Effective Perceived Noise Level Evaluated for STOL and Other Aircraft Sounds.
WYLE LABS ROCKVILLE MD
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A paired comparison experiment was conducted in which a group of thirty two subjects evaluated, in a progressive wave field, the noisiness of sixty recorded aircraft flyover sounds. Thirty of these recordings were from short take-off and landing STOL AIRCRAFT. The complete set included a wide range of turbofan, turbojet, piston engine and turboprop powered aircraft in a variety of categories. The results were analyzed to test the ability of the Effective Perceived Noise Leval EPNL and other scales to predict the subjective responses. Because the sample of aircraft sounds was unusually large in number, variety, dyanmic range and duration, the test was considered to be severe. The main conclusion of the study is that the EPNL procedure performs as well for the STOL sounds as it does for the CTOL conventional take-off and landing aircraft sounds and may thus be used with equal confidence for rating the sounds of aircraft in both classes. When the sounds were divided into propulsion system categories it was found that EPNL, in common with other scales, performed most consistently for jets, piston engined aircraft and turboprops, in that order. In general, the integrated duration correction proved superior to an approximate correction based on the 10 dB-down duration. Analysis of the results showed that the average magnitude of the tone-correction was more than 3 dB and that corrections were automatically applied in practically all cases. In the case of propeller aircraft sound it is apparent that low frequency harmonics invoke tone corrections, whereas the subjective results suggest they are not required. Author