Laboratory Study of Effects of Sonic Boom Shaping on Subjective Loudness and Acceptability

A laboratory study was conducted to determine the effects of sonic boom signature shaping on subjective loudness and acceptability. The study utilized the sonic boom simulator at the Langley Research Center. A wide range of symmetrical, front-shock-minimized signature shapes were investigated together with a limited number of asymmetrical signatures. Subjective loudness judgments were obtained from 60 test subjects by using an 11-point numerical category scale. Acceptability judgments were obtained using the method of constant stimuli. Results were used to assess the relative predictive ability of several noise metrics, 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 mctrics all performed well. Significant reductions in loudness were obtained by increasing front-shock rise time and/or decreasing front-shock over'pressure of the front-shock-minimized signatures. In addition, the asymmetrical signatures were rated to be slightly quieter than the symmetrical fTvnt-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 obtaiT_cd in more realistic situations also indicated good agreement.