Improving Intelligibility of Airport Terminal Public Address Systems (2017) / Chapter Skim
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Pages 28-39
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From page 28... ...
28 4.1 General Acoustical Principles This chapter presents and discusses the acoustical principles that affect the speech intelligibility of PA systems in enclosed spaces such as airport terminals. To present background information to understand these principles, this section introduces the basic concepts of acoustics, including how sound is measured.
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physical Factors affecting pa Intelligibility 29 Figure 4-1. The six physical factors that affect PA system speech intelligibility.
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30 Improving Intelligibility of airport terminal public address Systems ceiling height. For STI 0.60 or better, the average ceiling height was 16 feet with a range of 8 to 34 feet.
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physical Factors affecting pa Intelligibility 31 formula in that three axes are analyzed; however, it uses a different variation for combining them. Either of the latter two methods are attractive for design studies because they allow one to isolate particular room surface pairs and study design changes.
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32 Improving Intelligibility of airport terminal public address Systems of intelligibility. Studies indicate that speech intelligibility is strongly correlated to reverberation time, and, although successful examples have been identified in the literature with reverberation times up to 2.4 seconds, reducing the reverberation time below 1.9 seconds showed the strongest effect on increasing STI.
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physical Factors affecting pa Intelligibility 33 RT60 (2,000 Hz) Average Low High Arrivals 2.0 1.6 2.3 Baggage 1.5 0.6 2.8 Concourse 1.8 0.8 3.4 Food court 1.9 1.1 3.0 Gates 1.3 0.7 3.5 Ticketing 1.6 0.6 2.9 TSA 1.4 1.0 2.1 All spaces 1.6 0.6 3.4 All adequate spaces (STI 0.50 or greater)
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34 Improving Intelligibility of airport terminal public address Systems time, depending on the space and what is feasible given the size of the space. For more information, see Chapter 6.
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physical Factors affecting pa Intelligibility 35 There is a trade-off during design when deciding which materials to use and how much to use, depending on how absorptive they are. For instance, some materials are quite absorptive (e.g., 1-in.-thick acoustical panels)
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36 Improving Intelligibility of airport terminal public address Systems 4.5 Ambient and Background Noise One of the main goals in speech intelligibility is to increase the signal-to-noise ratio (SNR)
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physical Factors affecting pa Intelligibility 37 the entire group of measurements, the nighttime and daytime measurement results are not significantly different -- only 1 dBA different for the average values. Furthermore, there is a small but consistent difference in measurements between some of the terminal areas.
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From page 38... ...
38 Improving Intelligibility of airport terminal public address Systems 4.6 PA System Design One of the concepts underlying speech intelligibility is the SNR -- how does the PA system provide adequate signal to compensate for the ambient noise environment? The two primary physical factors that affect the SNR and the speech intelligibility of PA systems are reverberation time and ambient noise.
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physical Factors affecting pa Intelligibility 39 4.8 Guidance Targets Given that SNR is one of the underlying concepts for speech intelligibility, PA systems must furnish adequate signal to compensate for the ambient noise environment. Guidance values are as follows: • Design for RT60 1.1 to 1.5 seconds at 500 to 2,000 Hz to support adequate speech intelligibility of the PA system.
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