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55 This chapter focuses on the architectural design aspects of an airport and how these aspects should be addressed during the different phases of design to better ensure that the acoustical environment in which a PA system functions is conducive to intelligibility. (Key acoustical con- cepts touched on here were discussed in more detail in Chapter 4.) The aspects of the PA sys- tem design and how they interact with the architectural design are discussed briefly. Chapter 7 provides a more detailed discussion of the various elements of PA system design. An airport consists of various spaces, each having different functional requirements and often requiring different aesthetic approaches to achieve a satisfactory environment that is pleasing to airport passengers. Some airport spaces are conventional and, therefore, less challenging from an acoustical standpoint and less demanding of PA system design. In more conventional spacesâfor example, concoursesâPA system designers should be able to achieve very good intelligibility, without a lot of effort, using standard acoustical finishes and typical loudspeaker grids. Other spacesâfor example, large atriumsâare typically extremely challenging, and their special requirementsâsuch as specialized loudspeakersâmust be identified early in the design process, because the solutions available at the end of the design process may be limited or unsatisfactory. This chapterâs guidance will help designers identify when a space can be consid- ered more or less âconventionalâ and when a space needs special attention (along with what kind of attention might be required). 6.1 Key Concepts and Design Principles Six physical factors affect announcement intelligibility in an airport: 1. Room volume and shape, 2. Amount of reverberation, 3. Reflections and strong echoes, 4. Ambient and background noise, 5. PA system configuration and quality, and 6. Quality of the announcement. Of these, the first three factors (i.e., spatial characteristics, reverberation, and reflections and echoes) can be controlled through the architectural design process. The fourth factor (ambient and background noise) can be controlled to some degreeâor at least influenced byâarchitectural and mechanical design. The fifth factor (PA system configuration and quality) can be controlled during the design and installation phases. The success of the built system depends on how well each of these five factors are understood and how well a proper design is implemented. The sixth factor can be controlled, to some degree, by the airport and the airlines through staff training. Figure 6-1 illustrates how these factors relate to one another. C h a p t e r 6 Architectural Design
56 Improving Intelligibility of airport terminal public address Systems 6.1.1 Design Phases Typical architectural design follows a general progression from conceptual development to detailed construction drawings and specifications. Most building projects are divided into design phases as illustrated in Figure 6-2. Within the various design phases, guidelines for analyzing factors that affect speech intelligi- bility of PA systems are as follows: â¢ Conceptual design: â Determine the interior volume shape and character, including ceiling heights and overall visual characteristics. These will influence a roomâs acoustical response. â Flag challenging spaces (i.e., spaces with large volumes and high ceilings) for further atten- tion in schematic design. â For challenging spaces, identify the general issues involved and ascertain if acoustical and/or PA system approaches could address these issues once the design is more specific. â¢ Schematic design: â For conventional spaces, standard loudspeaker configurations and typical wall, ceiling, and floor finishes are usually available and adequate. These spaces need no special attention until design development. â Give more attention to the more challenging spaces flagged in conceptual design to con- firm that, during design development, workable acoustical and PA system solutions will be available. â Identify whether acoustical modeling will be necessary to properly design challenging spaces in design development. â Set STI goals for all spaces and identify the implications for design. â¢ Design development: â Conventional spaces: Determine room surface finishes (e.g., ceiling, walls, and floor) based on prior experience. Confirm that reverberation times will fall within normal bounds amenable to standard PA system design. Develop loudspeaker distribution and determine whether special types of loudspeakers are needed or whether ceiling-mounted cone loud- speakers in a grid pattern will be sufficient. Figure 6-1. The four physical factors that can be directly influenced by architectural design.
architectural Design 57 â Nonconventional spaces: For spaces that are large and/or have high ceilings, consider 3D acoustical modeling to more accurately evaluate the spatial acoustics and to determine optimal design tradeoffs between acoustical treatments of room surfaces and loudspeaker types and distribution. â¢ Construction documents: â Incorporate product details into drawings, specifications, and other procurement docu- ments, including performance-based requirements and specifications. â Finalize the qualifications requirements for PA system installation and commissioning. â Refer to Chapter 8 for specifics on PA system procurement. A basic background knowledge of the factors that affect intelligibility (see Chapters 3 and 4) can help in putting the above into practice. The STI design target would typically be established in conceptual design. As presented earlier in Chapter 3, the minimum guidance for speech intel- ligibility at airports is achievement of a daytime STI of 0.50, which is consistent with the NFPA 72, Annex D, guidance. However, given that STI performance is typically measured during evening or nighttime conditions, the corresponding nighttime STI target is 0.60. From this point on, only the nighttime target STI is presented. 6.1.2 Summary of Architectural and Mechanical Factors Table 6-1 summarizes the three key architectural factors and one mechanical factor and these are discussed in the following sections. (For detailed discussion about the main factors that affect intelligibility and principles for obtaining good intelligibility, refer to Chapter 4.) Figure 6-2. Typical design phases.
58 Improving Intelligibility of airport terminal public address Systems 6.2 Room Volume and Shape A room with a high ceiling (greater than 24 feet) is a challenging space to design for adequate speech intelligibility. In general, the larger the volume, the greater the distance between reflect- ing surfaces. This, in turn, affects reflections and echoes. For instance, rooms with a length greater than 5 or 6 times the width have more noticeable echoes. Figure 6-3 illustrates such a space. Figure 6-3. Ticketing hall with various shapes and surfaces. Factor Challenging conditions for speech intelligibility of PA Systems Guidance Room volume and shape High ceilings > 24 feet Long dimensions Concave surfaces Use wall-mounted or linear array speakers as ceiling- mounted loudspeakers may not be effective Provide acoustical absorption Use computer modeling Reflections and echoes Hard finishes at the end of long dimension spaces Provide acoustical absorption Reverberation Acoustical finishes Provide target amount of acoustical finishes (see Figure 4-6) Use computer modeling Ambient noise Noise source placement Noise control Use adequate buffer distances or enclosures for noisy sources Control HVAC equipment noise Reduce reverberation at noisy areas Implement adequate building sound isolation from nearby runway (See Section 6.7) PA system design High ceilings > 24 feet Consider using wall- or tower-mounted loudspeakers Table 6-1. Physical factors that affect PA system speech intelligibility that can be influenced by architectural design.
architectural Design 59 A general design principle for good room acoustics is to provide a diffuse sound field. Concave ceilings focus sound at specific points, rather than scattering sound more uniformly. Large paral- lel or flat room surfaces that are acoustically untreated can result in echoes. Carpeted floors and acoustically treated ceilings are useful for acoustics. Long volumes, such as concourses, can also present acoustical challenges, if strong reflections are allowed to propagate along the long dimension, thereby contributing to long reverberation time (RT60) or causing late echoes that are perceived as separate events. During the schematic design phase, the general shape and volume of individual terminal spaces are determined based on multiple design factors (such as program goals, design goals, expressive aspirations, budget, sustainability, constructability, and schedule). Given the gener- ous programmatic size required for many terminal functionsâsuch as ticketing, retail sales, and movement of passengers through concoursesâterminal spaces frequently require significant volume to achieve proportional balance and visual connectivity. Other programmed spaces such as security and hold rooms require more moderately scaled spaces consistent with their floor area and purpose. Coexisting within the same building, these programmatic areas present dis- tinct acoustical challenges based on size, volume, and sectional characteristics. Parallel, flat surfaces with little or no absorption can cause flutter echoes that can impede speech intelligibility. To break up flutter echoes, it can be helpful to slope one of the parallel surfaces (e.g., one of the walls or the ceiling) at a 1:11 slope. Another technique for reducing flutter echoes is to use acoustically absorptive finishes on one surface; this technique is discussed later in this chapter. Although many room shape challenges can be overcome with acoustical treatment, concave surfaces, especially ceilings, can be particularly challenging. These surfaces set up focusing pat- terns that are counter to a diffuse sound field and cause problems for PA system design. Concave surfaces must be acoustically treated to minimize these problems. 6.3 Acoustical Finishes When sound reflects off several surfaces, each reflection combines to enhance the sound. This effect is experienced as reverberation, except for strong echoes. The measure of a roomâs rever- beration characteristic is its reverberation time (RT60). For many airport public spaces where speech communication is an important consideration, an adequate design goal for airports is an RT60 of 1.1 to 1.5 seconds. Some reflection is necessary for communication in larger rooms. However, too many reflec- tions extend the reverberation time and create challenges for achieving adequate speech intelligi- bility of PA systems. A large, âacoustically hardâ surface in a space can create a strong reflection, and if the surface is a sufficient distance from the main area where speech communication is occurring, the reflection is heard as a separate event, or an echo. For airport environments, these strong, late reflections are not normally encountered. Hard-finished surfaces (such as non-carpeted floors, wall tiles, wood and metal panels, and gypsum board) all contribute to strong reflections. It is important to achieve balance with sur- faces: reflections are required to achieve a diffuse sound field, but strong reflections can be dis- tracting or cause difficulties with PA system operation. Acoustically absorptive surfaces generally need to be applied over 6% to 35% of a roomâs surfaces (e.g., floor, walls, and ceiling) to adequately reduce overall reflections and to eliminate or minimize hot spotsâareas overexposed to reflectionsâthat interfere with adequate speech
60 Improving Intelligibility of airport terminal public address Systems intelligibility of PA systems. The amount of coverage required is dependent on the total volume and the type of acoustical treatment. (Figure 6-4 illustrates this concept.) Acoustical absorption coefficients of various typical room surface finishes are listed in Appen- dix E to provide context in which to understand the relative effectiveness of different finishes as sound-absorbing materials. The noise reduction coefficient (NRC) is a single number rating that describes the absorptive properties over a range of frequencies important to speech. A value of 1.0 indicates 100% absorption while a value of 0.0 indicates 100% reflection. As discussed in Chapter 4, the amount of treated surface area and the effectiveness of that treatment in a space has an indirect relationship to the reverberation timeâas the acoustical absorption increases, the reverberation time decreases. Treating a nominal 15% to 25% of surfaces may be neces- sary to achieve a reverberation time in the range of 1.1 to 1.5 seconds or less for volumes up to 10,000 cubic feet, and 6% to 28% may be necessary for larger volumes. The distribution of these finishes can be important. The basic guidance in this document assumes a generally uniform application of absorption throughout all surfaces. Thus, the reverberation time calculation for a space where only the ceiling has been treated with acoustical absorption may be different from a calculation with the same amount of acoustical absorption uniformly applied over all surfaces (e.g., ceiling, walls, and floor). For complex or large spaces, or for challenging designs, it may be essential to enlist the services of an acoustical consultant. For simple configurations, uniform distribution of the acoustical material across all surfaces is ideal. 6.3.1 Ceilings Many ceiling finish options are available for airports, including â¢ Acoustically absorptive perforated panels â¢ Gypsum board â¢ Acoustically absorptive cementitious panels â¢ Acoustically absorptive spray-applied plaster â¢ Acoustical ceiling tiles (ACT) â¢ Stretched fabric, which is used as a finish to cover acoustical absorption for complex ceiling shapes The NRC value of these materials typically ranges from 0.40 to 0.90. When ceiling and floor are both flat, a strong echo can occur between the two, which is counter to providing adequate speech Figure 6-4. Gate hold area with acoustical ceiling tile and carpet.
architectural Design 61 intelligibility of PA systems. To reduce the strong echo, it may be adequate to treat (either the floor or the ceiling). Treating both surfaces distributes the absorption and thus allows more flexibility with ceiling finish selection. Sloping the ceiling is another option, as discussed in Section 6.2. 6.3.2 Walls Similar to the relationship between ceilings and floors described above, if opposing walls are flat, strong echoes can occur, and use of acoustical panels or similar treatments may be one way to improve the room acoustics. In some areas, such as a series of gate hold rooms with a low ceilingâ less than 12 feet highâthe long space between the parallel âendâ walls is broken up with furniture or other large objects that also reduce the flutter effect. However, in a space with acoustically hard floors and ceilings, the wall surfaces and furniture offer the only remaining option for controlling reverberant sound. 6.3.3 Floors It is critical to address terminal building circulation zones, given the hard floor surfaces in these areas. In some areas of the airport, carpet is an option (e.g., in gate hold rooms). The main circulation areas are typically finished with an easy-to-maintain and durable surface (e.g., ter- razzo tile or sealed concrete). If carpet is installed, it is either glue-down carpet tiles or wall-to-wall carpeting. For cleaning and maintenance reasons, the carpet tends to be low pile or outdoor grade, which provides only 0.30 NRC. When ceiling and floor are both flat, a strong echo can occur between the two, which is counter to providing adequate speech intelligibility of PA systems. Two reasons to consider using a carpet are as follows: â¢ All passengers traverse the floor, and passengers generate more background noise on a hard floor surface. â¢ Where there is a dramatic ceiling design, it may be difficult to integrate an adequate acousti- cally absorptive treatment using hard floor surfaces. 6.4 Acoustical Considerations by Terminal Functional Area Various terminal areas serve different functions. Consequently, the architectural and acousti- cal considerations are different for each area. The needs of the PA system also vary, depending on the function. This section discusses areas describing physical challenges and how the function of space affects PA announcements. These spaces are divided into two types: exterior and interior. Airport exterior spaces are often limited to curbside areas (arrivals and departures). Interior spaces include ticketing, TSA security checkpoints, gates areas, concessions, baggage claim, and arrivals and departures halls. Table 6-2 summarizes the design elements relevant to interior spaces. The only exterior space at airports where PA systems are used is the curbside area. Table 6-3 summarizes the two design challenges relevant to this space. 6.5 Concept of Acoustically Distinguishable Space (ADS) Terminal spaces served by the PA system can vary in size and shape from relatively small (<5000 cubic feet) to very large (>>500,000 cubic feet) to very long (length >5 times width). A useful concept to keep in mind when identifying these spaces is the concept of an acoustically distinguishable space (ADS), which is defined in NFPA 72 as a space that is âdistinguished from
62 Improving Intelligibility of airport terminal public address Systems other spaces due to acoustical, environmental or use characteristics, such as reverberation time and ambient sound pressure level.â ADS is a subjective concept, in part based on understanding the physical factors at play; there are no hard and fast rules in defining an actual ADS. Figure 6-5 illustrates how an ADS might be determined. A building has boundaries defined by the exterior shell (such as walls, windows, doors, and roof). Many rooms also have clear boundaries, defined by walls and a door. In airports, there also are well-defined rooms and well-defined spaces; in many cases, the definition of the space might be based on a boundary where there is no wall. The concept of ADS is general: a space that mea- sures 12 ft high by 100 ft long by 50 ft wide is probably acoustically similar to an adjacent space measuring 10 ft high by 80 ft long by 55 ft wide. The addition or lack of acoustical absorption from one space to another (e.g., carpet in a gate hold area and tile in the lobby) can be enough to distinguish the two as separate ADSs. Commonalities can be found in gate hold areas, baggage claim areas, ticketing halls, gate counters, and concession areas, which have similar reverberant and ambient sound conditions. Figure 6-6 shows such a space. Challenge Thresholds Guidance Ambient noise High â¥65 dBA Select horns or column array loudspeakers Reverberation time at lower levels 1.1 to 1.5 seconds <10,000 square feet treat 15 to 35% SA >10,000 square feet treat 6 to 28% SA Table 6-3. Summary of design considerations for exterior spaces. Challenge/Condition Thresholds Guidance Ceiling height Moderate >13 feet Be aware of increased challenges for speech intelligibility beyond basic PA system design High >24 feet Consider wall-mounted or column array loudspeakers as ceiling-mounted loudspeakers might not be viable; Use design professionals for acoustics and PA system design Reverberation time 1.1 to 1.5 seconds Treat 15 to 35% SA for <10,000 square feet; Treat 6 to 28% SA for >10,000 square feet Ambient noise Moderate >59 dBA High â¥65 dBA Apply acoustical treatment and noise controls Use design professionals for acoustics and A/V consultant for PA system design Strong echoes Large reflective surfaces more than 100 feet away from an ADS Large parallel surfaces Use acoustical absorption if required to minimize echo Use acoustical absorption on one surface or taper one surface 1:11 Concave surfaces Any Use acoustical absorption on the concave surface Consider wall-mounted or column array loudspeakers PA loudspeaker placement High ceiling >24 feet Consider wall-mounted or column array loudspeakers Use design professionals for acoustics and PA system design SA: surface area Table 6-2. Summary of design considerations for interior spaces.
architectural Design 63 A series of spaces, such as gate hold rooms, could be considered one ADS because they share the same ceiling height and width, furnishings, and other acoustical characteristics (exceptions may be gate areas that have different environmental conditionsâfor example, one or more areas are closer to a restaurant or bar or near noisy HVAC equipment). The concourse or walkway next to these gate hold areas, on the other hand, would probably constitute a different ADS, given a higher ceiling, an acoustically hard floor finish, and a different PA system layout. Fig- ure 6-7 shows such a space. 6.6 Ambient and Background Noise Considerations for Interior Spaces PA announcement levels are typically set to be about 72 dBA at the height of a typical standing passenger. To meet the guidance target (10 to 15 dBA SNR), the background noise level should be 59 dBA, because this is essential for adequate speech intelligibility of PA systems. Ambient noise-sensing microphones can help adjust the PA signal to account for increases in ambient noise conditions; if an ambient noise-sensing system will be specified for the PA system, it will only be necessary to design for the typical, ongoing environment. Other basic guidance for con- trolling ambient noise sources includes providing â¢ Adequate buffer distances or enclosures for mechanical equipment, escalators, concessions areas, and similar noise sources. â¢ Adequate isolation at gate areas from exterior noise coming from passenger boarding bridges. Figure 6-5. Schematic illustration of an ADS. Figure 6-6. Ticketing hallâlong, low room.
64 Improving Intelligibility of airport terminal public address Systems 6.6.1 Mechanical Equipment Background noise caused by mechanical equipment is generally the easiest type of noise to control. The most common examples of noise-generating mechanical equipment in terminals are the HVAC system (the base building system and tenant improvements), escalators, moving walkways, elevators, baggage carousels, baggage conveyors, and concessions refrigeration equip- ment. To achieve target quiet ambient noise levels of 59 dBA or less, the HVAC system itself must typically be designed for 50 to 55 dBA or less. Noise criteria (NC) level guidance is adapted from ASHRAE (ASHRAE 2011), where NC 40 is used for lobbies and corridors. NC 45 typically corresponds to a 50 to 53 dBA background sound level; in a space where HVAC equipment is the dominant noise source, the equipment defines the quiet ambient sound level. Table 6-4 provides guidance about industry practice for controlling this type of equipment. 6.6.2 Airport Passengers The sound generated by passengers contributes to the ambient noise. The main challenge from an acoustical design standpoint is the variability of this noise level due to the constantly changing number of passengers present at any one time and changes in their levels of activity. A hard floor reinforces the sounds that passengers make when walking and rolling luggage along the floor. Highly reverberant room conditions also strengthen the sound of passenger voices. A room with high reverberation tends to encourage people to talk louder, because the din makes people feel Figure 6-7. Ticketing hall with high, sloping ceiling. Space Design Goal Typical Sound Level Equivalent Comment Concourse and circulation NC 45 50 to 53 dBA Consider vibration isolation for the fans and ductwork Baggage claim NC 45 to 50 50 to 58 dBA Strive for NC 45 if possible Arrivals and ticketing NC 45 50 to 53 dBA Consider vibration isolation for the fans and ductwork Hold rooms/lounges NC 40 45 to 48 dBA Use vibration isolation for the fans and ductwork Moving walkways, baggage claim belts NC 60 at a 3-foot distance from motors and noise sources 65 to 68 dBA Provide a higher level of acoustical absorption in the 8-to-12-foot area nearest the source to control the reverberant sound Table 6-4. Typical design goals for HVAC and mechanical equipment in public spaces.
architectural Design 65 they must speak more loudly or yell to be heard. Three basic options to mitigate these issues are (1) design of walls or structures to contain or limit noise from passengers, (2) establishment of a buffer distance between noisy passenger spaces (e.g., a sports bar) and noise-sensitive areas (e.g., a gate hold area), and (3) use of acoustical absorption to reduce reverberant buildup. Events at U.S. airports in August 2016 underscore the importance of controlling ambient noise. In two separate events, at two different airports, unidentified loud noises inside the termi- nal led to speculation that guns were fired. In the first case, the noise was caused by cheering from people watching the Olympic Games. In the second case, an unidentified noise was mistakenly linked to gunfire. In both cases, the confusion caused concern and panic. 6.6.3 Airport TV Monitors TV monitors are in many places in airports, particularly gate hold areas and concessions courts. Some airports have chosen to silence TVs and use closed captioning, while other airports have chosen to play TV audio at a low level. However, in some of these cases, the volume of the TV audio is high enough to interfere with PA system announcements. (This situation can be particularly frustrating when it appears that no one is actually watching or listening to the TV broadcast.) These televisions are usually not interlocked or interfaced with the PA system, so when announcements are made, the speech intelligibility of the PA system is reduced because the TV audio interferes with it. Placement of TVs requires coordination with the tenant/operator to minimize intrusion in passenger areas and maximize the speech intelligibility of the PA system. 6.6.4 Competing PA Announcements Simultaneous announcements made in adjacent spaces are another source of competing noise for individual announcements. Typically, airport PA systems are designed to keep this from hap- pening by interlocking announcements so that two gate agents cannot make announcements in the same zone at the same time. Sometimes the issue is that the loudspeakers from two different zones are too close together (see Figure 6-8). The resolution of these problems is largely in the scope of PA system design and PA system operations and training. During the architectural design process, it may be possible to increase the acoustical isolation between close spaces using furniture or a high level of acoustical absorption (e.g., NRC >0.8, }25% coverage). Figure 6-8. Adjacent gate waiting areas.
66 Improving Intelligibility of airport terminal public address Systems 6.6.5 Background Music Most airports avoid playing background music; however, some airports play music in cer- tain areas and/or under certain circumstances. Typically, background music is linked to the PA system, so that the music is paused or muted during PA system announcements. If this is not the case, the speech intelligibility of the PA system is reduced, because the background music interferes with PA announcements as discussed in Chapter 5. In attempts to improve passenger experience, some airports have introduced live music in selected areas. Programs can range from a quiet soloist to a full band (e.g., eight-piece band or combo). PA announcements in these areas can be affected by competition from the perfor- mance. Thoughtful design can limit the zone of influence of such eventsâfor example, by including barriers or walls to minimize the noise impact of the performance on adjacent public areas and ensuring a high level of acoustical absorption (e.g., NRC >0.8, }25% cover- age) in the performance area, as well as addressing the particular requirements of the PA system in such circumstances. 6.6.6 Passenger Boarding Bridges Sound from passenger boarding bridges is generally not a significant factor in PA system intelligibility, and most boarding bridges do not have loudspeakers. However, it may be useful to consider how to minimize jet engine noise transfer into the gate area via the bridge, because this noise increases the background noise and affects the intelligibility of announcements in the gate area. Adding a high level of acoustical absorption to the 8-to-12-foot area immediately next to the bridge access door can help contain noise in that immediate area. In an emergency, airports have processes to direct passengers off the boarding bridge and so do not have to rely on PA announcements in the passenger boarding bridges. 6.6.7 Electric Passenger Transport Carts Electric transport carts are generally quiet relative to other sources of background noise. Further more, the little noise they generate is only momentary in any one location. The reverse backup alarm is highly audible, for obvious reasons, but these alarms are seldom used near gate hold areas and hence probably are not a major source of noise. At facilities that have higher- than-average use of these carts, airport spaces should be designed to avoid the need for backup maneuvers (e.g., by increasing corridor width to allow for vehicle-turning radius). 6.6.8 Interterminal Automated People Movers (APMs) Larger airports often have APM systems running between terminal buildings. These systems can either be outdoors or underground. In some airports, the APM is within the concourse of the terminal building. Shuttle vehicles themselves generate noise, but the platform waiting areas typically have automated doors that close when the shuttle enters and leaves the station. These doors tend to minimize the shuttle vehicle-generated noise (e.g., vehicle HVAC) heard by wait- ing passengers. 6.6.9 Aircraft Noise at the Terminal At some airports, noise from small jet and propeller airplanes approaching the terminal, as well as more distant noise from airplanes taking off or landing on runways, is not sufficiently addressed by the terminal building shell (this is particularly true for small plane operations on
architectural Design 67 the tarmac when the exit doors are open during passenger embarkation and debarkation). If the exterior shell is not adequate to control such noise sources, exterior noise can greatly affect the ambient noise conditions in the airport and influence PA system speech intelligibility (e.g., in gate hold areas). Nominal OITC 40/STC 55 for walls and windows in a terminal building next to a runway may be needed in order to reduce this aircraft noise, which has been documented to reach 65 to 70 dBA inside a modern airport. 6.6.10 Concession Areas Retail kiosks may have their own audio systems that contribute to background noise, although the music from such systems would typically be localized to the immediate vicinity of the kiosks. The base building design can consider the added noise sources for planned areas. Food courts can be a source of background noise, depending on how fully occupied they are. In addition, the flooring in food court areas is normally acoustically hard for ease of mainte- nance, and the ceiling height may be moderate or high (see Figure 6-9). The most effective ways to minimize the effects of food court noise on the speech intelligibility of PA systems are to â¢ Apply as much acoustical absorption as possible, so that the noise is not enhanced more than necessary. â¢ Select furniture that minimizes unnecessary noise from chairs scraping on the floor. 6.7 Ambient and Background Noise Considerations for Exterior Spaces Motor vehicle noise at the curbside is likely to be a substantial contributor to the ambient noise level at the curbside, particularly if the roadway is partially enclosed, in which case the noise would reflect from overhead roadway decks and terminal exteriors and, in some cases, nearby parking structures. Ambient noise levels in these areas can easily be higher than announcement levels. Therefore, vehicle noise needs to be considered in the design of the curbside area (see Figure 6-10). Figure 6-9. Food concession area.
68 Improving Intelligibility of airport terminal public address Systems To support a successful PA system design, it is essential to reduce reflection conditions in the curbside area; in semi-enclosed conditions, it may be necessary to consider reverberation. This typically entails the use of cementitious or other exterior-grade acoustically absorptive treatment to the exterior finish and possibly to the underside of roadway decks or similar hard surfaces above the curbside area. 6.8 Airport Size Considerations Although larger airports tend to have more acoustically complex spaces and are more heavily traveled, many terminal spaces (e.g., gate hold rooms, restrooms, and TSA security checkpoints) are similar, regardless of the size of the airport; consequently, the design challenges are similar. From the standpoint of speech intelligibility for PA systems, design considerations are the same for all spaces, regardless of airport size. 6.9 Sustainability Considerations Many resources offer information about sustainable design as it relates to architectural finishes and materials. Many eco-friendly acoustical products are available that use recycled materials and materials with low off-gassing. Renovation projects may require replacement of a consider- able quantity of wallboard, metal, wiring, and electronics; some amount of this can be recycled. Many organizations have addressed the management of sustainable materials in architectural projects. The EPA provides procurement guidelines for construction products (see https://www. epa.gov/smm/comprehensive-procurement-guidelines-construction-products). Chapter 7 pro- vides information about electronics and sustainability. 6.10 Computer Modeling Software for Acoustical Design This section discusses the benefits and limitations of computer programs that can be used to model the acoustic environment of common, as well as unusual, terminal spaces. With such modeling tools, it is possible to quantitatively determine speech intelligibility in the presence of Figure 6-10. Curbside area with deep overhang and a high ceiling.
architectural Design 69 background noise for several representative locations (i.e., ADSs) within an enclosed terminal space, thus optimizing loudspeaker type, configuration, and placement. Several commercially available software packages include both acoustical design and PA system design to estimate the speech intelligibility of the combined designs. Chapter 7 presents more information about necessary program features. In general, with the guidance presented in this chapter, simple spaces with ceiling heights of 12 feet and lower could be designed for the target speech intelligibility [STI 0.50 for daytime (wet) conditions], and ceiling heights up to 24 feet could be adequately addressed with best- practice guidance, although an outside acoustical consultant would be helpful in identifying challenging conditions. Design of complex spaces and spaces with ceiling heights greater than 24 feet would benefit from an acoustical consultant who can evaluate basic speech intelligibility using various room acoustics computer packages that include a simple PA system module. The key properties of any 3-D software package are as follows: â¢ A ray-tracing algorithm, which is essential to model a complex space (because it may be important to know the specific placement of acoustical treatment); â¢ The ability to calculate the STI from the PA system, including the capability to model loud- speakers in the ceilings, on the walls, and in linear arrays; â¢ The ability to calculate the RT60 (for complex spaces, the program should include several dif- ferent algorithms, including those developed by Sabine, Fitzroy, and Arau-Puchades); and â¢ The option to factor air absorption into design calculations in addition to the room finishesâ this is useful for complex spaces where the reverberation time is difficult to control. A computer model is only one of the tools in the PA designerâs toolkitâcomputer models are not a substitute for the PA designerâs skill and experience. A PA system designer must use professional judgment when determining how to apply a computer model and how to interpret the results of the modeling to predict PA system performance.