When the experimental XB-1 aircraft achieved supersonic speeds on a test flight, it did not create a disruptive sonic boom – thanks to a physics phenomenon called the Mach cutoff

Boom Supersonic’s XB-1 creates a sonic boom inaudible from the ground below when flying at the exact right speed and altitude.

The scaled-down prototype, nicknamed the "Baby Boom", broke the sound barrier for the first time during a test flight over the Mojave Desert in California in late January. The small jet, officially called XB-1, reached an altitude of 35,000 feet before accelerating to Mach 1.1 (844mph) – "10% faster than the speed of sound", said Sky News.