of the STI method used for the measurement of speech intelligibility for telephone systems It reduces the 14 modulation frequencies to seven and applies one to each of the seven octave bands simultaneously The Rapid Acoustics Speech Transmission Index RASTI is a simplified version of the STI method that uses two octave bands instead of seven with four modulation frequencies measured in one band and five in the other for a total of nine measurements The Articulation Loss of Consonants ALcons is a measurement method for speech intelligibility that is based upon the importance of consonant sounds in the overall perception of speech It uses specially chosen simple words in transmission tests ALcons is expressed in percent ALcons This is a subjective test with a much greater potential for variations in score than some of the other tests described The Phonetically Balance PB word score is described in ISO TR 4870 and consists of specially chosen words
11. did not take into account ongoing changes in the construction of the building the construction materials used in a 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 properly 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 help design a system that meets the requirements for speech audibility and intelligibility in a cost effective manner This guide is separated into the following chapters e Chapter 1 Speech Intelligibility Overview Provides an overview of audio intelligibility and an introduction to the topics covered in this publication e 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 e Chapter 3 Speech Intelligibility Details the influences and measurements of intelligibility e Chapter 4 Emergency Voice Alarm Communication Systems Details emergency voice alarm communicatio
12. 5 1 Introductio atrasa it 5 1 INthiS GONApter str tn n ee 5 1 AUIDILILY coi AA eee eee 5 2 Tones and SPL cnc ihinnetcnaienite ias 5 2 High Background NoiSB oooooccccocooccccconocnccccononcncnanoncncnnno cnn c nano nn nr nano rn rra rra rra 5 3 Large AIS A A Miata balan aie tet 5 3 lintelliGibilityis a a Rae tad altos ah ern gece Raa 5 4 Intelligibllity gt 0 ataca 5 4 Intelligibility Certification eeina EEE OE TE rar rr 5 5 Chapter 6 Speaker System Design Method 6 1 INTOdUCION neran Ady health a intl de 6 1 Inthis Ghapter it e ete lath ted ea 6 1 Speaker Design Method orere di id 6 2 A ii areetan at ud deeded di dndev aaae ia tt e E iaeia 6 2 Step 1 Room CharacteriStiCS vecinita Mens aahicstedegtebba a a aaae aaa 6 2 Step 2 Calculate the Number of Speaker ooococcccccccocococococccccccnnonnoncnncnnnnnannn monos 6 2 Step 3 Audio Power and Individual Speaker Wattage Tap cceeeeeeees 6 2 Step 4 Model Design to Predict Intelligibility oooonnnnnninnnncconnnncconnanncccnnnno 6 2 Step 5 Verify Final instalation ienesa aa RA 6 2 Recommendations for Maximizing System Intelligibility ooonnnnnnnnnnnnnn ccn n 6 3 Maximizing Intelligibility oooonnnnicnnnnnnicnn nnoconnnncccnnnacrcccnnnarnnr cana rra rra rar 6 3 Applying the Methods y a indi eee 6 4 Design Examples enaa eeete tte it a E AAA 6 4 Example 12 Office Space iman ne ieee een ets tae 6 4 Example 2 Comidor cita Dan
13. DER SPL 05 18 Legend cB on 2100 EEES QREBRVSHLRRSNeaASBSERSS E Figure 6 17 Lobby SPL Distribution Continued on next page 6 11 Applying the Methods Continued Example 4 The following screen shows the reverberation time and speaker coverage information Lobby continued C iTool 579 769 Examples iTool File Edit Options Help Ceeeeeeeee rs 6 Project Room Data Speaker Location SPL Distribution CORRIDOR r Reverberation Time Results LOBBY Frequency 125Hz 250Hz 500Hz 1 KHz 2 KHz 4 KHz OFFICE Reverberation Time 06 o7 o9 o8 f 07 J 04 Intelligibility Weighted Average Reverberation Time 0 6 Average Reverberation Time 0 7 Coverage Info EdB down coverage circle diameter listener plane 128 Layout circle diameter based on selected layout pattern 128 Maximum listener SPL Alarm notification and noise combined 855 Maximum SPL 855 Minimum SPL Tea SPL variation over listening area 44 Figure 6 18 Lobby Reverberation Time and Speaker Coverage Information 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 presente
14. Feet 5 GYM Room Height Feet Speakers Required Speaker Tap Setting Total Power Required of Columns gt lt of Rows Y First Speaker X Coord First Speaker Y Coord Column Spacing Row Spacing Room Length 80 Feet Figure 6 10 Gymnasium Speaker Location Guide SPL distribution information reverberation time results and speaker coverage information are also available Al C XiTooI1579 769 Examples iTool DEAR Al C XiTooI1579 769 Examples iTool Eile Edit Options Help Eile Edit Options Help 000000900900 0000000008 Calculation has finished You may click on the tabs below to review results i a Q Pojet Room Data Speaker Location Reverberation Time Q Pojet Room Data coRRDoR Resolution Low J High X 79Feet Y 152Fest SPL 74 3 dB CORRIDOR y Revetberation Time Results FSSRLASSINPASSRLRBGS Lossy lees Losy Frequency 125H2 250Hz S00Hz 1KHz 2KH2 6 DFFICE a OFFICE Reverberation Time 78 46 62 75 54 a GYM 0 O GYM Inteligibilty Weighted Average Reverberation Time 52 Average Reverberation Time Coverage Info EdB down coverage circle diameter listener plane Layout circle diameter based on selected layout pattern Maximum listener SPL Alarm notification and noise combined j Maximum SPL Minimum SPL Par SPL variation over listening area gt 50 Figure 6 11 Gymnasium SPL Distribution Figure 6 12 Gymnasium Reverberation Time Results and C
15. Reference Manual JBL Professional Northbridge CA Sound Systems for Emergency Purposes International Electrotechnical Commission IEC 60849 1998 02 Sound System Engineering by Don amp Carolyn Davis published by Howard Sams amp Co Tyco Safety Products publications STI CIS System Users Guide 579 377 iTool Installation and User s Guide 579 772 vi Introduction Chapters of this Publication In this Chapter Chapter 1 Speech Intelligibility Overview 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 reductions 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 been gaining momentum throughout the fire alarm industry NFPA 72 the National Fire Alarm Code now requires that emergency voice alarm communications systems be 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
16. allowed by NFPA 72 is 110 dB lower in some jurisdictions and is clearly an excessively loud system possible hearing damage could result In these cases visual notification would be preferred with speakers located in areas away from the noise sources in areas designated for evacuation message broadcast Reverberation is the effect of sound being reflected off of surfaces from many different directions Unlike echoes which are a distinct reflection of the sound reverberation is essentially the effect of many small echoes Note See Chapter 2 for more information on reverberation Because reverberation contains portions of the original speech delayed from the original source the reverberant sound becomes noise interfering with intelligibility Reverberation has a smearing effect on the sound that the listener hears as shown in the figure below The speech modulations are reduced by sounds arriving after the original sound Notice that the valleys of the modulations are now filled with the reflected sounds reducing the overall modulations Figure 3 4 The Speech Pattern An Emergency Has Been Reported with Reverberation Reverberation times typically range from less than 400 ms for typical office spaces with carpeting and cubicles to several seconds for gymnasiums and auditoriums In general rooms with reverberation times higher than 1 5 seconds must be designed using professional analysis and modeling Note Chapter 6 provides e
17. attained from the iTool e The iTool reverberation time calculator estimates a reasonable T60 time of 0 62 seconds e Using an Edge to Edge pattern the resulting total number of speakers is 4 tapped at 0 25 W for a total of 1 W of audio power required Continued on next page Applying the Methods Continued Example 4 Lobby continued AN C iTo01 579 769 Examplos Too tp 0000000000 FF Figure 6 16 Lobby Speaker Location Guide The existing design had two wall mounted speakers to the left and right of the entrance doors Stairwell Command Center N Reception Desk Figure 6 15 Lobby Layout The following screens below show the lobby speaker location guide and the SPL distribution for the lobby Calodahon has Ireshed You may click on the Labs below to even resus Room Width Room Length Room Height N Speakers Required Speaker Tap Setting Total Power Respisnd of Cokes DO Rol Rows 1 Fact Speaker X Coed Fast Speaker Y Coord Column Spacing Row Spaong 057 fos E Fen Ci ree EJ 135 wa Iv C2 l CE Feet ED Feet OZ Feet E Few Y Ficom Length 2d Feet IGI C MTo01579 769 Examples iTool Ele E Options Heip 0000000000 F Calodahon has Ireshed You may chok on the labs below to review results Room Dales Speaker Locaton SPL Distribution Rewerberatices Tano Resohion Low gt a Ya 13 Feet
18. 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 The screens in this publication were current at the time of print The iTool software interface may appear slightly different on your system A common system design involves office space These spaces are typically benign acoustically with low reverberation times and low background noise levels Consider a large office area with the following specifications e Dimensions 340 Lx 54 W x10 H e Flooring Carpeted Floor Over Concrete e Ceiling Acoustic Tile e Walls Gypsum over 2 x 4 16 on center and 0 375 Plywood Paneling e Ambient Noise 55 dB Typical background noise for an office setting This information is entered into the iTool 2 C iToo14579 769 Examples iTool File Edit Options Help 0 00 e e e a ee Unit Pe y fini 4 Project RoomData Speaker Location SPL Distribution Reverberation Time CORRIDOR Room Length Width Height Loser Dimension 340 54 To Feet Omm Floor Carpet Medium Pile on Concrete Ceiling Tectum 1 5 Acoustic Ceiling Tile Wall 1 Plywood Paneling 0 375 Wall 2 Gypsum over 2 x 4 16 o c Wall 3 Plywood Paneling 0 375 Reverberation Time Wall4 Plywood Paneling 0 375 Required Speakers Speaker Truealert ceilin
19. 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 The drop in SPL is referred to as the Inverse Square Law and originates from the fact that as the diameter of the sound sphere doubles the surface area increases by a factor of four This behavior of outwardly radiating sound causes a drop in SPL of 6 dB per doubling of distance You can calculate the change in SPL at any distance from a speaker as follows g N A dBx 20 D spl og gt D SL ad 1 l l 1 Equation 2 8 The Inverse Square Law The figure below illustrates how SPL decreases with distance as you move away from a speaker Source 93dB 10 reference location dB and Distance Chart 93 90 84 dB 81 78 69 20 40 60 80 100 120 140 160 Distance from source Figure 2 3 dB and Distance Chart Continued on next page 2 9 Speaker Basics Continued Sensitivity Speaker Dispersion Angle and Q The amount of sound that a speaker can be expected to produce is found in the speaker s sensitivity rating provided in the manufacturer s literature Sensitivity is the amount of sound 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
20. placement in the structure play a major role in determining how many devices are necessary for adequate intelligibility The numerical count of devices for a given design and protected space cannot by itself be used to determine the adequacy of the design Sometimes the acoustic problems of certain placement constraints can be satisfactorily overcome through the careful selection of loudspeakers with the requisite performance characteristics rather than by increasing their number There might be applications where not all spaces will require intelligible voice signaling For example in a residential occupancy such as an apartment the authority having jurisdiction and the designer might agree to a system that achieves the required audibility throughout the apartment but does not result in intelligible voice signaling in the bedrooms The system would be sufficient to awaken and alert However intelligibility might not be achieved in the bedrooms with the doors closed and the sounder in the adjacent hallway or room In some cases this can require that messages repeat a sufficient number of times to ensure that occupants can reach a location where the system is sufficiently intelligible to be understood Systems that use tone signaling in some areas and voice signaling in other areas would not require voice intelligibility in those areas only covered by the tone Reverberation times can drop significantly with the presence of plants furnit
21. selected from a known population transmitted to a panel of listeners This is a subjective test with a much greater potential for variations in score than some of the other tests described 3 7 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 One of these is the STI CIS meter available from SimplexGrinnell The meter uses the STIpa method to provide a fast and easy measurement of total system speech intelligibility It measures both intelligibility and audibility as it also has a built in dB meter The meter automatically converts the STIpa measurement to CIS so that demonstrating that a system meets the requirements of NFPA 72 is easy and intuitive A proprietary test tone is played through the system which the analyzer uses to determine reduction in speech modulation STI CIS Analyzer Talkbox A Speaker Microphone Holder STlpa Test Tone CD AC Adapter if Volume Control Figure 3 5 STI CIS Intelligibility Measurement System 3 8 Tools for Predicting Intelligibility Introduction Acoustical Modeling Software Several tools varying in levels of complexity
22. the sensitivity is rated at 1 W of power and 10 feet 3 meters from the speaker By knowing the speaker s sensitivity you can determine the on axis SPL SPL measurements taken directly in line with the speaker at any distance from the speaker using the following equation Where e SPL Sound Pressure Level MNG Dr D Distance from the speaker SPL Sensitivity 20 log D Dr The reference distance Sensitivity The SPL at the reference distance Equation 2 9 On Axis SPL Calculation Simplex speakers have two sensitivity ratings listed on their respective data sheets a reverberant chamber test as required by UL Standard 1480 and an anechoic rating as defined by ULC S541 The reverberant chamber specification is derived from a test where the speaker s sound is emitted in a chamber specifically designed to reflect all of the sound so that a total sound power measurement can be made Correlating the speaker s reverberant chamber sensitivity rating with real world acoustics has proven to be difficult Typically the anechoic rating at 1 kHz is more representative of real world performance The speaker sensitivity rating while useful for comparing speaker models tends to oversimplify the true response of a speaker Speakers beam sounds analogous to the way a flashlight produces light the beam of sound is loudest directly in line with the device and becomes quieter the farther the listener moves away from the center
23. to change a distributed overhead system or a combination wall mount and overhead design should be considered This minimizes the variation of audibility and intelligibility e Jn rooms with low hard ceilings the sound emitting from the top hemisphere of the coverage pattern is reflected off the ceiling and down to the listener This can increase the reverberant field sound level and result in delayed arrival of sound These factors both contribute to a reduction in intelligibility Continued on next page Distributed Wall Mounted Systems Continued Design ofa 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 Therefore the audibility calculations must be done with the listener at the farthest distance from the speaker In a room with speakers mounted along a single wall the farthest distance lowest SPL can be taken within 3 feet 1 meter of the opposing wall In general the wall mount speakers are located between 80 and 96 inches above the floor This satisfies the requirements for speaker strobe combination units The figure below shows the typical coverage of a wall mount speaker Simplex Wall Mount Speaker Viewed from ceiling Coverage Example vall ES OSE SESOSONSONESE SOS ES ES OE KA Room Depth Critical Polar Angle On Axi
24. to measure and quantify the transmission quality of speech with respect to intelligibility These methods are used for rating intelligibility and take into account room acoustics as well as the various components of the sound system The intelligibility ratings derived by these methods can then be used to compare speech transmission quality at different positions within one room or for different conditions within a space IEC 60849 Second Edition 1998 states that a minimum intelligibility level of 0 7 on the Common Intelligibility Scale CIS must be met in all areas that require an emergency voice alarm communications system NFPA 72 references IEC 60849 and a CIS score of 0 70 as the preferred method of determining intelligibility This makes understanding the CIS important to understanding measurements of intelligibility The CIS is not a method of measuring intelligibility itself but is a standardized scale to which a variety of measurement methods are correlated This allows a number of different measurement techniques to be used with a common baseline to which they can be compared Each of the test methods described in the following sections has been correlated to the CIS and can be used to determine a CIS rating The correlation between the CIS STI and CIS ALcons measurement methods is provided in the following figure Table 3 1 Correlation of CIS and with STI and ALcons FAIR CIS 0 78 0 74 0 70 RASTI 0 60
25. 000 Fa 9 Project Room Data Speaker Location SPL Distribution Reverberation Time 8 corripor Loser Room Width iz Feet OFFICE Room Length 100 Feet GYM Room Height 10 Feet Cras cot Speakers Required 5 Speaker Tap Setting 0 25 Watt Total Power Required 12 Watt of Columns lt 5 of Rows Y 1 First Speaker X Coord 10 Feet gt e First Speaker Y Coord D Feet lt 20 gt Room Le gth 100 F et Column Spacing 20 Feet Row Spacing 0 Feet Figure 6 6 Corridor Speaker Location Guide SPL distribution information reverberation time results and speaker coverage information are also available Average Revesbouation Tine Oe TG c uToar 579 759 Examples JToal BICA Toan 579 769 Examples iToal A Eje gk gns eip Eje gk gions peip 0000000000 ra 000600060000 r O Popa RoomDala Speaker Locaton SPL Damuso Reverberston Tine O Prorat Room Dala Spesker Locaton SPL Distibuton Reveeraioni Tane CORRIDOR Resolu or Low Ji Beti X I Fee Ya 2Feet SPL 01 d CORRIDOR p Flevesberation Tine Nens Looby Looby Frequency Whe 250 He 500 Ha TEHe 2 KH AKH ames Legend 08 omte Reveiberaton Tine aa 08712 1 171007 104 6 em 5 em Irbeazidly Wengthed Average Heveiberaton Tine 07 30 l r Coverage leo 64D doum coverage cicle diameter linener plane CA Feet Layout cache durneter haced on eninctad layout pathan OIT Feet Maximum listener
26. 16 on center e Ambient Noise 60 dB E C riTool 579 769 Examples iTool File Edit Options Help 00660606GGBGBBGA Fa 4 Project Speaker Location SPL Distribution Reverberation Time 8 CORRIDOR Room Length With Height Loey Dimension 700 72 10 Feet orice z gt pl o ata ede Ceiling Tectum 1 Acoustic Ceiling Tile wall Gypsumover2e4 16 0c wal2 Gypsumover2x 4 16 0 0 Wall 3 Gypsum over 2x 4 16 0 6 Reverberation Time ES Wall 4 Gypsum over 2 x 4 16 o c Required Speakers Speaker Truedlert Wall Mount Speaker w Speaker wattage Placement Edge to Edge Total Audio Power Spacing Listener Height Ls Feet Ambient Noise 5 Required Signal to Noise Ratio 15 dB Figure 6 5 Corridor Design Example The following basic results are attained from the iTool e The iTool reverberation time calculator estimates a reasonable T60 time of 0 7 seconds e Using wall mount speakers in an Edge to Edge pattern the resulting total number of speakers is 5 tapped at 0 25 W for a total of 1 25 W of audio power required Continued on next page 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 E C viTool 579 769 Examples iTool File Edit Options Help 0000660
27. If the voltage at the amplifier driving a speaker circuit is 25 V Vo and the voltage at the last speaker on the circuit is 15 V V1 the power loss due to the wiring is 4 4 dB Continued on next page 2 2 Basic Audio Math Continued Ohm s Law and the Decibel continued reference SPL When the decibel is used to express SPL the reference sound pressure is 20 x 10 Newtons m which is approximately the threshold for hearing for a normal listener When using a dB meter to measure sound the meter is performing the calculation between the received SPL and the SPL 20x10 dB 20log Equation 2 5 dB and Sound Pressure Levels Adding Decibels add decibels directly When multiple sound sources are combined there is an increase in SPL However you cannot 90 dB 90 dB is not 180 dB but 93 dB Doubling the power results in a 3 dB SPL increase To add SPL decibels 1 Convert the decibels back to the original power value which for SPL is referenced to 1pW or 10 W 2 3 To add 90 dB 90 dB Add the numbers together Convert the numbers back to decibels i dB 10 log E Po 1 pW 10 2 W P P go P pg rele 1072 P la 0 1 072 la 03 0 001 W 2P 2 x 0 001 W 0 002 W 9 109 1 dB 10 log Sor 93 Equation 2 6 Adding Decibels 2 3 Sound and Hearing The Relationship Between Sound and Hearing Sound is created by mechanical vibr
28. SPL Alam notification and noise combined BR BD Marim SPL oT e Minimum SPL m sa SPL variation over ltering areo MT a Figure 6 7 Corridor SPL Distribution Figure 6 8 Corridor Reverberation Time Results and Coverage Information Continued on next page 6 7 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 In addition the background noise is highly dependent on the use of the gym if there is an audience the noise level can get very high Consider this gymnasium example with the following specifications e Dimensions 80 Lx 160 W x 20 H e Flooring Wood e Ceiling Gypsum e Walls Gypsum e Ambient Noise 50 dB This information is entered into the iTool 2 C iTool1579 769 Examples iTool File Edit Options Help m eeeeeceeeee rF 6 Project Room Data Speaker Location SPL Distribution Reverberation Time CORRIDOR poom Length Width Height Losey Dimension gg 160 20 Feet orice z loor O GYM wood Parquet Floor Ceiling Gypsum over 2 x 4 16 o c Wall 1 Gypsum over 2 x 4 16 o c wall 2 Gypsum over 2 x 4 16 o c Wa
29. This beaming effect is also dependent on the frequency of the signal The beaming effect is referred to as the directivity or polar response of the speaker and is occasionally provided by manufacturers in the form of polar plots For typical fire alarm speakers the beam is very wide for low frequencies low directivity and becomes more focused for higher frequencies When determining coverage area it is common practice to use the directivity information at 2 kHz a critical band for intelligibility Fire alarm speakers produce the highest output in the 800Hz to 4 kHz frequency range Continued on next page 2 10 Speaker Basics Continued Speaker Dispersion The figure below includes a typical polar plot graph and the interpretation of the dispersion angle Angle and Q continued Simplex 4902 9721 Ceiling Mount Speaker Polar Plot 2kHz 0 6dB division Note See Figure 2 5 on the following page for a more detailed way de view SN WO a ESO S RUZ pid Dispersion Angle Sensitivity 93dB 10 Feet 1 W Figure 2 4 Speaker Polar Plot Interpretation The Coverage Angle is defined as the angle where the speaker SPL drops 6 dB from the on axis 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
30. and communicates status back to the command center There is typically one transponder for every three floors in a high rise building Voice paging equipment included in a transponder is e Audio Riser Interface Modules Receives the riser for distribution to the amplifiers and includes protection and isolation components e Amplifiers Amplifies the audio signal to produce 25 V or 70 7 Vrms for distribution to the NACs e NACs Notification Appliance Circuits Distribution points to the speaker circuits provides electrical supervision of opens shorts and Earth faults of the field wiring The speaker routing switches at the command center are used to selectively turn the NACs on Continued on next page 4 3 Parts of an Emergency Voice Alarm Communications System Continued Speaker Circuits Speaker circuits convert electrical power from amplifiers into sound These circuits are wired in a daisy chain fashion with a single path of electrical continuity from the NAC to the last speaker in the circuit The speaker circuits can be wired in Class A or Class B configurations Class A operation allows the circuit to operate through a single Open while Class B circuits only detect the Open Neither circuit operates through a Short Circuit condition but either can report the trouble Note Speaker circuits are normally supervised with DC voltage during the standby or non alarm state when the speaker circuits are OFF To use speaker
31. angle is 120 degrees Listener we 6dB edge of Height coverage area Figure 2 6 Maximum Theoretical Coverage Angle Continued on next page Speaker Basics Continued Speaker Coverage continued Determining Critical Polar Angle Real world speakers have some polar loss at angles less than the rated dispersion angle In order 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 For example consider the Simplex 4902 series speakers The dB loss as a function of angle off axis can be determined from the polar plot as illustrated in figure 2 7 below Because this speaker has symmetrical dispersion only the data from one quadrant is required Adding the polar losses and distance losses yields the total loss for the speaker along the listener plane Inspecting the total loss data reveals that the critical angle is between 40 and 50 degrees Using the spreadsheet s forecast function pinpoints the angle at which the SPL drops 6dB as 51degrees Because of symmetry this angle is doubled to end up with a critical polar angle of 102 degrees 0 10 20 30 40 50 Angle Of Axis 8 o 10 20 30 4 50 oO Polar Loss 1 0 0 dB 0 0 dB 0 1 dB 0 5 dB 1 3 dB 1 8 dB 3 0 dB Distance Loss 2
32. ations that displace air molecules to create repetitive changes in air pressure The ear detects these changes in air pressure with the magnitude of the pressure perceived as loudness and the frequency of the changes perceived as pitch Due to the physiology of the ear sound pressure does not correlate directly to the perceived loudness over all SPL and frequencies The ear is most sensitive to frequencies between 3 to 5 kHz and much less sensitive to low frequencies For a low frequency tone to be perceived as loud as a high frequency sound it must have a much higher SPL In addition the ear s sensitivity to the low frequencies also depends on the SPL At high sound volumes the loudness difference between the most sensitive frequencies and low frequencies is reduced q LOUDNESS The non linear nature of the ear s 120 SS ln O LEVEL PHON response to frequencies and loudness is well documented in the Fletcher Munson equal loudness curves updated in the Robinson and Dadson equal loudness curves that were adopted in the ISO International Standards Organization Recommendation R 226 JJ 8 60 40 Note The MAF Curve in Figure 2 1 represents the Minimum Audible Field Curve 20 SOUND PRESSURE LEVEL IN dB RE 20 Nim 20 100 1000 5000 10 000 FREQUENCY IN Hz Figure 2 1 Robinson and Dadson Equal Loudn
33. be increased 10 fold 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 Amplitude modulations of speech patterns are seen as the peaks and valleys of the waveform These modulations range from 0 63 Hz to 12 5 Hz A typical fragment of speech an emergency has been reported is shown in the figure below An emergency has been reported Mh TT AY Figure 2 2 Speech Pattern that Illustrates Modulations Consonants Consonants generally have the lowest power contribution to speech but are extremely important and Vowels to intelligibility Consonants like the T and S sounds are relatively high in frequency but of a short duration Vowels A E I O U sounds carry most of the power of the speech signal 2 5 Room Acoustics Introduction Reverberation This section is provided as a summary of room acoustics See the references in the Related Documentation section earlier in this manual for a list of publications containing more thorough discussions of this subject Reverberation is one of the most important contributors to reduced intelligibility and is the result of sound being reflected off floors wa
34. can assist the sound system designer in producing a system of acceptable intelligibility These range from simple layout guides for speaker placement to complex computer modeling tools which can accurately simulate and predict sound system performance in complex spaces These tools also have the ability to listen to simulations of system performances at any location within the space The tools selected should be based on the complexity and characteristics of the particular installation In many cases layout guides and rules of thumb are adequate to produce an effective design In other cases sophisticated modeling and analysis is necessary There are a number of computer modeling and simulation tools available to the sound system designer that provides reliable predictions of speech intelligibility and audio coverage throughout the modeled space These tools can help the designer through difficult situations or in designing emergency voice alarm communications system for spaces with complex audio environments The best known and widely used of these modeling programs is EASE from Renkus Heinz Another program is Modeler available from Bose Corporation Both of these programs have shown good correlation between predicted results and actual measurements when the system is modeled accurately These programs provide a reliable means to confidently design and build more complicated systems that require minimum speech intelligibili
35. circuits for non alarm paging or background music applications you must have approval of the AHJ Authority Having Jurisdiction Specially designed hardware is available to supervise speaker circuits when used for non alarm content 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 OWN V Sselg Class B Wiring End of Line Resistor OWN 4 Ssejo Figure 4 2 Class A and B Speaker Circuit Wiring Introduction A In this Chapter Chapter 5 Regulatory Issues 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 Some key specifications for the design of speaker systems are found in the Notification Appliances for Fire Alarm Systems chapter of NFPA 72 IMPORTANT This chapter contains excerpts of NFPA 72 2002 National Fire Alarm Code Always verify which version of the code is enforced locally Refer to the page number listed in this table for information on a specific topic See Page Audibility 5 2 Intelligib
36. d a summary of those considerations in order to better understand the concept of speech intelligibility If an area is quite large or is expected to have significant reverberation characteristics or has other complicating influences such as high ambient noise speaker selection and placement will require sophisticated modeling tools to determine the equipment needed for proper speech intelligibility However if the areas of concern are easily defined are relatively small and are expected to provide minimal reverberation the methods described in this guide provide a good reference toward understanding proper speaker selection and placement Contact your local SimplexGrinnell representative for additional information concerning the STI CIS Analyzer and for information about the Simplex line of Emergency Voice Alarm Communications Systems 6 13 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 7 2 7 1 Glossary Glossary or Terms This list provides brief descriptions of various terms relating to this publication ABSORPTION COEFFICIENT The ratio of absorbed to reflected sound The absorption coefficient has a range of 0 to 1 A WEIGHTED DECIBEL The ear is less sensitive to low frequency pitch at low vol
37. d layout 2x Edge to Edge 0 2 dB 10 4 dB 1 4x Edge to Edge Gag a Figure 2 7 Speaker Layout Patterns Edge to Edge 0 7 dB 4 4 dB Minimum Overlap 2 0dB 2 0 dB Full Overlap 5 2 dB 1 4 dB 2 15 Distributed Wall Mounted Systems Introduction Advantages Disadvantages 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 Advantages and disadvantages of distributed wall mount systems are described in the following sections e For narrow areas such as hallways fewer speakers and less amplifier power may be needed to cover the same size area This is because all of the speaker s sound contributes to useable audibility e Mounting can be on more than one wall This further improves the distribution of direct sound to the listener e Wall mounted speakers put sound directly into the listener area This can reduce the excitation of the reverberant field e Combination speaker strobe units permit voice and visual notification in a single appliance e The sound field from wall mount speakers is more likely to encounter obstructions from furnishings such as cubicle walls in office environments or movable partitions in conference rooms If the furnishings in a room are likely
38. d phrases may be preferred These messages provide a consistent sound level output and a controlled speech pattern and pace that may be more intelligible than an unpracticed announcement via microphone 3 5 Measures of Intelligibility Introduction The Common Intelligibility Scale CIS 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 What is intelligible to one person may not be intelligible to another Some people have hearing problems that render it difficult for them to understand what others easily understand Some people talk more quickly than others or with an accent so that they may not be understandable in environments in which other speakers are easily understood In an effort to create quantifiable measures of intelligibility the test methods take the subjective elements the talker and the listener out of consideration It is assumed that the speaker has an average tone of voice and speaks at a normal speed It is also assumed that the listener has average hearing and is fluent in the language being spoken If either the speaker or listener deviates from the average the intelligibility of the communications is affected Several methods have been developed
39. dB the intelligibility of speech actually decreases with increasing volume This implies that areas with background noise greater than 80 to 90 dB can pose a challenge to the system designer Continued on next page 3 3 Influences on Intelligibility Continued Background Noise continued Reverberation Some types of background noise have a greater impact on intelligibility than others depending on 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 HVAC noise tends to have most of its energy concentrated in one or two octave bands in the lower frequency range which has a lesser contribution to speech intelligibility than mid bands NFPA 72 recognizes this fact and states In areas where background noise is generated by machinery and is fairly constant a frequency analysis can be warranted Note See Chapter 5 Regulatory Issues of this manual for more NFPA Codes and Guidelines There are limits to how much sound can be produced to overcome background noise Take the case of a manufacturing area with 90 dB average background noise To overcome the noise the speaker must produce 105 dB at the listener and could exceed 120 dB near the speaker depending how far the speaker is from the listener The maximum SPL
40. 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 Readers with specific questions should consult the appropriate advisor Table of Contents Chapter 1 Speech Intelligibility Overview 1 1 IMFO GUCUIOMN ciee a radios 1 1 Chapters of this Publicati0N oooonooocccnnnnncnnoniococcccnnnccnnnnononcnnnnnnnnnnnnn nono nncnnnnnannnnnnos 1 1 MNS Chapter triciclo order wate tects al icon a aaa ta EASi 1 1 Importance of Audible and Intelligible Emergency Communications 0ee 1 2 Speech Intelligibility Importance 0 00 0 eee eect eter cette ee ee eee eeeeeeeeteeeeetneeeeetaa 1 2 Designing for Intelligibility cccecccceceeeceeeenee cece cece eeceaaeeeeeeeeesesenaeeeeeeeenseeennaeees 1 2 Chapter 2 Background Information 2 1 INTOQUCHION imita id drid aria oo 2 1 Inthis Chapter EE E EE E E E E E gaat vatotads rat 2 1 Basit A dio Mati enoni a na ea a 2 2 Ohm s Law and the Decibel niiin anana aera aaia aiian aaia 2 2 Adding Decibels nirna an a a a e ett aA 2 3 Sound and Hearing irer sei dieiieces enrik a di hot 2 4 The Relationship Between Sound and Hearing ccccceceeeeeeeeeeeeeeeeeeeeeeeeeeenatees 2 4 The Nature of Speech oooooococccccccccocococonccoccnnnnnononcnncnnnnnncnnnnnnnnnnn cnn nnnnnnn nn nnnnnnnnnnna
41. ements by adding the required signal to noise ratio usually 15dB to the background noise levels 3 From Step 1 select the wattage tap that satisfies the SPL requirements determined in Step 2 4 Multiply the wattage tap selection by the number of speakers in the room to determine the total audio power required This optional step is recommended for areas of high reverberation or of complex geometry Modern modeling tools such as EASE from Renkus Heinz and Modeler from Bose use sophisticated ray tracing algorithms to accurately predict intelligibility As part of system commissioning the audibility for every area must be verified This can be accomplished with a simple SPL meter set to read decibels with the A weighted filters applied The audibility of the primary evacuation signal is measured typically a temporal coded horn or slow whoop horn is used The audibility of emergency voice alarm communications messages is typically not recorded due to the varying nature of speech 6 2 Recommendations for Maximizing System Intelligibility Maximizing Intelligibility Use the following recommendations to maximize system 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 wit
42. ess Curves The equal loudness curves are used when sound levels are measured with a sound level meter If the meter has a flat response then the displayed result shows a larger than perceived level when sounds with significant low frequencies are measured For this reason sound level meters have a correction or weighting filter built in This filter can more closely match the displayed reading with the ear s response The most widely used weighting curve and the one required by NFPA 72 is the A weighted curve which is approximately the inverse of the 40 phon equal loudness curve Meters configured with the A weighted filter read out in units of dBA short for A weighted decibels Other common weighting curves are the B and C curves which approximate the ear s response at higher decibel levels From a practical standpoint these curves are useful for estimating the frequency content of the background noise during a room survey but cannot be used to validate the audibility of an emergency voice alarm communications signal Note The ear is capable of perceiving a difference in the sound level only when the sound level has roughly doubled or halved The dBA scale is a logarithmic scale so a doubling of sound power represents a 3 dBA increase in the SPL of the sound Therefore most listeners can not perceive changes in SPL of less than 3 dBA For a sound to be perceived as twice as loud the power must
43. ette neha Bee eis Vedia 6 6 Example 3 Gymnasii ornan n a A E A A 6 8 Example 4 LOND iia TO AR 6 10 CONCIUSION a o tilda 6 13 In GIOSING di ES antes ata Gade 6 13 Chapter 7 Glossary of Terms 7 1 Introduction 20 oe ee cece cece cece cece cece cece ecae cece eeeeececeaaaeeeeeeeeescsaaaeceeeeeeeseccaeaeeeeeeeeeessesnnieeeeess 7 1 lnsthis Chapter rocanrol sapetatscietinsessdedace te 7 1 GlossSaryisiectav acai A nan aii alin e 7 2 INdOX iia A een ee el eile IN 1 Related Publications Related Publications Refer to the publications and web sites listed below for more information regarding sound speech and audio intelligibility Acoustics The Construction and Calibration of Speech Intelligibility Tests ISO TR 4870 1991 E American National Standard Methods for Calculation of the Speech Intelligibility Index ANSI 3 5 1997 Handbook for Sound Engineers Third Edition Glen M Ballou Editor published by 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 Speech Intelligibility A JBL Professional Technical Note JBL Professional Northbridge CA Sound System Design
44. fire alarm applications Q is determined by Equation 2 10 Directivity Factor Q for a Conical Source For the speaker above the coverage angle 0 is 150 degrees at 2 kHz resulting in a Q of 2 7 Continued on next page 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 Polar Plot 2kHz 0 6dB division 10 high ceiling Critical Polar Angle A ay Fa oe Does PAR Ra CAE Listener level 93dB 99dB 5 1W 93dB Distance off axis Coverage Diameter 12 8 6dB variation Floor Figure 2 5 Speaker Coverage Coverage area is determined by a combination of speaker polar loss and the inverse square loss off axis To illustrate consider a speaker with no polar loss i e the speaker s SPL is the same over all angles As the listener moves away from the center of the speaker the distance to the speaker increases resulting in a lower SPL From the Inverse Square Law the off axis SPL is 6 dB lower than the on axis SPL when the distance from the speaker to the listener has doubled From simple geometry it can be determined that the maximum useable coverage
45. g mounted speaker Speaker Wattage Placement Edge to Edge Total Audio Power Calculate Listener Height Ambient Noise Required Signal to Noise Ratio Figure 6 1 iTool Office Space Example The following basic results are attained from the iTool e The iTool reverberation time calculator estimates a reasonable T60 time of 0 4 seconds Modest reverberation times are to be expected in a room with acoustic ceiling tile and carpeting e Using an Edge to Edge pattern the resulting total number of speakers is 135 tapped at 0 25 W for a total of 34 W of audio power required Continued on next page 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 i 2 C iTool 579 769 Examples iTool File Edit Options Help 0000600000 4 Project Room Data SPL Distribution Reverberation Time 8 corrivor Losey Room Width orice Room Length Unit Feet Room Height Speakers Required Speaker Tap Setting Total Power Required of Columns 0 of Rows Y First Speaker X Coord First Speaker Y Coord Room Length 340 Feet Column Spacing Row Spacing Figure 6 2 Office Space Speaker Location Guide
46. gns for many smaller occupancies can be accomplished satisfactorily if not optimally based upon experience with the performance of other systems in similar spaces For existing construction relatively simple acoustic measurements combined with knowledge of the chosen loudspeaker s performance characteristics can frequently result in satisfactory performance using mathematical formulas developed for the purpose For occupancies that do not yet exist the designer should have an understanding of the acoustic characteristics of the architectural design as well as the acoustic performance properties of available loudspeakers Architecturally this includes the physical size and shape of the space as well as the acoustic properties of the walls floors ceilings and interior furnishings A proper design analysis can sometimes reveal that an intelligible system is not achievable unless some features of the architectural design are changed The designer should be prepared to defend such conclusions and if necessary refuse to certify the installation of such a system While hand calculations and experience work well for simpler installations more complex designs are frequently better and more cost effectively analyzed using one of a number of readily available computer based design programs The designer and the authority having jurisdiction should both be aware that the acoustic performance parameters of the chosen loudspeakers as well as their
47. h respect to the speech signal Ensure adequate direct sound field coverage for the type of space Speaker layout pattern selection is critical in providing sufficient coverage at a reasonable cost In areas with high reverberation times it is possible to improve intelligibility by decreasing the separation between the loudspeakers and the listeners This increases the ratio of direct to reverberant sound and improves intelligibility but usually requires more loudspeakers to provide the same level of coverage Improve signal to noise ratio by putting speakers where people are located This assures good coverage and minimizes stray acoustical that adds to reverberation without contributing to intelligibility In rooms with high ceilings the areas near the edge of the room can be covered more effectively with wall mount speakers In areas with high ceilings directional speakers should be selected to avoid multiple speaker interactions Care must be taken to avoid signal distortion It is critical to ensure that signal levels are properly adjusted so that signal distortion does not occur Properly installed and maintained emergency voice alarm communications systems deliver low distortion by design Apply acoustic treatments to reduce reverberation 6 3 Applying the Methods Design Examples Example 1 Office Space The following examples illustrate the design methodology outlined earlier in this chapter For these examples computer
48. hard surface such as glass or marble has a low absorption coefficient This indicates that most of the energy is reflected back into the room Soft surfaces such as thick carpeting and acoustic ceiling tiles have high absorption coefficients Frequency content of reverberation depends on the surfaces as well Very hard surfaces such as tile reflect most of the frequencies while soft surfaces like drapes absorb most frequencies Most surfaces fall in between where higher frequencies are absorbed readily and lower frequencies are either passed through or reflected Reverberation is also affected by the room dimensions In general the larger the room the higher the reverberation times More precisely reverberation is dependent on the distance between opposing surfaces Two rooms with the same volume L x W x H and the same surface materials can have dramatically different reverberation times Continued on next page 2 6 Room Acoustics Continued Estimating Several equations are available for estimating the amount of reverberation that can be expected in Reverberation Times aroom 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 a lt 0 2 csi English Units ft Ts DAV a Sa T Metric Units m The Eyring Equati
49. he surfaces and furnishings These factors determine the reverberation time which influences intelligibility More sophisticated modeling tools provide accurate predictions of the reverberation time at any location within the modeled space Simple calculations however provide reasonably accurate assessments that are more than adequate for most installations Longer reverberation times require more care in the system design and even acoustical treatments to be applied to the room to achieve acceptable levels of speech intelligibility The lower the reverberation time the easier it is to provide a system with highly intelligible speech messaging Many spaces requiring emergency voice alarm communications systems inherently have low reverberation such as office buildings retail stores etc Acoustical treatments are rarely required and normal speaker layout rules apply Churches train stations airport etc on the other hand usually have high reverberation times and can require very special techniques to achieve acceptable intelligibility levels The sophisticated modeling tools may be required in these instances For most cases a simple calculation of reverberation time can be helpful Once the acoustical characteristics of the room are understood the speaker layout can be achieved Refer to the page number listed in this table for information on a specific topic Topic See Page Design Method 6 2 Recommendations for Maximizing Sys
50. ility 5 4 5 1 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 When performing a site investigation for speaker placement and power settings a survey of the area with a dBA reading sound level meter is used to determine the proper sound level required In sleeping areas the audibility requirements are the same except measurements are taken at the normal ear level for someone sleeping at pillow level From NFPA 72 2002 Edition 7 4 2 1 To ensure that audible public mode signals are clearly heard unless otherwise permitted by 7 4 2 2 through 7 4 2 5 they shall have a sound level 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 measured 1 5 m 3 ft above the floor in the occupiable area using the A weighted scale dBA When measuring tones the SPL must be maintained in all parts of the building however several cases recelve special consideration Elevators 7 4 2 2 and restrooms 7 4 2 5 are cited When determining the level of background noise it is not necessary to take into consideration sources such as construction equipme
51. ll 3 Gypsum over 2 x 4 16 o c Reverberation Time Wall 4 Gypsum over 2 x 4 16 oc Required Speakers Speaker Truedlert ceiling mounted speaker Speaker Wattage Placement Edge to Edge gt Total Audio Power Calculate Warning Additional modeling may be required Listener Height ix Reverberation time exceeds 2 seconds Ambient Noise Speaker to listener distance exceeds 12 3 66m Required Signal to Noise Ratio 15 Figure 6 9 iTool Gymnasium Example The following basic results are attained from the iTool e The iTool reverberation time calculator estimates a very high T60 time of 5 2 seconds Note Additional detailed modeling is most likely necessary due to the high T60 time e Using the Tool with an Edge to Edge pattern the resulting total number of speakers is 8 tapped at 0 25 W for a total of 2 W of audio power required Continued on next page 6 8 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 IC iTool 579 769 Examples iTool File Edit Options Help 2 eeeeeeeeee i 7 Calculation has finished You may click on the tabs below to review results 4 Project Room Data Speaker Location SPL Distribution Reverberation Time corrivor 5 Losey Room Width Feet O OFFICE Room Length Feet Unit
52. lls ceilings and other surfaces When a message is broadcast over a speaker system the listener hears a combination of the direct sound from the speakers plus the reflected or delayed sound from the reverberation Reverberation should not be confused with echoes An echo is a delayed but distinct reproduction of an original sound where reverberation contains the original sound jumbled into something not distinctly identifiable as part of the original signal 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 Reverberation Time also known as T60 times is the amount of time it takes for a sound to diminish to 60 dB below the original level For example to estimate a room s reverberation time pop a balloon in a room and time how long it takes for the sound to diminish The reverberation in a room is dependent on its dimension construction materials and objects within the room including the room s occupants People and furnishings are good sound absorbers Reverberation levels in occupied and or furnished rooms can be significantly lower than levels in unoccupied unfurnished rooms Each surface in a room absorbs or reflects a certain percentage of sound characterized by the Absorption Coefficient of the material The absorption coefficient is the ratio of absorbed to reflected sound and has a range of 0 to 1 A
53. milar 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 adequate intelligibility Care must be taken not to overextend the penetration into the room that can be expected from a wall mount speaker Rooms greater than 20 feet wide should not be treated with a single wall of speakers When designing a system where the opposite wall is greater than 15 feet away from the speaker minimum overlap or full overlap patterns should be selected See the figure below for typical wall mount speaker coverage pattern examples Edge edge Minimum Overlap Full Overlap Figure 2 9 Typical Wall Mount Speaker Coverage Layouts 2 18 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 While low frequencies vowels make up the largest power portion of the power of a speech signal it is the higher frequencies the consonants that contribute most to intelligibility
54. nnnnnnnn 2 5 INTOJUC t a DEEA E A EEE E de 2 5 Consonants and Vowels errire aen rea EERE AAE ERE E EAR EEEIEE 2 5 ROOM ACOUSUCS nenea E EAE AENEAS 2 6 aele LE laai o p PEET EEEE EE A E EA E EE E EE TEA 2 6 REVErberation mimica 2 6 Estimating Reverberation Times ooonnnncccnnnniccnnnoncccnnnoncnc nano ncn rc nano nc nr rana rar rnnn narra 2 7 Countering the Effects of Reverberation ooocoonnncccconocccccononcccnonannncnnnnnnnccnannnccnnnnnns 2 7 Speaker A AO 2 9 Inverse Square LW a ad idad si 2 9 S A A A a ea 2 10 Speaker Dispersion Angle and QU iooioccccccccccococonccnnnconnnnnnnnnnncnnnnnnnnnnnnnnnnnnnnnnnnnns 2 10 Speaker COVERAGE iia rl bodas 2 12 Determining Critical Polar ANgl8 ooonnocccnnnnnicinnnniccnnnnonccnnnannnncnnonnnr nano nn rra rca 2 13 Determining Critical Polar ANg Esera ritrinita rere nc nr nana nn rro rca 2 14 Power Rad acidos ian ates dy Heat nueeenete needeed diated 2 15 Speaker Layou enire E a A beeetiantoheeeeted leeks lata tecte lanier 2 15 Distributed Wall Mounted SysteMS oooooonnccccnnnnoccccnnnoncccnnnoncccnn cnn cnn nan nn rc rn anar rc 2 16 INTFOQUCHION aea iio dilcrd 2 16 AUNADO cti ad 2 16 Disadvantages di 2 16 Design of a Distributed Wall Mount SysteM ooooonccccnnnccccnnnocccccononcncnnnnoncccnanancnnnnnna 2 17 Chapter 3 Speech Intelligibility 3 1 Intro dUCI ON scarico nach iabdiiee eased 3 1 INthis Chapter icon lada 3 1 Influences on Intelligibilitty icccu i dee ste tocara ds 3 2
55. ns systems and describes the advantages of an emergency system compared to a typical non emergency paging system e Chapter 5 Regulatory Issues Discusses National Fire Protection Agency NFPA Codes Several excerpts of the 2002 Code are included e Chapter 6 Fire Alarm Audio Speaker System Design Method Provides examples of speaker designs created by using the Tyco Safety Products iTool e Chapter 7 Glossary of Terms This chapter includes definitions of the important terms used in this publication Refer to the page number listed in this table for information on a specific topic Topic See Page Importance of Audible and Intelligible Emergency Communications 1 2 1 1 Importance of Audible and Intelligible Emergency Communications Speech Intelligibility Importance Designing for Intelligibility Emergency voice alarm communications systems are used in applications where it is necessary to communicate more detailed 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 people trying to exit at once 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 a
56. nt or other sources that would not normally be present It is however required to take into consideration normal noise sources that last longer than 60 seconds vacuum cleaners are cited as an example in Annex A 7 4 1 3 When designing for new construction where a survey is not possible Annex A of NFPA 72 provides guidance of the anticipated ambient sound level From NFPA 72 2002 Edition A 7 4 2 The typical average ambient sound level for the occupancies specified in Table A 7 4 2 are intended only for design guidance purposes The typical average ambient sound levels specified should not be used in lieu of actual sound level measurements Table A 7 4 2 Average Ambient Sound Level According to Location Location Average Ambient Sound Level dBA Business occupancies 55 Educational occupancies 45 Industrial occupancies 80 Institutional occupancies 50 Mercantile occupancies 40 Mechanical rooms 85 Piers and water surrounded structures 40 Places of assembly 55 Residential occupancies 35 Storage occupancies 30 Thoroughfares high density urban 70 Thoroughfares medium density urban 55 Thoroughfares rural and suburban 40 Tower occupancies 35 Underground structures and windowless buildings 40 Vehicles and vessels 50 Note Audibility must be verified at the time of system commissioning and periodically verified in accordance with the requirements stated in the Inspection Testing and Maintenance chapter of NFPA 72 Co
57. ntinued on next page 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 5 3 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 measu
58. ome of these factors are under the control of the system designer however many are not The challenge of good audio system design is to compensate for the factors which cannot be controlled This ensures that the system installed can provide intelligible messages in emergency situations Continued on next page 3 2 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 In general if the speech signal is 10 dB higher than the noise the intelligibility loss due to background noise is minimal The figure below shows degradation as a function of signal to noise ratio CIS Degradation from Background Noise Broad Spectrum 0 95 o Ko 0 85 0 8 0 75 o y 0 65 Intelligibility CIS Scale o ao ao 4 3 2 1 O0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Signal to Noise Ratio dBA e a Figure 3 3 Degradation of CIS vs Signal to Noise Ratio Note There are limits to increasing the speech signal to noise ratio Above approximately 90
59. on used when a gt 0 2 l 0 049 V 0 16 V T English Units ft T Metric Units m S In 1 a S In 1 a Where V Room Volume L x W X H S Total Surface Area 2LH 2LW 2WH a Average absorption coefficient equal to the area of each surface multiplied by the absorption coefficient for that surface divided by the total surface area of the room Equation 2 7 Sabine and Eyring Formulas for Calculating Reverberation Times Countering the Effects of Reverberation Adding drapes wall hangings carpeting or specially designed diffusers can absorb sound and reduce reverberation If possible this is perhaps the best method in combating reverberation e Acoustical treatment Note Final room acoustics are often unknown at the time of the system design e Speaker Placement Because reverberation is caused by reflections it is important to select speaker locations that minimize stray energy Sound system designers are often heard saying put the sound where people are and do not put sound where people are not This usually implies locating speakers toward the center of the room away from walls and other hard surfaces When possible aim speakers towards soft surfaces such as rugs or upholstered furnishings These soft surfaces absorb direct sound coming from the speaker preventing the sound from scattering throughout the room Continued on next page 2 7 Room Acoustics Continued Co
60. ons related v R RASTI 3 7 regulatory issues 5 1 related publications v reverberation 2 6 3 4 7 3 Reverberation estimating times 2 7 riser 4 3 7 3 riser analog 4 3 riser digital 4 3 riser fiber optic 4 3 Robinson and Dadson equal loudness curves 2 4 room design calculator 6 4 S Sabine and Eyring equations 2 7 sensitivity 7 3 signal to noise ratio increasing 2 8 sound pressure levels SPL 7 3 Sound Pressure Levels SPL 2 2 speaker circuits 4 4 speaker coverage 2 12 speaker dispersion angle 2 10 Speaker layout patterns 2 15 speaker placement 2 7 speaker sensitivity 2 10 speech pattern 3 4 speech pattern modulations 2 5 STI method 3 7 7 3 STI CIS Intelligibility Measurement System 3 8 STIpa 3 7 STITEL 3 7 system design tools 3 9 IN 2 T transponder 4 3 7 3 Vv voice alarm systems 4 2 W wall mounted speakers 2 16 wall mounted speakers advantages 2 16 wall mounted speakers design 2 17 wall mounted speakers disadvantages 2 16 word scores 3 7 579 769 Rev C FIRE SECURITY COMMUNICATIONS WORKFORCE SOLUTIONS WORLDWIDE SALES amp SERVICE 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
61. overage Information Continued on next page 6 9 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 Figure 6 13 Lobby Example Lobby Example e Dimensions 24 Lx 16 Wx 10 H e Flooring Tile e Ceiling Acoustic Tile e Walls Three Walls of Finished Wood One Glass e Ambient Noise 50 dB AC iTool 579 769 Examples Too DER File Edit Options Help 0000060000 F Iculat a Ye the t e Q Proiect Room Data Speaker Location SPL Distribution Reverberation Time CORRIDOR Room Length wih Heit gm Dimension 24 16 10 Feet OFFICE Floor GYM Marble or Glazed Tile Ceiling Tectum 1 Acoustic Ceiling Tile wali Glass Wall2 PlywoodPaneling 0 75 Well3 Plywood Paneling 0 75 Reverberation Time Wall 4 Plywood Paneling 0 75 Required Speakers Speaker Trmue lert ceiling mounted speaker gt Speaker Wattage Placement Edge to Edge TotalAudio Power Calculate A Spacing Listener Height 5 Feet Ambient Noise Required Signal to Noise Ratio 15 dB Figure 6 14 Lobby Example The following basic results are
62. quation covered in Chapter 2 of this manual Continued on next page 7 2 Glossary Continued Glossary or Terms continued DISTORTION The undesired change in the waveform of a signal that can lead to diminished clarity in reception or reproduction ECHO The repetition of sound by reflection of sound waves from a surface FIBER OPTIC RISER An analog or digital risers that uses fiber optic distribution media Fiber optic systems have the advantage of immunity to electrical noise and Earth faults FREQUENCY The number of repetitions per unit time of a complete waveform as of an electric current INTELLIGIBILITY The capability of being understood or comprehended INVERSE SQUARE LAW A drop in Sound Pressure Levels SPLs is referred to as the Inverse Square Law The law originates from the fact that as the diameter of the sound sphere doubles the surface area increases by a factor of four This behavior of outwardly radiating sound causes a drop in SPL of 6dB per doubling of distance See Chapter 2 of this manual to see this law applied 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 One tone has twice as many vibrations pe
63. r second as the other OHM s LAW Electrical current is directly proportional to voltage and inversely proportional to resistance I F R PHON A unit of subjective loudness PHONEMES The sounds that make up spoken words POLAR PLOTS The correlation between speaker SPL and off axis angle that is occasionally provided by manufacturers REVERBERATION Also known as T60 times is the amount of time it takes for a sound to diminish to 60 dB below the original level Reverberation is produced when sound reflects off walls and other surfaces What the listener hears is the direct sound from the speaker plus the reflected sound from the reverberation RISER The riser is the wiring that connects the command center with the amplification equipment There are several types of risers depending on the application Analog Digital and Fiber Optic SENSITIVITY The sensitivity is the amount of sound Sound Pressure Level produced by the speaker with a known signal frequency power level and distance from the speaker SOUND PRESSURE LEVELS SPL s The level of sound pressure that is typically expressed in decibels STI METHOD An intelligibility measurement method that 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 TRANSPONDER Receives the riser from the command center amplifies and distribute
64. rements 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 From NFPA 72 2002 Edition 7 4 1 4 Where required emergency voice alarm communications systems shall be capable of the reproduction of prerecorded synthesized or live e g microphone telephone handset and radio messages with voice intelligibility Working without a preset limit gives the AHJ latitude to determine adequate intelligibility NFPA 72 provides guidance for determining adequate intelligibility with the explanatory information in the Annex From NFPA 72 2002 Edition A 7 4 1 4 Voice intelligibility should be measured in accordance with the guidelines in Annex A of IEC 60849 Second Edition 1998 Sound systems for emergency purposes When tested in accordance with Annex B Clause B1 of IEC 60849 the system should exceed the equivalent of a common intelligibility scale CIS score of 0 70 Intelligibility is achieved when the quantity lav as specified in B3 of IEC 60849 exceeds this value lav is the arithmetical average of the measured intelligibility values on the CIS and sigma is the standard deviation of the results Objective means of determining intelligibility are found in Part 16 of IEC 60268 The objective rating of speech intelligibility by
65. rrive at the scene and alarm paging systems can also be used to deliver live spoken messages from the emergency personnel to the occupants In this Chapter Refer to the page number listed in this table for information on a specific topic Topic See Page A Typical Emergency Voice Alarm Communications System 4 2 Parts of an Emergency Voice Alarm Communications System 4 3 4 1 A Typical Emergency Voice Alarm Communications System Typical Emergency The figure below illustrates a typical emergency voice alarm communications system Voice Alarm Communications System Command Center Transponder Microphone Audio Controller Amplifie ler with backup battery Supervised Speaker 7 H z o Routing Remote O Switches Microphones 0000 Multi Story Building Figure 4 1 Typical Emergency Voice Alarm Communications System While an emergency voice alarm communications system is similar to a non emergency paging system there are certain features that make emergency systems much more reliable than standard paging systems Advantages e Backup Power Source Batteries or Generator Allows the system to operate for as long as several days during a power failure e 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 e Supervision of All Critical Signal Paths From the microphone through the las
66. s PES AE E ae AEN 6dB_ ls 3 off wall e omen Width nal CLX NXXX XIX SOONER SE SONOS X XxX Figure 2 8 Wall Mount Speaker Coverage Pattern The coverage patterns for wall mount speakers are the same for distributed overhead systems with the goal of minimizing SPL variations in the protected area Equation 2 11 can be applied to wall mounted systems by replacing the speaker to listener distance D2 with the room width minus 3 feet In a wall mounted system it is generally more appropriate to consider the diameter of coverage rather than the coverage area The coverage diameter defines the width of wall coverage and ultimately the speaker spacing depending on the coverage overlap pattern Table 2 4 Wall Mounted Speaker Coverage Width Vs Room Depth Wall Mounted Speakers In Feet Wall Mounted Speakers In Meters Coverage Width Room Coverage Width 3 Feet from Wall Width 1 Meter from Wall Opposite Speaker Opposite Speaker 10 Feet 18 Feet 2 5 Meters 3 8 Meters 12 Feet 23 Feet 3 0 Meters 5 1 Meters Room Width 14 Feet 28 Feet 3 5 Meters 6 4 Meters 16 Feet 33 Feet 4 0 Meters 7 7 Meters 18 Feet 38 Feet 4 5 Meters 9 0 Meters 20 Feet 44 Feet 5 0 Meters 10 2 Meters 5 5 Meters 11 5 Meters 6 0 Meters 12 8 Meters Continued on next page 2 17 Distributed Wall Mounted Systems Continued Design of a The coverage patterns for a distributed wall mount system are si
67. s signals to the speaker circuits The transponder also interfaces to detection equipment and other signaling circuits strobes deluge valves etc and communicates status back to the command center 7 3 Index ALcons 3 7 A acoustical treatment 2 7 acoustics 2 6 AHJ 7 2 Amplifiers 4 3 audibility 5 2 7 2 audio riser interface modules 4 3 B background noise 3 3 5 3 C Ceiling height 2 14 CIS 3 6 7 2 clipping 7 2 combination system 7 2 command center 4 3 7 2 Common Intelligibility Scale CIS 3 6 constant voltage 7 2 coverage angle 7 2 critical polar angle 2 13 2 14 7 2 D dB and distance chart 2 9 decibel 7 2 Decibel 2 2 decibels adding 2 3 design method 6 2 digital riser 7 2 directivity factor 2 11 directivity factor 7 2 distortion 3 5 7 3 distributed speaker 3 9 E echo 7 3 emergency voice evacuation systems 1 1 emergency voice alarm communications system 4 2 equal loudness curves 2 4 F fiber optic riser 7 3 fire alarm audio systems 4 3 frequency 7 3 IN 1 G Glossary of Terms 7 1 I intelligibility 3 2 5 4 7 3 Intelligibility 1 1 intelligibility certification 5 5 inverse square law 2 9 7 3 M Microphone technique 3 5 N NACs 4 3 NFPA 7 3 O Ohm s Law 2 2 7 3 Overview 1 1 P percent ALcons 3 7 phon 7 3 phonetically balanced word scores 3 7 polar plots 2 10 7 3 power ratings 2 15 publicati
68. speech transmission index Subject based techniques for measuring intelligibility are defined by ANSI S3 2 Method for Measuring the Intelligibility of Speech Over Communications Systems ANSI S3 2 should be considered an acceptable alternative to ISO TR 4870 where referenced in IEC 60268 Part 16 Second Edition 1998 The objective rating of speech intelligibility by speech transmission index As technology for intelligibility analysis equipment advances many expect the main body of NFPA 72 will be changed to require a minimum fixed intelligibility score that is verifiable with the equipment designed for this purpose The SimplexGrinnell STICIS meter and TALKBOX signal generator is the first such system developed to provide a measurement system that is nearly as easy to use as a dBA meter provides readout in CIS units and is portable Note See the Measures of Intelligibility section in Chapter 3 of this guide for more information The system uses a subset of the STI method outlined in IEC60628 Continued on next page Intelligibility Continued Intelligibility continued Intelligibility Certification There is significant explanatory information in Annex A recently revised for the 2002 edition 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 desi
69. stical factors that influence intelligibility awareness of the tools available 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 This 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 1 2 Introduction In this Chapter Chapter 2 Background Information 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 section at the beginning of this manual for publications containing in depth discussions of sound and speech Refer to the page number listed in this table for information on a specific topic See Page Basic Audio Math 2 2 Sound and Hearing 2 4 The Nature of Speech 2 5 Room Acoustics 2 6 Speaker Basics 2 9 Distributed Wall Mounted Systems 2 15 2 1 Basic Audio Math Ohm s Law and the Decibel
70. t speaker in the system all wiring is supervised for shorts opens and Earth faults e Access Control Locked cabinet permits only authorized personnel to access to the system e 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 e Local Mode Operation Alarm signals are available even if amplifiers lose communications with the command center 4 2 Parts of an Emergency Voice Alarm Communications System Command Center Audio Riser Transponder 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 This area typically includes the equipment required to generate and distribute messages throughout the building s emergency network Voice paging equipment in the command center typically includes e A dedicated master microphone e Speaker selection switches routing switches used to select paging zones that cover the entire building or specific areas e System auxiliary audio inputs including remote microphones and connections to other emergency systems e Recorded messages for automatic voice announcements e Signal processing electronics e Emergency personnel phone equipment e Audio riser distribution amplifiers Note Itis possible to have m
71. tem Intelligibility 6 3 Applying the Methods 6 4 Conclusion 6 13 6 1 Speaker Design Method Introduction Step 1 Room Characteristics Step 2 Calculate the Number of Speakers Step 3 Audio Power and Individual Speaker Wattage Tap Step 4 Model Design to Predict Intelligibility Step 5 Verify Final Installation 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 Determine if the room requires advanced design methods Some characteristics of a difficult location space include e High Background Noise Levels Greater than 80 dB e Large Spaces with High Ceilings Greater than 15 foot high ceilings e Unique Room Shapes Rooms with many different angles spherical shapes etc e High Reverberation Times T60 gt 1 5 Use the steps below to calculate the number of speakers 1 Determine the speaker to listener distance D2 2 Using D2 and the speaker s polar response calculate the speaker s coverage area 3 Select a layout pattern and calculate the number of speakers required for the area Use these steps below to determine the required audio power 1 Using the speaker s sensitivity and speaker to listener distance calculate the listener SPL for each of the wattage taps Subtract the SPL variation based on the coverage pattern from Table 2 3 2 Determine the SPL requir
72. tribute messages throughout the building s fire alarm audio network CONSTANT VOLTAGE Speakers used for a distributed emergency evacuation system are wired as a Constant Voltage system where the voltage at each speaker is the same typically 25V or 70 7V at the maximum power output of the amplifier COVERAGE ANGLE The angle where the speaker Sound Pressure Level SPL drops 6 dB from the on axis SPL COVERAGE AREA The plane where the Sound Pressure Level SPL at the edge of the plane drops 6 dB below the on axis SPL CRITICAL POLAR ANGLE The angle where the sum of the distance loss and the polar loss is 6 dB less than the on axis Sound Pressure Level SPL DECIBEL A unit used to express relative difference in power usually between acoustic or electric signals equal to ten times the common logarithm of the ratio of two power levels or 20 times the common logarithm of the ratio of two voltage levels DIGITAL RISER A digital system that transmits multiple channels of digital audio throughout a facility A single pair of wire is used to transmit up to eight channels of digitally encoded audio signals The digital riser is considered a signaling line circuit and is wired in a Style 4 or Style 7 configuration DIRECTIVITY FACTOR Q A common representation of speaker directivity for speakers having a conical coverage pattern typical of single driver speakers used in fire alarm applications Q is determined by an e
73. ty levels The two listed programs require significant training and expertise to use as well as a fair amount of time to build models that are complete enough to provide accurate results For small to medium sized projects it usually is not cost effective to use these modeling tools However for larger or more complex projects the costs of modeling tools are easily justified It is much less expensive to use the modeling tools to design the system properly the first time than to have to troubleshoot problems after installation For the smaller projects typical in a fire alarm layout Tyco Safety Products has developed software called Tool that can be used to design a speaker system that meet requirements for most areas This tool is not an acoustical modeling package It is designed to assist the Speaker System Designer with calculations of reverberation and assist with speaker placement Note See Chapter 6 of this manual for design examples that use the iTool Refer to the Tool Installation and User s Guide 579 772 for more information 3 9 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 a
74. udible loud enough or if it is not intelligible understandable then emergency information is not properly communicated Therefore a safe response to a fire 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 sense 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 been 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 recognized the importance of requiring both audibility and intelligibility Although a specific measure of intelligibility is not currently required by NFPA 72 the Code s Annex recommends the use of International Electrotechnical Commission IEC 60849 and a Common Intelligibility Scale CIS measurement of 0 70 as a guideline It is expected that future versions of NFPA 72 will quantify the measurements required to demonstrate intelligibility Properly designing emergency voice alarm communications systems for intelligibility requires knowledge of the acou
75. ultiple command centers within a emergency network each with a microphone and speaker select switches However only one command center may be in control at a time with a clear indication of who is in control The audio riser is the wiring that connects the command center with the amplification equipment There are several types of risers depending on the application e Analog Riser A system with only one or two channels uses analog risers where only one channel is transmitted on a pair of wires The analog riser uses shielded wire to prevent noise pickup as it travels throughout the building It can be configured for Class A or Class B operation e Digital Riser Applications needing more than two channels use a digital system that transmits multiple channels of digital audio throughout the building A single pair of wires is used to transmit up to eight channels of digitally encoded audio signals The digital riser is considered a Signaling Line Circuit SLC and is wired in a Style 4 or Style 7 configuration e Fiber Optic Riser The analog riser and digital risers are available with a fiber optic distribution media Fiber optic systems have the advantage of immunity to electrical noise and Earth faults A transponder receives the riser from the command center amplifies and distributes signals to the speaker circuits The transponder also interfaces to detection equipment and other signaling circuits strobes deluge valves etc
76. ume levels the A weighted correction curve is applied to SPL measurements to equalize the loudness of sounds over the hearing range Meters configured with the A weighted filter read out in units of dBA short for A Weighted Decibel 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 CIS The Common Intelligibility Scale is a standardized scale that correlates a variety of intelligibility measurement methods CLIPPING When part of the electrical signal path exceeds the capacity of the component audio Clipping can occur causing a reduction in intelligibility COMBINATION SYSTEM A fire alarm system that is also used for non fire alarm functions Combination Systems contain not only typical configurations of fire alarm and emergency voice alarm communications systems but also sound systems for background music and paging for non emergency messaging COMMAND CENTER The area of a building usually near the entrance that acts as the communications center for emergency personnel The command center is used to display the fire alarm system status and control the annunciation system This area typically includes the equipment required to generate and dis
77. untering the Effects of Reverberation continued Increasing the Signal to Noise Ratio Intelligibility degradation from reverberation is essentially a signal to noise issue however when the noise is specifically caused by reverberation it is referred to as the Direct to 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 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 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 999 Note See the section later in this chapter entitled Speaker Dispersion Angle and Q for more information Speaker Basics Inverse Square Law Speakers are essentially point sources of sound Sound radiates outward in all directions creating a spherical sound
78. ure carpeting etc If the Certificate of Occupancy CO requires intelligibility testing before signing off on the installation certain factors should be considered e Consider designing to the worst case conditions This is usually an unfurnished room the addition of absorbing materials enhance intelligibility e Audibility measurements taken in an unfurnished area can drop by as much as 3 dB with the addition of absorptive materials e For large areas where the reverberation times are expected to drop dramatically request a delay in intelligibility testing until furnishings are added 5 5 Introduction In this Chapter Chapter 6 Speaker System Design Method 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 Achieving an acceptable level of intelligibility by trial and error can be extremely costly A systematic approach to the design using basic guidelines and simple models can yield excellent results with a minimum investment of time It is important to understand the physical and acoustical characteristics of the space in which the system is installed This requires rough measurements or estimates of the dimensions of the space and basic acoustical characteristics of t
79. xamples of different settings such as office spaces gymnasiums and corridors to demonstrate the differences in reverberation time Continued on next page Influences on Intelligibility Continued Distortion Microphone Technique Distortion of the speech waveform can come from many sources however it is usually exhibited by an overdriven signal causing the peaks of the waveform to be clipped 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 Because clipping itself does not reduce modulations the intelligibility effects of clipping are generally not as severe as noise and reverberation effects A properly installed operated and maintained Simplex Fire Alarm Audio System has minimal distortion and reproduces speech with excellent clarity Proper microphone technique can be a major speech intelligibility factor in emergency voice alarm communications systems Unfortunately this is one area over which the system designer has no control Although this is not normally considered during the measurement of speech intelligibility or during system acceptance testing it should be considered in the training and use of the system For this reason when possible use of pre recorded messages or digitally compile

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