On the Loudness of Sonic Booms and Other Impulsive Sounds.
TORONTO UNIV DOWNSVIEW (ONTARIO) INST FOR AEROSPACE STUDIES
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A loudspeaker-driven simulation booth with extended rise time capability down to 0.22 ms has been used for subjective loudness tests of sonic-boom and other types of impulsive sounds. The first series compared N-waves over a range of 0.22 to 10 ms rise time, 100 to 250 ms duration and from 0.5 to 4 psf the latter for the longer rise times 24 to 192 Nsq m peak overpressure. The response tradeoff between rise time and overpressure, and duration and overpressure was measured. The second series tested certain flat top sonic boom signatures, which according to current theory could be generated by special very long SST aircraft designed for minimized sonic-boom these were compared for loudness with a reference N-wave pN 0.5 psf, 1 ms rise time, 150 ms duration. The third series compared filtered N-wave signatures, using a highpass digital filter with an unfiltered N-wave signature 1 psf, 1 ms rise time, 150 ms duration. In the last test series the tradeoff between overpressure and duration was found for idealized quarry blast signatures composed of sequences of 25 ms long pulses with 0.22 ms rise time. The range of durations extended from 25 to 400 ms. The results in each series were compared with theoretical predictions by the method of Johnson and Robinson. All but the long-duration quarry blast judgements were found to be in very good agreement in terms of relative loudness levels.