Improving Intelligibility of Airport Terminal Public Address Systems (2017)

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105 This chapter cross-references key tables and figures provided in the guidelines. Application examples are included here to illustrate how problems can be minimized at various steps of the design process. 12.1 Quick Reference for Guidance Tables and Charts Architectural Design Guidelines See Figure 4-6. Nominal percentage surface area necessary to achieve RT60 less than 1.5 seconds See Table 1-1. Project timing chart for physical factors that affect PA system speech intelligibility See Table 6-1. Physical factors that affect PA system speech intelligibility that can be influ- enced by architectural design See Table 6-2. Summary of design considerations for interior spaces See Table 6-3. Summary of design considerations for exterior spaces See Section 6.7 Ambient and Background Noise Considerations for Exterior Spaces Mechanical Equipment Design Guidelines See Table 6-4. Typical design goals for HVAC and mechanical equipment in public spaces PA System Design Guidelines See Table 7-1. Loudspeaker types and beneficial configurations See Table 7-2. Guidance summary for PA system design Commissioning Tests See Figure 9-1. Steps in commissioning a PA system. See Section 9.4.5 Troubleshooting the Speech Intelligibility of the PA System Installation Announcement Guidelines See Figure 10-1. Announcement information example. 12.2 Examples from Field Measurements Following are nine examples taken from the research. During the field measurements, the research team “walked” each ADS to sample the one-third octave band spectrum once per sec- ond. Thus, some samples were taken on-axis under a loudspeaker and some were taken between loudspeakers. The uniformity of sound coverage can be represented graphically from this data. The data was measured using pink noise at a level necessary for good acoustical SNR. If it took C h a p t e r 1 2 Decision Tools and Examples

106 Improving Intelligibility of airport terminal public address Systems 30 seconds to walk the space, for example, there are 30 curves in that ADS plot. For each example in this section, a range of values illustrating the “PA System Target Uniformity” is included. The measured uniformity printed at the top of the plot is the range of A-weighted values for all the curves in that ADS. A “target uniformity” range is shown on each plot, centered on the average of the 1,250 Hz one-third octave band values. This target range indicates a typical frequency response optimized for speech intelligibility and natural sound, not music reproduction. The plots show frequency- specific uniformity and do not imply PA system sound level performance. These plots are use- ful to evaluate issues that affect speech intelligibility. Figure 12-1 shows such a plot. For each example, a sample of the ambient noise level at the time of the measurement is shown in each figure as a reference. Figure 12-1. Sample PA system uniformity graph.

Example 1 Design Overcomes Very Challenging Conditions to Achieve STI 0.49 Description: Large Concessions Space Year commissioned: 2005 (Upgrade to digital system in 2015) TechnicAl DATA Daytime ambient noise level 64 dBA Leq Announcement SPL 72 dBA Leq Nighttime ambient noise level 59 dBA Leq STI range 0.46 to 0.49 Uniformity ± 4 dBA Reverberation time (RT60) 2.7 sec at 500 Hz 2.9 sec at 2,000 Hz ArchiTecTurAl/AcouSTicAl DeTAilS Ceiling height 59 feet Finishes Perforated metal ceiling, terrazzo floor, glass wall/window at perimeter PA SySTem DeTAilS PA system type Digital Paging microphone type Omnidirectional push talk Loudspeaker type Ceiling- and fascia-mounted loudspeakers around perimeter; steerable column array at one end (by video monitor); one frontal loudspeaker at opposite end Loudspeaker spacing 31 feet (ceiling-mounted loudspeaker spacing) Ambient sensing microphones Yes SPeech inTelligibiliTy DiScuSSion The speech intelligibility at this space could be improved, but it performs remarkably well considering the challenging factors, including: • Room acoustics. This is a very reverberant space at > 2 seconds. • High ambient/background noise. The nighttime ambient noise level of 59 dBA is on par with the higher range of conditions measured; likewise, the daytime ambient noise level of 64 dBA was consistent with the higher range measured at all locations. Daytime noise sources include food court activity, dishes, HVAC, and background music. • Loudspeaker layout. The ceiling is high—well above the 24-ft guidance for ceiling-mounted loudspeakers— and the spacing was larger than 20 feet. The column array and frontal loudspeaker help improve speech intelligibility. WhAT cAn be imProveD • Room acoustics: Incorporate acoustical absorption to reduce the RT60 as close as possible to 1.5 seconds or less. This will reduce some of the daytime ambient noise and reduce noise from announcements at nearby gates. (See Chapter 6 re architectural design.) • High ambient noise: – Incorporate noise control to reduce background sound from the HVAC system; NC 45 or lower. (See Chapter 6 re architectural design.) – Incorporate interconnect with background music to mute music during announcements. (See Chapter 5 re human factors.) • Loudspeakers and PA system design: – Replace ceiling-mounted loudspeakers with more column arrays. This might not be practical for such a new system. (See Chapter 7 re PA system design.) – Improve PA system EQ. (See the testing and commissioning procedures discussed in Chapters 8 and 9.) – Improve uniformity of PA sound coverage. (See the testing and commissioning procedures discussed in Chapters 8 and 9.)

108 Improving Intelligibility of airport terminal public address Systems (a) Large concessions space. (b) Measured PA system uniformity and frequency response.

Decision tools and examples 109 Example 2 High-Performance Ceiling Treatment Provides STI 0.65 in High Ceiling Space Description: Concessions, Food Court Year commissioned: 2011 TechnicAl DATA Daytime ambient noise level 62 dBA Leq Announcement SPL 73 dBA Leq Nighttime ambient noise level 52 dBA Leq STI range 0.62 to 0.69 Uniformity ± 1 dBA Reverberation time (RT60) 1.1 sec at 500 Hz 1.1 sec at 2,000 Hz ArchiTecTurAl/AcouSTicAl DeTAilS Ceiling height 30–38 feet Finishes Terrazzo floor, acoustical ceiling tile, gypsum board interior finishes PA SySTem DeTAilS PA system type Digital Paging microphone type Omnidirectional push talk Loudspeaker type Ceiling-mounted loudspeakers Loudspeaker spacing 28–36 feet (ceiling-mounted loudspeaker spacing) Ambient-noise-sensing microphones Yes SPeech inTelligibiliTy DiScuSSion Excellent PA system sound coverage and high speech intelligibility, largely due to controlled reverberation. Challenging conditions include • Large-volume space with high ceiling and tile floor. • Localized background noise from food court mechanical equipment (e.g., refrigeration equipment). • PA system frequency response is relatively flat except for mid-low “bump” at 400 Hz that tends to mask intelligibility at higher speech frequencies. WhAT cAn be imProveD • Room acoustics: none. High-NRC ceiling tiles already in use. • High ambient noise: Incorporate noise control to reduce background sound from the HVAC system; NC 45 or lower. (See Chapter 6 re architectural design.) • Loudspeakers and PA system design: Improve PA system EQ per testing and commissioning procedures discussed in Chapters 8 and 9.

(a) Concessions area. Photo Credit: Wilson Ihrig (b) Measured PA system uniformity and frequency response.

Decision tools and examples 111 Example 3 Average Performing ADS with Room for Improvement Achieves STC 0.49 Description: Ticketing Year commissioned: 2011 TechnicAl DATA Daytime ambient noise level 62 dBA Leq Announcement SPL 70 dBA Leq Nighttime ambient noise level 52 dBA Leq STI range 0.47–0.52 Uniformity ± 1 dBA Reverberation Time (RT60) 1.0 sec at 500 Hz 0.9 sec at 2,000 Hz ArchiTecTurAl/AcouSTicAl DeTAilS Ceiling height 18–20 feet Finishes Carpeting in cue area, terrazzo floor adjacent; angled ceiling of micro- perforated metal panel with faux wood finish; glass exterior wall; gypsum board and metal panel interior; and ventilation diffusor walls. PA SySTem DeTAilS PA system type Digital Paging microphone type Omnidirectional push talk Loudspeaker type Ceiling-mounted loudspeakers; Loudspeaker spacing 12–17 feet (ceiling-mounted loudspeaker spacing) Ambient-sensing microphones Yes SPeech inTelligibiliTy DiScuSSion Many positive attributes in this space, including PA system uniformity, but the speech intelligibility can be improved. Challenging conditions include • Large areas of acoustically hard surfaces. • Background noise. • PA system frequency response is relatively flat except for mid-low “bump” at 200 Hz that tends to mask intelligibility at higher speech frequencies. WhAT cAn be imProveD • Room acoustics: None. • High ambient noise: Incorporate noise control to reduce background sound from the HVAC system; NC 45 or lower. (See Chapter 6 re architectural design.) • Loudspeakers and PA system design: Improve PA system EQ per testing and commissioning procedures discussed in Chapters 8 and 9.

(a) Ticketing area. Photo Credit: Wilson Ihrig (b) Measured PA system uniformity and frequency response.

Decision tools and examples 113 Example 4 Low-Ceiling Space Underperforms at STI 0.32 Description: Baggage claim area Year commissioned: unavailable TechnicAl DATA Daytime ambient noise level 62 dBA Leq Announcement SPL 70 dBA Leq Nighttime ambient noise level 62 dBA Leq STI range 0.32 Uniformity ± 1 dBA Reverberation Time (RT60) 2.9 sec at 500 Hz 2.8 sec at 2,000 Hz ArchiTecTurAl/AcouSTicAl DeTAilS Ceiling height 8–13 feet Finishes Arched plaster ceiling, terrazzo floor. No acoustical treatment. PA SySTem DeTAilS PA system type Digital Paging microphone type N/A Loudspeaker type Ceiling mounted Loudspeaker spacing unknown Ambient-noise-sensing microphones No SPeech inTelligibiliTy DiScuSSion This space is in the same airport as the previous example. In this case, the low ceiling cannot overcome poor acoustical environment. Challenging conditions include • Acoustically hard surfaces • Long reverberation time • Adverse reflections from the ceiling • High ambient noise from HVAC • PA system frequency response is not smooth, with a “bump” at 250 Hz that can distort the sound. WhAT cAn be imProveD • Room acoustics: Substantial benefits to be gained from increasing the acoustical absorption to reduce the reverberation time and reduce strong reflections from the ceiling. Incorporate acoustical absorption to reduce the RT60 as close as possible to 1.5 seconds or less. This will also reduce some of the daytime ambient noise. (See Chapter 6 re architectural design.) • High ambient noise: Incorporate noise control to reduce background sound from the HVAC system. NC 45 or lower. (See Chapter 6 re architectural design.) • Loudspeakers and PA system design: Improve PA system EQ per testing and commissioning procedures discussed in Chapters 8 and 9.

(a) Baggage claim area. Photo Credit: Wilson Ihrig (b) Measured PA system uniformity and frequency response.

Decision tools and examples 115 Example 5 Quiet Ambient and Basic Good Design Achieves STI 0.73 (dry)/0.46 (wet) Description: Baggage claim area Year commissioned: 2004/2008 TechnicAl DATA Daytime ambient noise level 61 dBA Leq Announcement SPL 67 dBA Leq Nighttime ambient noise level 47 dBA Leq STI range 0.73 Uniformity ± 2 dBA Reverberation Time (RT60) 0.8 sec at 500 Hz 0.9 sec at 2,000 Hz ArchiTecTurAl/AcouSTicAl DeTAilS Ceiling height 19 feet Finishes Terrazzo floor; metal-slat suspended ceiling; glass exterior wall. PA SySTem DeTAilS PA system type Digital Paging microphone type N/A Loudspeaker type wall mounted at 14.5 feet height Loudspeaker spacing 21 feet Ambient sensing microphones Yes SPeech inTelligibiliTy DiScuSSion Nighttime ambient conditions are extremely low, which partially accounts for the exemplary STI result. However, daytime conditions lower the STI to a 0.46. Challenging conditions include • Strong reflections from glass wall • Moderate ambient noise from HVAC • PA system frequency response is not smooth, with strong high-frequency response which possibly contributes to the high STI • Low announcement signal level WhAT cAn be imProveD • Room acoustics: Despite low reverberation time, some benefits can be gained from reducing strong echoes off glass wall and metal slats. (See Chapter 6 re architectural design.) • High ambient noise: Incorporate noise control to reduce background sound from the HVAC system. NC 45 or lower. (See Chapter 6 re architectural design.) • Loudspeakers and PA system design: Improve PA system EQ per testing and commissioning procedures discussed in Chapters 8 and 9.

Photo credit: Wilson Ihrig (a) Baggage claim. (b) Measured PA system uniformity and frequency response.

Decision tools and examples 117 Example 6 Challenging Conditions for Large Space Achieves STI 0.56 Description: Large concessions space Year commissioned: 1953/1998 TechnicAl DATA Daytime ambient noise level 68 dBA Leq Announcement SPL 69 dBA Leq Nighttime ambient noise level 64 dBA Leq STI range 0.61 (low ceiling area at counters) 0.51 (high ceiling area at tables) Uniformity ± 3 dBA Reverberation Time (RT60) 1.6 sec at 500 Hz 1.6 sec at 2,000 Hz ArchiTecTurAl/AcouSTicAl DeTAilS Ceiling height 14 feet at low ceiling above food counters; 25 feet at higher ceiling above customer dining area; 35 feet at highest ceiling above customer dining area Finishes Acoustical tile suspended ceiling; tile floor; gypsum wall (though minimal wall surface area because court is open on both ends). PA SySTem DeTAilS PA system type Digital Paging microphone type N/A Loudspeaker type Perimeter ceiling mounted and wall mounted Loudspeaker spacing 4–8 feet Ambient-noise-sensing microphones Yes SPeech inTelligibiliTy DiScuSSion Despite ambient conditions and low announcement level, above-average speech intelligibility achieved. Challenging conditions include • Long reverberation time. • High ambient noise. • Excessive low-frequency energy tends to mask intelligibility at higher speech frequencies. • PA system frequency response is not smooth, with a “bump” at 2,500 Hz that can distort the sound. WhAT cAn be imProveD • Room acoustics: Minor benefits to be gained from increasing the acoustical absorption to reduce the reverberation time at high ceiling areas. Incorporate acoustical absorption to reduce the RT60 to below 1.5 seconds. This will reduce some of the daytime ambient noise. (See Chapter 6 re architectural design.) • High ambient noise: Incorporate noise control to reduce background sound from the HVAC system. NC 45 or lower. (See Chapter 6 re architectural design.) • Loudspeakers and PA system design: Improve PA system EQ per testing and commissioning procedures discussed in Chapters 8 and 9.

(a) Concessions area. Photo credit: Wilson Ihrig (b) Measured PA system uniformity and frequency response.

Decision tools and examples 119 Example 7 Moderately Challenging Space With Room for Improvement, STI 0.46 Description: TSA Screening Area Year commissioned: 2009 TechnicAl DATA Daytime ambient noise level 58–60 dBA Leq Announcement SPL 63 dBA Leq Nighttime ambient noise level 51 dBA Leq STI range 0.46 Uniformity ± 2 dBA Reverberation Time (RT60) 1.3 sec at 500 Hz 1.2 sec at 2,000 Hz ArchiTecTurAl/AcouSTicAl DeTAilS Ceiling height 28 feet Finishes Carpeted floor; hard panel ceiling; gypsum walls with large glass doors on one end. PA SySTem DeTAilS PA system type Unverified Paging microphone type Handheld Loudspeaker type Ceiling mounted Loudspeaker spacing 17 feet Ambient sensing microphones No SPeech inTelligibiliTy DiScuSSion This space is typical for small airports and other securely separated areas. Many aspects can be modified to provide substantial improvement. Challenging conditions include • Acoustically hard surfaces (especially ceilings and large surfaces such as walls and glass doors) • Moderately long reverberation time • High ambient noise from HVAC • PA system frequency response is not smooth, with a “bump” at higher frequencies 2,000 Hz and 5,000 Hz that can distort the sound. WhAT cAn be imProveD • Room acoustics: Substantial benefits to be gained from increasing the acoustical absorption to reduce strong reflections from the walls. (See Chapter 6 re architectural design.) • High ambient noise: Incorporate noise control to reduce background sound from the HVAC system; NC 45 or lower. (See Chapter 6 re architectural design.) • Loudspeakers and PA system design: – Increase announcement signal level and improve PA system EQ per testing and commissioning procedures discussed in Chapters 8 and 9. – Ambient sensing microphones would help offset some of the ambient noise.

(a) Small TSA screening area. Photo credit: Wilson Ihrig (b) Measured PA system uniformity and frequency response.

Decision tools and examples 121 Example 8 Highly Challenging Space With Room for Improvement, STI 0.36 Description: Lower Level of Gate Area Year commissioned: 2000 TechnicAl DATA Daytime ambient noise level 64–69 dBA Leq Announcement SPL 74 dBA Leq Nighttime ambient noise level 58 dBA Leq STI range 0.29–0.39 Uniformity ± 1 dBA Reverberation Time (RT60) 2.9 sec at 500 Hz 3.5 sec at 2,000 Hz ArchiTecTurAl/AcouSTicAl DeTAilS Ceiling height 31 to 42.5 feet Finishes Terrazzo floor, gypsum board, partial coverage with perforated metal ceiling tiles. PA SySTem DeTAilS PA system type Digital Paging microphone type Handheld paging Loudspeaker type Wall-mounted speaker pairs at gates to supplement original high ceiling-mounted system Loudspeaker spacing 4 speakers, 2 at each gate Ambient-noise-sensing microphones Yes SPeech inTelligibiliTy DiScuSSion This is dual level space that can be found in many airports where the end group of gates features a full height ceiling with the gates on the lower level. Many aspects can be modified to provide substantial improvement. PA system frequency response is excellent without excessive low-frequency response. The uniformity of the PA sound coverage is also excellent in this area. Challenging conditions include • High ceiling • Acoustically hard surfaces (especially ceilings and large surfaces such as walls and glass doors) • Long reverberation time • Some ambient noise from HVAC and coupled areas at the mezzanine and upper levels WhAT cAn be imProveD • Room acoustics: Substantial benefits to be gained from increasing the acoustical absorption to reduce strong reflections from the walls. (See Chapter 6 re architectural design) • Loudspeakers and PA system design: Insufficient placement and number of speakers for these conditions; the uniformity is a measure of the reverberant sound field, but there is very little direct sound level

(a) Lower level gate area. Photo credit: Wilson Ihrig (b) Measured PA system uniformity and frequency response.

Decision tools and examples 123 Example 9 Satisfactory Ticketing Area, STI 0.61 Description: Ticketing near TSA Year commissioned: 2004/2008 TechnicAl DATA Daytime ambient noise level 63 dBA Leq Announcement SPL 67 dBA Leq Nighttime ambient noise level 51 dBA Leq STI range 0.55–0.64 Uniformity ± 2 dBA Reverberation Time (RT60) 0.9 sec at 500 Hz 1.0 sec at 2,000 Hz ArchiTecTurAl/AcouSTicAl DeTAilS Ceiling height 24 feet Finishes Terrazzo floor, suspended slat ceiling, glass exterior wall, gypsum board interior walls with acoustically reflective wood panels above ticketing counter and acoustical tile above ticketing agents. PA SySTem DeTAilS PA system type Digital Paging microphone type Handheld paging Loudspeaker type Left and right line arrays mounted above each main entry double door; each line array consists of four trapezoidal speakers Loudspeaker spacing 15 feet, on each side of double door Ambient sensing microphones Yes SPeech inTelligibiliTy DiScuSSion This ticketing space is providing desirable acoustics with a relatively low reverberation time, good coverage by line arrays, and clear announcements overall. Lower end of STI range measured 75 feet from entry doors in breezeway circulation space between Ticketing and TSA. PA system frequency response is good, but somewhat ragged in the mid-low ranges, which is detrimental to good intelligibility. Uniformity of PA sound coverage within this ADS is good. This space achieves most of the desired characteristics. WhAT cAn be imProveD • Loudspeakers and PA system design: Mid-low range could be improved

(a) Ticketing area. Photo credit: Wilson Ihrig (b) Measured PA system uniformity and frequency response.