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1 S u m m a r y ACRP Research Report 175: Improving Intelligibility of Airport Terminal Public Address Sys- tems presents guidelines developed to help airports and their consultants design, procure, install, operate, and maintain PA systems adequate for both communication and safety. The report also addresses training needs for personnel involved with PA systems. Although many of the acoustical concepts are well-studied and readily applied from other public spaces, such as transportation hubs (for example, subway stations and railway terminals) and shopping centers, the challenges and elements at airports (for example, room shapes, ambient noise sources, multiple languages, security concerns, multiple operators, and schedules) combine to form a unique environment. The research team conducted a literature review, took field measurements at airports, admin- istered an online questionnaire to assess industry perceptions on this topic, and developed a pilot passenger survey on how airports can conduct their own research on human factors issues specific to their airports. The research team developed the questionnaire to collect information from the airport industry on how the industry understands factors involved in speech intelligibility and whether respondents consider intelligibility a widespread problem. Given that the passenger experience may differ from that of staff and crew in the airport and to understand how data might be collected from passengers, the pilot passenger survey was conducted at one airport. Many airports seek professional design services for new projects and extensive renovation projects; the importance of parameters such as room volume and shape, surface finishes, and noise control is not always clear during the design process. PA systems are sometimes updated or replaced without awareness that room acoustics and ambient noise conditions are vital to the success of a PA system. The guidelines in this report clarify how design can establish condi- tions for satisfactory PA system performance and how a PA system can be optimized for best performance, given actual acoustical conditions. Following are the main guidelines for improving speech intelligibility: â¢ Use a Speech Transmission Index (STI) 0.60 performance target to compensate for the typi- cal difference in the ambient condition between performance testing and normal operations. â¢ Ensure that acoustically absorptive treatment is adequate (nominally 15% to 25% of sur- face area)âproper reverberation time is critical to speech intelligibility. â¢ For spaces with ceiling heights higher than 24 feet, get professional input for acoustics and PA system design; ceiling-mounted loudspeakers are generally discouraged for these types of spaces. â¢ Ensure that the PA system provides at least 10 to 15 dB signal-to-noise ratio (SNR) in the presence of typical daytime ambient noise conditions. â¢ Prepare announcements so as to take advantage of human response to broadcast information. â¢ Require commissioning to verify and optimize the PA system prior to sign-off or acceptance. Improving Intelligibility of Airport Terminal Public Address Systems