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Pages 70-88

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From page 70...
... 70 7.1 Introduction PA system design involves many factors, including not only the electronic components of that system, but also the space in which loudspeakers will be installed. This chapter provides (1)
From page 71...
... public address System Design 71 microphone input -- is the result of improper loudspeaker location and insufficient electronic gain control. Pick-up of unwanted outside signals can be caused by an aging system or poor installation.
From page 72...
... 72 Improving Intelligibility of airport terminal public address Systems prerecorded announcements will have adequate sound level and be free from noise and distortion. Loudspeaker selection is critical in PA system design because variation in output over a loudspeaker's frequency range introduces distortion, which diminishes intelligibility, particularly in the presence of noise.
From page 73...
... public address System Design 73 • Simpler training. Less microphone technique training is required, because there is no proximity effect in omnidirectional microphones.
From page 74...
... 74 Improving Intelligibility of airport terminal public address Systems 7.3.2 Other Paging Microphone Types Desktop (gooseneck) paging microphones, which are similar to handheld microphones in performance and function, are used where podium or desk stations are more convenient for paging or where vertical surfaces for the handheld microphone mounting plates are not available.
From page 75...
... public address System Design 75 7.4 Headend Electronics Headend electronics are components that constitute the "brains" of the PA system. Headend equipment constitutes the control center where most of the functional aspects of the PA system are established and stored.
From page 76...
... 76 Improving Intelligibility of airport terminal public address Systems pick-up) and transmits it to the DSP.
From page 77...
... public address System Design 77 Audio Power Amplifiers The role of the audio power amplifier is to amplify the low-power signals from the DSP to a level suitable for driving the loudspeakers. This step is where the signal levels are matched.
From page 78...
... 78 Improving Intelligibility of airport terminal public address Systems loudspeakers in high ceiling spaces are less desirable because they have to be operated at higher sound levels. This does not automatically result in better speech intelligibility.
From page 79...
... public address System Design 79 spaces. The columns are mounted at a low level so that the plane of sound coverage corresponds to the listener's ear height.
From page 80...
... 80 Improving Intelligibility of airport terminal public address Systems Steerable column arrays have less sound attenuation over a defined distance than standard box or passive column-array systems. This is a result of microprocessor control of the individual loudspeakers in the column and their interaction with each other.
From page 81...
... public address System Design 81 supports the higher sound levels required in noisy outdoor areas such as at curbside. Figure 7-9 shows examples of horn loudspeakers 7.5.5 Undesirable Loudspeaker Applications In a large space, wall-mounted nondirectional loudspeakers (e.g., cone loudspeakers in a box)
From page 82...
... 82 Improving Intelligibility of airport terminal public address Systems In a high-ceiling space, the challenges are different, because a loudspeaker that is too far from the listener will not have an adequate ratio of direct-to-indirect sound; the listener will not be able to understand announcements over the ambient noise. This is a case where a different type of loudspeaker must be considered.
From page 83...
... public address System Design 83 Where a distributed loudspeaker system can be used, the loudspeaker grid (i.e., loudspeaker spacing in the grid) depends on several characteristics, including • Ceiling height • Loudspeaker directivity • Loudspeaker sensitivity • Distance from any one loudspeaker to a listener • Acoustical conditions, including reverberation and noise From an intelligibility standpoint, the main goal of selecting a loudspeaker distribution pattern is to minimize the distance from a loudspeaker to a listener's ear, regardless of where a person stands.
From page 84...
... 84 Improving Intelligibility of airport terminal public address Systems Quality loudspeakers have an overall response of typically ± 5 dB over a broadband operating range between 70 Hz and 15,000 Hz with a smooth, linear response, typically ± 2 dB, in the speech frequency range between 200 Hz and 4,000 Hz. Coaxial construction, adequate magnet weight (10 oz.
From page 85...
... public address System Design 85 7.9 System Interfaces Level balancing is in the interface between live and prerecorded announcements. Specifically, no matter what the origin of the page, the sound level must be consistent and adequate at the listening location.
From page 86...
... 86 Improving Intelligibility of airport terminal public address Systems • PBX (phone system for paging) • Mobile phones (for messaging to phones or smart devices)
From page 87...
... public address System Design 87 can be used with a new or updated digital headend with very good results. Inspect all loudspeakers and address previous connection issues.
From page 88...
... 88 Improving Intelligibility of airport terminal public address Systems • Sourcing of materials. Although many of the materials for the enclosures and electronics can be widely sourced, all audio electronics require some small amount of rare metals, and some permanent magnets in loudspeakers may also use rare metals such as neodymium.

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