Factors Contributing to the Loudness of Sonic Booms

Abstract

Most of the flyover tests on subjective reaction to sonic booms have relied only on peak overpressure as a measurement standard. Loudness is, however, greatly influenced by wave shape, and by rise time in particular. Oncley and Dunn [J. Acoust. Soc. Am. (to be published)] have derived a simple expression for the energy spectral density of N waves with finite rise time. Loudness computations based on this expression agree well with the experimental results of Zepler and Harel, and also explain the extreme variation in loudness within a comparatively small range of overpressure. Actual sonic-boom analyses frequently show rise times of 10 msec or more, generally increasing with altitude. Since flyover tests have usually used fighter aircraft at 30 000 to 40 000 ft to simulate the pressure levels at twice that altitute from the SST, it is probable that on the average, booms were louder and sharper than the SST would produce. Conditions under which boom loudness can be reduced by configuration control will be considered.