In order to decrease disturbing noise to the local community produced by overflying aircraft, the ‘Sound engineering for aircraft’ (SEFA) project used complex sound engineering in an effort to define optimal or target aircraft community noise ‘shapes’ or sound characteristics. First, the researchers recorded sample sounds produced by 238 aircraft during take-off and arrival at three airports in Europe. They next used spectral decomposition and non-linear filtering to modify the recordings and create a huge database of several hundred synthesised sounds indistinguishable from those produced by real aircraft. The research team then carried out extensive psychometric tests involving subjective assessment of these overflying aircraft noise events by numerous individuals in eight laboratories in seven countries. Detailed statistical analysis of the data revealed a number of interesting findings. First, culture, age, gender, individual noise sensitivity and being a resident of an airport community had no effect on judgments of aircraft sounds. Overall, scaling of aircraft sounds was a very difficult task for the listeners given the rapidity with which the sound changes during take-off and landing. In addition, the significance given to any particular disturbing feature of the sound generated was largely dependent on the entire sound composition. Thus, characterising the optimal sound shape proved to be a much more complex task than originally anticipated. In order to eliminate the need for further costly and time-consuming tests such as those described previously, researchers on the SEFA project designed two extremely innovative simulation tools. The virtual aircraft tool provides a direct link between specific aircraft configuration sound and optimal target sound characteristics. The virtual listener tool simulates subjective evaluation of overflying aircraft sound based on scaling defined from the extensive psychometric tests. In summary, the SEFA project derived guidelines regarding aircraft frame design, engine design and flight procedures for noise reduction according to aircraft-specific features. The project thus elucidated methods to reduce disturbing noise beyond simply lowering noise levels, namely taking into account the characteristics of the specific noise signatures of given aircraft. The simulation tools created by the project team promise to bring better designs to the forefront very soon.
Sound Engineering For Aircraft (SEFA)
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29 December 2017