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 acceptability. The study utilized the sonic boom simula tor at the Langley Research Center. A wide range of symmetrical, front-shock-minimized signature shapes was investigated together with a limited number of asymmetrical signatures. Subjective loudness judgments were obtained from 60 test subjects by using an eleven-point numerical scale. Acceptability judgments were obtained using the method of constant stimuli. Results were used to assess the relative predictive ability of several noise descriptors, determine the loudness benefits of detailed boom shaping, and derive laboratory sonic boom acceptability criteria. These results indicated that the A-weighted sound exposure level, the Stevens Mark VII perceived level, and the Zwicker loudness level descriptors all performed well. Significant reductions in loudness were obtained by increasing front-shock rise time and/or decreasing front-shock overpressure of the front-shock-minimized signatures. In addition, the asymmetrical signatures were rated to be slightly quieter than the symmetrical front-shock-minimized signatures of equal A-weighted sound exposure levels. However, this result was based on a limited number of asymmetric signatures. The comparison of laboratory acceptability results with acceptability data obtained in more realistic situations also indicated good agreement.