I happen to stumble upon this intriguing animation of a Tachyon, and immediately started to think about the same phenomenon, but with sound waves. I imagined a bandwagon B moving at a constant supersonic speed, and passing an stationary observer O.

                                                      <--- weeeeee
                         .                              .
                         O                              B

My understanding is, until B passes O, O would here nothing. Then, O would hear two bandwagons receding from her, after the sonic boom. One receding to the left, where the bandwagon has gone, and obviously redshifted. And one to the right, blueshifted. The sound to the right will also be heard as a receding bandwagon, because farther the bandwagon was, later the sound waves would arrive at O.

Is my understanding of this phenomenon correct? And do we have any real world examples of this?

  • $\begingroup$ Typically the double bang from a plane moving at supersonic speed comes from the front, and rear, shock waves $\endgroup$
    – user56903
    Nov 3 '14 at 10:07
  • $\begingroup$ @DirkBruere: It's not about the double bang. My question is about the sound heard after the sonic boom. $\endgroup$ Nov 3 '14 at 10:26

It would appear to be correct. An example is a supersonic bullet fired over your head from a few hundred metres distance. You hear the crack of the bullet's shock wave as it passes, the sound of the round fired and (if your hearing is till up to it) the kind of sucking sound the bullet makes as it travels downrange. I imagine that a better setup would be to get your computer to record the sound and examine the waveform in detail. If you are in the USA with its gun laws this should be easy to do.


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