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155 Acoustics The acoustic environment within and around airport terminal buildings can affect the pas- senger, employee, and visitor experience. Unintelligible PA announcements increase passenger stress levels. Reverberation, Transmission, and Equipment Noise Criteria The Authority encourages all project design teams to employ a building acoustics specialist to review key acoustical characteristics of spaces and building systems. This review might range from a complex calculation of reverberation time for large, complex passenger processing spaces to a simple review of a wall assembly to reduce sound transmission between adjacent spaces. The following considerations shall be addressed for each project: â¢ Reverberation: Various factors (e.g., volume, shape, and the quantity and location of sound- absorbing or sound reflecting materials) contribute to the acoustical character of a space. These factors affect the reverberation time (RT60) of the space. Undesirable sound reflections can create an uncomfortable environment acoustically and decrease speech intelligibility. âFlutter echoâ is an undesirable reflection caused by parallel reflecting surfaces. Consider sound-absorbing finishes to reduce reverberation time, especially at the 500 to 2,000 Hz range where speech occurs. For optimal paging system performance, reverberation time should be 1.5 seconds or less, and preferably less than 1.1 seconds for critical spaces served by PA systems. Consider appropriate surfaces for sound-absorbing materials, with regard to durability and maintainability. â¢ Transmission: Noise transmission through ceilings, walls, windows, doors, and floors between adjacent spaces shall be analyzed. Strategies such as mass loading, sound isolation, and avoiding flanking noise pathways shall be considered. Required ambient noise levels based on function of the spaces shall determine the type of construction needed. Note these criteria in the Project Definition Document and specifically note recommendations for any deviations from requirements â¢ Equipment Noise: Noise and vibration data shall be provided for equipment such as air handling units, pumps, drives, variable air volume units, fan-powered boxes, cooling towers, chillers, and baggage conveyors. Vibration isolators, acoustical liners, duct sound traps, and fan speeds shall be considered and equipment shall be acoustically isolated from adjacent spaces as noted in the preceding transmission paragraph. In addition, in public spaces, plumb- ing noise (specifically that from roof top rain leaders) shall be assessed and controlled, if necessary. A p p e n d i x H Sample Design Criteria Elements Relevant to Speech Intelligibility
156 improving intelligibility of Airport Terminal public Address Systems Noise Criteria (NC) Recommendations The following are design criteria targets for noise levels that shall be addressed in the initial project documentation and Basis of Project Definition Document. This is not a comprehensive list of all interior spaces in a terminal or other airport facilities. These criteria are adapted from the ASHRAE guidelines for public spaces such as corridors and lobbies (2011 ASHRAE Handbookâ HVAC Applications, Chapter 48, Noise and Vibration Control). Designers shall recommend cri- teria for spaces not listed below and note them in the Project Definition Document. â¢ Gate hold areas/Lounges: Many people use their time in a lounge to make phone calls and, if noise levels are too low, these are easily overheard. The same applies to general conversations. Therefore, it is recommended that the noise limit of NC 40 be adopted. â¢ Concourses and Circulation Spaces: NC 45 is recommended. â¢ Baggage Claim: NC 45 to 50 is recommended. â¢ Arrivals and Ticketing Hall: NC 45 is recommended. â¢ Moving Walkways and Baggage Claim Belts: A noise limit of NC 60 at 3 feet. PA System Intelligibility Speech intelligibility, a quality distinct from audibility, relates to the potential ability of lis- teners to understand the messages delivered (not including language and contextual factors). Audibility is only a component of intelligibility, as can be demonstrated by experiences in large, hard-finished public spaces where an announcement can be heard, but the message content cannot be distinguished. In building terms, major factors affecting the speech intelligibility of a PA system are â¢ The sound level of the system relative to the background noise levels (âsignal-to-noise ratioâ) â¢ The acoustic response of the space and, hence, the level of âusefulâ sound received directly from the loudspeakers relative to the delayed reverberant sound (âdirect-to-reverberant ratioâ). Despite this objective approach to understanding the salient mechanisms, speech intelligibil- ity remains a subjective quality that will be judged differently by each listener and for different messages and/or talkers. For design purposes, some objective measures are available, includ- ing the Speech Transmission Index (STI) that is often measured using the STIPA method. STI is an index from 0.0 to 1.0, with higher numbers representing higher intelligibility. Interna- tional standards relating to PA systems for emergency purposes state a typical requirement for STI of 0.5. However, the standards allow for the objective nature and for lower STI ratings in response to practical constraints. Overhead loudspeakers probably will not be viable in areas with a floor-to-ceiling heights of more than 24 feet. Loudspeakers will probably need to be integrated into floor features (e.g., services pods and FIDS supports). This approach can provide good sound coverage and intel- ligibility and would enable specific loudspeaker zones to be defined by partitions. However, the relocation of large objects such as retail units could result in acoustic shadow zones being created that would need additional fill in loudspeakers. Limitations on the âthrowâ distance for loudspeakers dictate a minimum spacing of around 45 feet. Note acoustical requirements in other sections of these standards.