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93 C h a p t e r 9 9.1 Introduction This chapter presents the post-construction process (referred to as commissioning) for the PA system. Important steps in this process involve tuning, balancing, and other adjustments that can affect speech intelligibility. Many of the concepts discussed elsewhere in ACRP Research Report 175 are brought to bear during commissioning. For PA systems, it is important to have verification that the system is performing as designed and to optimize the system for its intended use within the framework of the built system; this process is known as commissioning. Commissioning is not intended to relieve the PA system vendor/installer of responsibility for providing a system that meets the projectâs specifications and other requirements. Commissioning offers an opportunity to fine-tune the system electronically within the constraints imposed by both the acoustics of the space and the electronic response of the PA equipment in the as-built condition. The vendor/installer should conduct testing (as discussed in Chapter 8), but an outside party also should review and test the installed system as part of a commissioning process. Key reasons to have the commissioning performed by an independent party include â¢ A separate task and budget will not be affected by potential cost overruns during installation. â¢ Although the vendor/installer and commissioning agent both have knowledge of the PA system electronics, a qualified and experienced commissioning agent also should have experience in acoustics and speech intelligibility in particular. â¢ A third party (other than the installer) can be part of an impartial quality assurance process to uncover and resolve problems such as those involving wiring or inadequate labeling and/ or documentation. The qualifications for the commissioning agent include familiarity with and experience in the following: â¢ Operation and design of PA systems in airports and similar large public interior spaces â¢ Optimization and testing of PA sound systems â¢ Room acoustics principles and acoustical measurements â¢ Speech intelligibility and STIPA measurement procedures Given that many of the key terms and concepts for commissioning are like those for Instal- lation in Section 8.3, only issues specific to commissioning PA systems at airports are discussed in the following sections. Commissioning Public Address Systems
94 Improving Intelligibility of airport terminal public address Systems 9.2 Overview Four steps have been identified in the overall process for PA system commissioning, as shown in Figure 9-1 (Cape and Smith 2005): 1. Prepare for commissioning. This includes basic verification of the system function, which may be included in the installation contract. 2. Generate a preliminary punch list, which forms the basis for substantial completion, and may be included in the installation contract. Items such as workmanship, installation delays, and equipment failure can be identified at this step. 3. Establish substantial completion. Once the items on the preliminary punch list have been completed, the system is ready for the commissioning agent to evaluate and optimize the system. 4. Inspect and test the system by the commissioning agent. 9.3 Key Concepts 9.3.1 Verification Verification occurs during the Basic Verification step and inspection and testing and confirms that the PA system meets the intent of design specifications contained in the contract documents (Cape and Smith 2005). The quantifiable elements include items that can be objectively verified (e.g., the number of electrical components, power ratings, and frequency response character- istics). Verification also encompasses review of the software, firmware, and hardware settings that affect the overall system performance such that the system provides the intended function of broadcasting live and recorded announcements over the PA system. Often the installer has performed a basic verification with appropriate tests to demonstrate and substantiate to their satisfaction that they have achieved the contractual obligations as part of the installation process (see Section 8.3). Specific verification tasks include â¢ Verifying and optimizing audio signal paths throughout the system â¢ Verifying that control systems and user interfaces are operating correctly and efficiently and providing the required functionality â¢ Completing all programming of audio devices and verifying their functionality â¢ Verifying that all contractual obligations have been met, including the complete system instal- lation and provision of documentation Figure 9-1. Steps in commissioning a PA system. Source: Adapted from Cape and Smith (2005)
Commissioning public address Systems 95 9.3.2 Optimization Optimization occurs during inspection and testing and is project specific, requiring the com- missioning agent to be familiar with the operation of PA systems in large public spaces and the evaluation of speech intelligibility, optimizing and sound system testing. Although PA systems at shopping centers and transportation stations have elements that are sometimes similar to airports (e.g., large volume/high ceiling rooms, elongated spaces, and high ambient noise levels), airports are unique in terms of security for airside and landside procedures. The diversity of public spaces within an airport and the nature of the secure environment and PA system announcements at airports are different from those of other large public spaces. The PA system technical staff, be they airport personnel or installer/operators, will have access to the secure login and control of the software for tuning and level adjustments, while the commissioning agent will advise PA system technical staff as to adjustments to be made during commissioning. These adjustments set the proper sound levels and equalization (frequency tuning the system), taking into account the acoustical conditions of each acoustically distinguishable space (ADS). 9.4 Inspection and Testing The three tests presented in the following subsections (9.4.1 through 9.4.3) were developed more fully in Chapter 8 because the basic preliminary work is expected to be completed by the installer. Commissioning and optimization adjustments are discussed below. 9.4.1 Balancing the System As was discussed in Chapter 7, there are three elements of the PA system, and each element can require adjustments for the system to function properly â¢ Input signal. It is good practice that the timbre and the levels for each input are as equal as possible in terms of natural sound and sound level. â¢ Amplifier (headend) gain settings. Proper gain structure should be optimized throughout the system to minimize noise and signal distortion. â¢ Zone gain and equalization settings. Given that each ADS can have different acoustical prop- erties and background conditions, adjustments at individual loudspeaker zones are necessary. Zones that are similar, with comparable acoustical and loudspeaker layouts, can have their settings copied and pasted to each area. However, all levels and STI measurements must be documented. 9.4.2 Setting PA Announcement Levels In addition to the information in Chapter 8, spatial averaging should be used for all equaliza- tion procedures. ASTM E336-16 includes a method for determining space-averaged levels by using fixed microphones or manually scanned microphonesâuse this method unless a more current method is developed specifically for use in STIPA measurements. A single microphone placement for analyzing and equalization is not recommended. The actual sound pressure level in a particular loudspeaker zone will depend on the background noise and acoustical conditions. After every adjustment of equalization, limiting, compressing, and/or microphone automatic gain control/level-setting, zone levels must be rechecked and adjusted. Each software module (e.g., local zone input, âall-callâ inputs, and recorded messages) should be checked for the gain structure appropriate to each zone. Level-setting is important for consistency of PA announce- ments and speech intelligibility throughout the airport.
96 Improving Intelligibility of airport terminal public address Systems 9.4.3 Loudspeaker Zone Equalization In addition to the steps listed in Chapter 8, consider that loudspeaker zone equalization settings are typically adjusted for good speech intelligibility. As discussed in Chapter 7, a natural-sounding system is desirable; this often requires some adjustment to the natural frequency response of the loudspeaker. High-end frequencies (e.g., 2,000 Hz and higher) should not sound harsh, and low- end frequencies (e.g., 125 Hz and lower) can be flat or turned down because the PA system is not being optimized for music quality. Furthermore, excessive low-frequency content through the PA system can reduce speech intelligibility. Overall, the goal is that reproduction should result in a natural sound. Zones that have very reverberant spaces, or where the ambient noise level is higher than other zones, may require further reduction of the low frequencies and limited amplification of the mid- and high-frequency bands (e.g., 500 Hz; 1,000 Hz; and 2,000 to 3,000 Hz). However, this can cause problems with the loudspeaker output recursively being picked up by the microphones (feedback) if the loudspeakers are close to the announcement microphone location. Loudspeakers installed above microphone locations may need to be set at a lower tap (level). Within the headend soft- ware, the âRing Mode Equalizingâ setting or feedback suppression should be activated, and the level and equalization settings should be rechecked and adjusted for all microphone inputs to that loudspeaker zone. Ring mode feedback equalization is possible on all DSPs using narrow-band parametric equalizers. In some cases, it may be necessary to induce feedback to test the ring mode control or to test if ring mode should be implemented. If the gain settings are somewhat unstable, cupping the microphone with the hands and moving the microphone around will produce feedback. Raising the gain slightly can also induce feedback for a borderline system. Use very high Q parametric filters (i.e., filters with narrow bandwidth) to reduce the feedback at each of the problem areas. However, if ring mode control is being used, it is not advisable to âover EQâ the system, because this can cause the broadcast signal to sound unnatural. Usually three narrow-band parametric equalizers are enough to fix the problems of gain before feedback. As with any adjustments, after these adjustments are made, the zone gain must be set back to the reference level. 9.4.4 Measuring and Reporting STI After the PA system has been initially balanced, equalized, and optimized, the speech intel- ligibility performance can be tested. If the STI performance does not meet the performance requirement, additional adjustments and optimization of the PA system may be necessary. The specific procedures for measuring STI are being developed by the industry to clarify procedures not defined in IEC 60268-16. ANSI is working with the industry trade group, InfoComm Inter- nationalÂ®, to establish a standard for measuring STI values. Various measurement methods and practices will be standardized, including microphone height and how to obtain a spatial average in each ADS. Following is an annotated list of the basic steps required; these steps typically are conducted during nighttime or after airline flight operations to avoid interference with airline operations and disturbance to passengers. 1. Measure the quiet ambient noise. This is the condition without the STIPA signal. This can be measured at a single location representing a passengerâs ear or spatially averaged between the typical passengerâs seated and standing positions. 2. Document announcement sound level. During nighttime hours, observe and document the nominal announcement sound level broadcast through the balanced and equalized system in each ADS. Typically, this is measured at several locations or obtained as a spatially averaged
Commissioning public address Systems 97 Leq. Document the level of each announcement source: standard recorded announcements and live announcements (e.g., gate announcements, fire department, paging, and text-to- speech). With this lower ambient noise condition, ambient-noise-sensing systems should have no effect on the PA signal. 3. Play the STIPA test signal. Broadcast the signal through the PA system via a a. waveform audio (WAV) file uploaded to the system server, b. direct input at the headend or at the gate microphone input, and/or c. live announcer simulator (talk-box) at the gate agent push-to-talk microphone. In all cases, the gain settings for the input signal should be adjusted so that the level of the STIPA signal matches the target signal level for the normal inputs fed through each of the above input sources (i.e., server, headend, or talk box). For example, if the signal level from recorded announcements is specified or designed for a nominal 75 dBA level at 5 feet above the floor, at any off-axis position from any loudspeaker, then the STIPA signal played through the PA system should generate a nominal 75 dBA level at the same locations. 4. Measure the STIPA signal. The test instrument automatically determines the measure- ment period. This is typically between 15 and 20 seconds, depending on the measurement instrument used. There can be no apparent extraneous noise during the measurement period (i.e., when the instrument is sampling the STIPA signal). For instance, if someone sneezes or slams a door during a measurement, the measurement should be discarded and a new one started. The measurement instrument will automatically determine if a sample is invalid. In this case, the instrument allows you to discard that test and repeat it. Good practice dictates that an average of at least three tests should be made at each measurement position. The instrument typically reports each individual test result as well as the average of all the samples at one position before the technician resets the meter for the next test position. a. Position the test microphone off-axis from any loudspeaker with the microphone at a nominal height 3 to 5 feet above the floor and no closer than 3 feet to any loudspeaker or flat surface. b. Conduct a stationary measurement at several locations within the ADS. An arithmetic average of all STI values measured in one ADS can be made if a single STI value is needed for that ADS. 5. Document results. Document these initial results in a memo and note whether or not the STI results are in conformance with contractual and code requirements. 6. Optimize and document. If necessary, make additional adjustments to the gain or equal- ization settings to compensate for the root causes of the nonconforming performance (e.g., background noise and room acoustics) and repeat the STI tests. It may be necessary to recommend physical changes to the installation, such as adding or upgrading loud- speakers. However, nonconforming areas, systems, and acoustical problems are usually documented during evaluation of existing systems. New systems should have been designed for proper coverage and acoustical conditions. Headend upgrades should have had tests during evaluation to document any requirements for additional loudspeakers and acous- tical treatments. Some design software allows the user to adjust loudspeaker types and locations for proper coverage and tap settings for SPL mapping within a space. Document these adjustments. Section 12.2.2 offers two examples that demonstrate how optimization and commissioning would improve the speech intelligibility of two different spaces. When the reverberation time is high, optimization would be helpful. Although use of high-performing acoustical ceiling tiles helps control reverberation time, there is still room for improvement.
98 Improving Intelligibility of airport terminal public address Systems 9.4.5 Troubleshooting the Speech Intelligibility of the PA System Installation The following can be considered if the STI result is lower than the target goal: Signal level: The nominal gain setting for the input may be need to be adjusted higher. Deter- mine whether the paging system microphone level or the prerecorded input levels need adjusting or additional equalization. Other issues with zone gain may bear investigating. Uniformity: â¢ If the loudspeaker spacing has not been optimized to achieve a consistent level (e.g., Â± 1 dBA) throughout the zone, the overall zone signal level may require increasing to achieve the target STI result. â¢ Poor uniformity and localized problems with dead zones or areas with less signal coverage may be due to individual loudspeakers or overall loudspeaker selection or layout. Ambient noise: â¢ High background noise levels (e.g., from mechanical equipment, passenger activities, televisions, or food court refrigeration units) may also require higher overall zone levels. â¢ This condition is typically outside the control of the PA system installer/commissioner; however, the localized condition at a particular ADS might be noisier than others. This fact is worth documenting and discussing with the AHJ to determine if it is possible to reduce the ambient noise. Ambient-noise-sensing system: Verify that this system is working properly. These are typi- cally set to provide up to about 5 dB gain for ambient noise levels higher (louder) than the quiet nighttime environment observed during installation and commissioning. Gain-sensing settings must be tested for feedback problems. In the software, raise the gain to the highest-level set in the noise-sensing module and test for feedback. Equalization: â¢ In adverse acoustical conditions, it may be necessary to attenuate the lower frequencies up to the 650 Hz band. Adding a low shelf filter to attenuate low frequencies with a 6 or 12 dB attenuation per octave slope can reduce the low-frequency content in the room and reduce the masking effect that such low frequencies and adverse reverberation can cause, both of which can reduce speech intelligibility. â¢ The higher frequencies (1,000 to 4,000 Hz) can have a strong effect on speech intelligibility, because the consonant sounds (/s/, /k/, /ch/, /t/, etc.) have strong components in this frequency range. Adjusting the EQ to boost the higher frequencies could be helpful. Reverberant conditions: â¢ These conditions are typically outside the control of the PA system installer/commissioner; however, the localized condition at a particular ADS might have more acoustically hard or challenging conditions than others. This fact is worth documenting and discussing with the AHJ to determine if it is possible to reduce the reverberant environment. â¢ Highly reverberant areas can benefit from a low shelf filter with a cut off frequency of 650 Hz to attenuate lower frequencies to help reduce the effects of low frequencies, reverberation, and masking. â¢ Wall locations and higher directivity loudspeakers can improve the situation. Sound should only be directed to the areas of occupied passengers or personal for communication.
Commissioning public address Systems 99 9.4.6 Considerations for Combination Emergency and Non-Emergency Systems Subject to local code requirements, the fire marshal can require tests of the emergency fire/mass evacuation cut-over system, which will require fire/emergency announcements and possibly STI measurements to evaluate adherence to Annex D of NFPA72 (NFPA 2016). If the PA system will be used for major mass evacuation, certain conditions may be required (e.g., UL-rated loudspeakers, end-of-line monitoring, and programming input logic to control priorities). The fire/emergency input to the PA system should be measured to document the STI. See Chapter 7 for additional information. 9.5 Final Checkout and Verification It is good practice to walk through the airport while it is in full operation. Listening to the dif- ferent zones at peak travel hours is important to obtain a subjective confirmation that everything is functioning properly. During this final step, there is often some minor adjustment required for some zones. This procedure will permit the commissioning agent to aurally verify the levels, proper operation, and intelligibility of all zones.