Subjective Loudness of Sonic Boom: N-Wave and Minimized ('Low-Boom') Signatures.
Interim rept. 1 Jan-31 Dec 77,
TORONTO UNIV (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 booms. Test series I compared N-waves over a range of 0.22 to 10 ms rise time, 100 to 250 ms duration and 0.5 to 2.0 psf 24 to 96 Nsq m peak overpressure. In one sequence, tradeoff between rise time and overpressure was measured for equal loudness in another, the tradeoff between duration and overpressure. For equal loudness 10 ms rise time required 8 dB higher overpressure than for 1 ms rise time. Duration had little effect in the range 100 to 200 ms but at 250 ms noticeably enhanced the loudness. These results confirm those measured by Shepherd and Sutherland, made at 1 ms rise time and above except for the anomalous enhancement at 250 ms duration, and extend the measurements down to 0.22 ms. There is also good agreement with theoretical predictions Johnson-Robinson, Zepler-Harel methods except for the 10 ms rise time and 250 ms duration cases.