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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.
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Copyrights and Trademarks Copyrights 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. Trademarks 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 th
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Table of Contents Chapter 1 Speech Intelligibility Overview 1-1 Introduction .............................................................................................................. 1-1 Chapters of this Publication..................................................................................... 1-1 In this Chapter ......................................................................................................... 1-1 Importance of Audible and Intelligible Emergency Commun
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Influences on Intelligibility............................................................................................ 3-2 Introduction .............................................................................................................. 3-2 Background Noise ................................................................................................... 3-3 Reverberation ..........................................................................................................
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Step 1: Room Characteristics................................................................................ 6-2 Step 2: Calculate the Number of Speakers ........................................................... 6-2 Step 3: Audio Power and Individual Speaker Wattage Tap .................................. 6-2 Step 4: Model Design to Predict Intelligibility......................................................... 6-2 Step 5: Verify Final Installation .............................
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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 S3.5-1997). • Handbook for Sound Engineers, Third Edition, Glen M. Ballou, Editor, published by Butterworth-Heinemann, W
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Chapter 1 Speech Intelligibility Overview Introduction INTELLIGIBILITY – The capability of being understood or comprehended. In simple terms, intelligibility is an evaluation of changes that occur to speech that impact comprehension. More specifically, intelligibility is concerned with evaluating 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 n
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Importance of Audible and Intelligible Emergency Communications Speech Intelligibility Emergency voice/alarm communications systems are used in applications where it is necessary to Importance 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 block
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Chapter 2 Background Information Introduction There are a few fundamental concepts that are necessary to understand when working with emergency voice/alarm communications systems. This chapter introduces basic concepts of sound, but is not intended to be an exhaustive treatment of the subject. Note: Refer to the “Related Documentation” section at the beginning of this manual for publications containing in-depth discussions of sound and speech. In this Chapter Refer to the pag
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Basic Audio Math Ohm’s Law Audio engineers use “Decibels” (dB) to express ratios between levels, such as power, Volts, and the Decibel Amps, and Sound Pressure Levels (SPL). The decibel is not an absolute measure like Volts and Amps, rather it is used to make comparisons between two numbers. The decibel is defined as the logarithm of two power levels, shown below in the equation as P and P : 1 0 P1 ⎛ ⎞ Decibel =10log ⎜ ⎟ P0 ⎝ ⎠ Equation 2-1. The Decibel P is the referenc
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Basic Audio Math, Continued -6 Ohm’s Law When the decibel is used to express SPL, the reference sound pressure is 20 x 10 Newtons/m² and the Decibel, which is approximately the threshold for hearing for a normal listener. When using a dB meter to (continued) measure sound, the meter is performing the calculation between the received SPL and the reference SPL: SPL ⎛ ⎞ dB = 20log ⎜ ⎟ spl −6 20 ×10 ⎝ ⎠ Equation 2-5. dB and Sound Pressure Levels Adding Decibels When multipl
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Sound and Hearing The Relationship Sound is created by mechanical vibrations that displace air molecules to create repetitive changes Between Sound in air pressure. The ear detects these changes in air pressure, with the magnitude of the pressure and Hearing perceived as loudness and the frequency of the changes perceived as pitch. 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 sen
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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 frag
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Room Acoustics Introduction 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 Reverberation is one of the most important contributors to reduced intelligibility, and is the result of sound being reflected off floors, walls, ceilings and other surfaces. When a message is broadcast over a speaker sys
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Room Acoustics, Continued Estimating Several equations are available for estimating the amount of reverberation that can be expected in Reverberation Times a room. The equations take into account the room dimensions and surface materials to provide a reasonably accurate estimation of a rectangular room’s reverberation time. The formulas below are commonly used Sabine and Eyring equations: The Sabine Equation, used when α < 0.2: 0.049 V 0.16 V T = English Units (ft) T = Metr
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Room Acoustics, Continued Countering the • Increasing the Signal-to-Noise Ratio: Effects of Intelligibility degradation from reverberation is essentially a signal-to-noise issue, however Reverberation, when the noise is specifically caused by reverberation it is referred to as the “Direct-to- (continued) Reverberant” ratio. Increasing the direct sound field at the listener improves the direct to reverberant ratio and therefore the signal-to-noise ratio. You can increase the direc
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Speaker Basics Inverse Square Law Speakers are essentially “point sources” of sound. Sound radiates outward in all directions, creating a spherical sound pattern. The sound pressure is spread over an increasingly larger surface area as the sound moves away from the source. This causes a drop in loudness per unit area. 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
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Speaker Basics, Continued Sensitivity 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, the sensitivity is rated at 1 W of power and 10 feet (3 meters) from the speaker. By knowing t
