[1]: https://ascent.aero/project/acoustical-model-of-mach-cut-off...
[2]: https://etda.libraries.psu.edu/catalog/18490zfh5044
Including the obligatory scepticism from the peanut gallery that "Supersonic flight without an audible sonic boom" was even possible.
[1]: https://ascent.aero/project/acoustical-model-of-mach-cut-off...
[2]: https://etda.libraries.psu.edu/catalog/18490zfh5044