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Audibility and Annoyance of en Route Noise of Unducted Fan Engines
BBN SYSTEMS AND TECHNOLOGIES CORP CANOGA PARK CA
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Aircraft flyovers heard in high ambient noise urban environments are composed in large part of high absolute level, broadband noise. In contrast, noise exposure created en route by aircraft powered by unducted fan engines is expected to be relatively low in level, but to contain prominent low frequency tonal energy. These tones may be readily audible in low ambient noise rural environments. The annoyance of noise intrusions of low absolute level has been shown to be closely related to their audibility. Thus, one way to predict the annoyance of high altitude overflights by aircraft equipped with unducted fan engines is to estimate their audibility relative to that of conventionally powered aircraft in various ambient noise conditions. These predictions may be converted into estimates of the probability of high annoyance by means of a dosage-response relationship derived from laboratory data about the annoyance of individual noise intrusions. The latter estimates may in turn be applied to populations exposed to unducted fan engine noise over a range of assumed exposure levels. Application of these procedures to several assumed exposure cases suggests that millions of people in rural areas of the United States would be likely to be highly annoyed by the noise of aircraft powered by unducted fan engines. SDW
APPROVED FOR PUBLIC RELEASE