Tyco 579-769 User Manual

Fire Alarm Audio Applications Guide Guideline for Designing Emergency Voice/Alarm Communications Systems for Speech Intelligibility 579-769 Rev

1-2 Emergency voice/alarm communications systems are used in applications where it is necessary to communicate more detailed information to occupan

2-1 There are a few fundamental concepts that are necessary to understand when working with emergency voice/alarm communications systems. This cha

2-2 Audio engineers use “Decibels” (dB) to express ratios between levels, such as power, Volts, Amps, and Sound Pressure Levels (SPL). The decibel

2-3 When the decibel is used to express SPL, the reference sound pressure is 20 x 10-6 Newtons/m² which is approximately the threshold for hearing

2-4 Sound is created by mechanical vibrations that displace air molecules to create repetitive changes in air pressure. The ear detects these chang

2-5 The frequency of speech ranges over seven octaves from 125 Hz to 8,000 Hz, with the majority of frequencies contributing to intelligibility fal

2-6 This section is provided as a summary of room acoustics. See the references in the “Related Documentation” section earlier in this manual for

2-7 Several equations are available for estimating the amount of reverberation that can be expected in a room. The equations take into account the

2-8 • Increasing the Signal-to-Noise Ratio: Intelligibility degradation from reverberation is essentially a signal-to-noise issue, however when th

2-9 Speakers are essentially “point sources” of sound. Sound radiates outward in all directions, creating a spherical sound pattern. The sound pre

2-10 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 liter

2-11 The figure below includes a typical polar plot graph and the interpretation of the dispersion angle. 87dB87dBSensitivity = 93dB @10 Feet, 1 W

2-12 Using the polar information of the speaker, in combination with the distance between the speaker and the listener, you can determine the area t

2-13 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

2-14 Once the critical polar angle has been determined, calculate the coverage area for a given speaker-to-listener distance: Coverage Circle Diame

2-15 Speakers used for emergency voice/alarm communication system are wired as “Constant Voltage” systems, where the maximum power output of the amp

2-16 The preceding sections apply primarily to ceiling mounted speakers, generally referred to as “Distributed Overhead Systems.” Another useful m

2-17 The design of a distributed wall mount system is similar to an overhead system, with some important differences. In a wall mount system the s

2-18 The coverage patterns for a distributed wall mount system are similar to ceiling mount designs, except only a single row is used in the patter

3-1 Intelligibility is a measure of the capability of a message to be comprehended. In simplest terms, it is the reduction of the modulations of sp

Copyright © 2005 Tyco Safety Products – Westminster. All rights reserved. All specifications and other information shown were current as of docu

3-2 The figure below lists the relative contributions of each frequency band: Octave Band Contribution to Intelligibility0%5%10%15%20%25%30%35%125

3-3 Background noise causes a reduction in signal-to-noise ratio over all frequencies and modulations. Consider the comparison of the speech signal

3-4 Some types of background noise have a greater impact on intelligibility than others depending on the frequency content of the noise. Noise gene

3-5 Distortion of the speech waveform can come from many sources, however it is usually exhibited by an overdriven signal, causing the peaks of the

3-6 International Electrotechnical Commission (IEC) 60849 defines intelligibility as: “a measure of the proportion of the content of a speech messa

3-7 As described in Chapter 2, speech consists of the frequency of the sound being uttered and the amplitude modulation of that sound into the phon

3-8 Measurement of intelligibility can be complicated, and it sometimes includes subjective analysis. To effectively implement intelligible system

3-9 Several tools varying in levels of complexity can assist the sound system designer in producing a system of acceptable intelligibility. These r

3-10

4-1 An emergency voice/alarm communications system is designed to provide a highly reliable voice reinforcement and distribution network. These sy

4-2 The figure below illustrates a typical emergency voice/alarm communications system: Figure 4-1. Typical Emergency Voice/Alarm Communication

4-3 A command center should be located at the building entrance and act as a communications center for emergency personnel. The command center is u

4-4 Speaker circuits convert electrical power from amplifiers into sound. These circuits are wired in a daisy-chain fashion, with a single path of

5-1 The governing specifications for the US Fire Alarm Market are found in the installation standard, NFPA 72® “National Fire Alarm Code.” The fir

5-2 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 th

5-3 To meet the 15 dBA requirement, there are cases where high levels of background noise require extremely high levels of emergency annunciation t

5-4 Intelligibility has historically been a difficult parameter to measure. Unlike SPL that can easily be measured with a relatively common dBA met

5-5 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 desi

5-6

6-1 This chapter covers a design methodology that can be used to design a speaker system for an emergency voice/alarm communications system. The a

iii Chapter 1 Speech Intelligibility Overview 1-1 Introduction ...

6-2 The steps below summarize the speaker system design method. Use these steps in conjunction with the Tyco Safety Products iTool (described late

6-3 Use the following recommendations to maximize system intelligibility: • Ensure at least an 8 dBA signal-to-noise ratio with regard to the spee

6-4 The following examples illustrate the design methodology outlined earlier in this chapter. For these examples, computer based modeling was emp

6-5 Click the “Speaker Location” tab on the iTool for more detailed information. The following screen shows a speaker location guide for the offic

6-6 In this example, consider a standard office corridor with the following specifications: • Dimensions = 100’ L x 12’ W x10’ H • Flooring

6-7 Click the “Speaker Location” button on the iTool for more detailed information. The following screen shows a speaker location guide for the cor

6-8 Gymnasiums are notoriously bad acoustic environments. Extremely high reverberation times can be expected because of the large room volume plus

6-9 Click the “Speaker Location” button on the iTool for more detailed information. The following screen shows a speaker location guide for the gy

6-10 During an intelligibility survey in an office building, an employee lobby area measured 0.60 CIS intelligibility, failing the NFPA suggested 0.

6-11 The existing design had two wall mounted speakers, to the left and right of the entrance doors. Figure 6-15. Lobby Layout The following scr

ivInfluences on Intelligibility... 3-2 Introduction ...

6-12 The following screen shows the reverberation time and speaker coverage information: Figure 6-18. Lobby Reverberation Time and Speaker Cove

6-13 Designing Emergency Voice/Alarm Communications Systems for Speech Intelligibility requires awareness of the area dimensions, anticipated backg

6-14

7-1 This chapter contains a glossary of technical terms that are used throughout this manual. Refer to the page number listed in this table for in

7-2 This list provides brief descriptions of various terms relating to this publication: ABSORPTION COEFFICIENT – The ratio of absorbed-to-reflected

7-3 DISTORTION – The undesired change in the waveform of a signal that can lead to diminished clarity in reception or reproduction. ECHO – The repe

7-4

IN-1 % %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 ba

IN-2speaker dispersion angle, 2-10 Speaker layout patterns, 2-15 speaker placement, 2-7 speaker, sensitivity, 2-10 speech pattern, 3-4 speech patter

vStep 1: Room Characteristics... 6-2 Step 2: Calculate the Number o

7-1 579-769 Rev. C Printed in the U.S.A. Specifications and other information shown were curre

vi Refer to the publications and web sites listed below for more information regarding sound, speech, and audio intelligibility: • Acoustics – Th

1-1 INTELLIGIBILITY – The capability of being understood or comprehended. In simple terms, intelligibility is an evaluation of changes that occur t