Improving the Sound Quality of aircraft sounds by means of an Interactive Sound Synthesis Machine – Results of the COSMA Study

Reducing aircraft noise annoyance acoustically usually concentrates on lowering noise emissions for single aircraft components such as engines and high lift devices or optimizing noise abatement flight procedures. Although the overall sound pressure level of the aircraft contributes most to the acoustically related portion of annoyance, sound quality effects should not be disregarded in order to get clear technical guidelines to achieve less annoying aircraft sounds in the future. Within the EU-FP7-project COSMA (Community Oriented Solutions to Minimize aircraft noise Annoyance) an Interactive Sound Synthesis Machine was used by 156 subjects from 5 European laboratories to create own preferred sounds for 5 different aircraft (departure and approach each) by using faders assigned to attenuate or amplify several distinct acoustical parameters like buzz saw, tonal components, airframe noise etc. Basic technical constraints were considered, the overall loudness was kept constant at all times. The combined flight path and acoustical measurements of the aircraft were taken at Munich airport and its decomposed sounds were used as inputs for the faders. This method – as shown by the results – has distinct benefits compared to the Semantic Differential technique for judging single flyover events where it is particularly difficult for naïve subjects to assess the perceptual attributes even if they are trained