Some Audio Considerations in Air Control Towers
Speech intelligibility tests were constructed by including within the framework of standard airplane-tower phraseologies standard multiple-choice word lists. In a laboratory room two mock control towers were constructed, one having six individual loudspeakers for each of six potential message sources, the other having but a single loudspeaker for the same six sources. In each mock tower the speaker array could be placed on the ceiling behind the operator's head, on the wall-ceiling angle in front of the operator, or at head height in front of the seated operator. Other experimental variables included signal level, noise level, and the density of messages per message source. Each tower was manned by a series of actual air-controllers operating in pairs. These pairs of operators listened to the same recorded materials at their respective towers and responded orally to all messages. The speed and accuracy of their responses were the test criteria. The results indicate that: six loudspeakers serve better than one for monitoring six nearly saturated message sources; the positioning of the loudspeaker array is not critical; ambient noise levels of 70 db cause no appreciable decrement in performance, but noise levels of 80 db and greater do.
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