I get from pictures that the waves in front of the craft get closer and closer together until at Mach 1 they are on top of each other and boom! but! after that, the sound waves form a cone... what is that? is that the head of each wave being produced behind the previous wave and then blasting through it as the plane pushes through each sound wave? the cone gets pointier as the craft moves faster. Does the sound get louder as the the plane pushes sound waves through more previous ones, or are the sound waves just stretched farther apart only. I am imagining the Doppler effect would stretch the cone like it does the waves prior. But that is just a guess on my part.