Frequency Spectrum of N Waves with Finite Rise Time

Several investigators have derived expressions for the pressure spectrum of the sonic‐boom N wave. Where the rise time is zero, Howes has shown that the pressure spectrum is a published spherical Bessel function. The present analysis shows that the spectrum with a finite rise time, not exceeding one‐tenth of the duration, can be closely approximated by multiplying two spherical Bessel functions, or, equivalently, by adding their logarithmic curves.