To what extent the number of overflights can be increased without enhancing annoyance, if aeroplanes become softer? An original B737 take-off sound (sound-pressure level: Lmax=76dB(A)) was either reduced or amplified by 4.8dB. In a 3x3 factorial design, nine groups of ten subjects were exposed for 27 minutes to 3, 9 or 27 copies of either of these three sounds. Regarding energy equivalence defined by Leq(A)=const, a 4.8-dB sound-pressure reduction compensated for three times the number of the higher level, achieving constant Leq-levels in the diagonals of the design.
After noise exposure, cardiovascular responses, and the subjects ratings of loudness, annoyance, and quality of an imagined living area with comparable noise load were analyzed statistically. Comparison of the equal-energy conditions revealed no difference regarding heart rate and blood pressure, but subjective loudness increased with both level and number, and 27 soft aircraft were rated extremely loud. However, annoyance decreased, when 3 loud overflights were converted to 9 medium events, but increased again under 27 soft events. Imagined living-quality always decreased with increasing numbers of events, and could not be compensated for by energy preserving reduction of single-event levels.
Conclusion: Beyond 10 events per 30 minutes the number probably has an increasing over-energetic impact on subjective noise effects.
Referat in der Gruppe Verkehrspsychologie, Mittwoch, 31. März 1999, 11:00, HS 21
