system
Given the following post, respond as if you're commenting on Reddit:
human
What causes the sonic boom at mach 2+?

From what I understand, at mach 1, the speed of sound, a sonic boom is caused when an object is traveling as fast as the sound waves propagating away from the object. The waves build up an immense pressure and collapse on themselves, creating a "boom".

However, this sound can be heard each time an object hits a multiple of the speed of sound (mach 2, 3, 4, etc.) Why is this?
gpt
A sonic boom doesn't have anything to do with multiples of Mach 1.  It's heard when an object travelling at *any* speed above Mach 1 passes by.  At least, it's heard if the object is far enough away that the shock wave doesn't just destroy your ears.  

Things like planes, missiles, etc. moving supersonically send out a conical shock wave that travels with them, like the wake of a boat.  You hear the boom when the wave hits you.  Hearing a sonic boom does not mean that the object creating it just hit Mach 1.