LABORATORY STUDY OF EFFECTS OF SONIC-BOOM SHAPING ON JUDGED LOUDNESS AND ACCEPTABILITY

A laboratory study was conducted to determine the effects of signature shaping of outdoor sonic booms on subjective loudness and acceptabili ty. The study utilized the sonic boom simula tor at the Langley Resear ch Center. A wide range of symmetrical, front-shock-minimized signatur e shapes was investigated together with a limited number of asymmetric al signatures. Subjective loudness judgments were obtained from 60 tes t subjects by using an eleven-point numerical scale. Acceptability jud gments were obtained using the method of constant stimuli. Results wer e used to assess the relative predictive ability of several noise desc riptors, determine the loudness benefits of detailed boom shaping, and derive laboratory sonic boom acceptability criteria. These results in dicated that the A-weighted sound exposure level, the Stevens Mark VII perceived level, and the Zwicker loudness level descriptors all perfo rmed well. Significant reductions in loudness were obtained by increas ing front-shock rise time and/or decreasing front-shock overpressure o f the front-shock-minimized signatures. In addition, the asymmetrical signatures were rated to be slightly quieter than the symmetrical fron t-shock-minimized signatures of equal A-weighted sound exposure levels . However, this result was based on a limited number of asymmetric sig natures. The comparison of laboratory acceptability results with accep tability data obtained in more realistic situations also indicated goo d agreement.