The 'boom' is relative to an observer. Just like a ship will produce a continuous wake but when you're standing on the shore of a canal the wake will pass you by.
Yup. The confusion, I think, comes from talk of sonic booms always being discussed along with mentioning an aircraft passing the sound barrier, going supersonic, whatever...
There is, I believe, a sudden change in aerodynamics when an aircraft passes the sound barrier - it IS a barrier of sorts. Aircraft had the power to pass this barrier, the problem was they would no longer fly correctly, or they would rip them selves apart, or some such thing once they hit mach 1.0.
People naturally got the idea that this phenomenon was related to the sonic boom itself.
