I noticed in couple of videos of big explosions muffled sound right after the explosion flashes but before the shockwave. What is this sound?

Here are some examples from the net:

  • $\begingroup$ I think it would be at least interesting to look at how the sound for those videos originated: in particular how well it was synced with the video an whether it was dubbed, which it may have been for some of them. $\endgroup$ – tfb Sep 28 '16 at 14:30
  • $\begingroup$ I agree but I doubt that this is some video to sound synchronization effect. $\endgroup$ – Todd Sep 28 '16 at 15:03
  • $\begingroup$ In the first at least the initial thump is the detonation cord: you can see the flash in a couple of frames at the bottom of the picture. I have no trust in the sound of the second at all. Have not looked further, sorry. $\endgroup$ – tfb Sep 28 '16 at 16:45
  • $\begingroup$ I agree with @tfb, you should not hear anything due to the explosion before the shock wave (unless some small projectile ejected during the explosion propagated ahead of the main shock, which would produce its own "little" shock). The piston (i.e., heated and compressed air in explosions) travels faster than sound, thus sound waves should not out-run it. If you hear something before the shock, it came from something else... $\endgroup$ – honeste_vivere Sep 28 '16 at 19:23
  • $\begingroup$ Ok, I am removing the second link because it is unreliable indeed and putting the recent SpaceX explosion on its place, where is the detonation cord in this video? $\endgroup$ – Todd Sep 28 '16 at 22:19

A pressure wave can travel through solids at a greater speed than through air. And this means a "pre sound" can reach you before the shock wave does - as the motion of the ground will in turn induce a sound wave in the adjacent air.

  • $\begingroup$ Yes, this matches with the research and observations I made. I came to the conclusion that this sound is from the P-wave of the earthquake made by a big explosion which travels approximately 2 to 8 km/s in the Earth's crust and can be heard only in big enough explosions. $\endgroup$ – Todd Sep 29 '16 at 9:03
  • $\begingroup$ I thought this as well, but my initial assumption was that the amplitude would be too small for the speaker to respond but perhaps I was wrong. $\endgroup$ – honeste_vivere Sep 30 '16 at 12:53
  • $\begingroup$ The amplitude depends from the size of the explosion, that's why you can't hear it from a small explosion because the amplitude/energy propagated through the earth is too small. $\endgroup$ – Todd Oct 2 '16 at 10:21

Technically a shockwave is a propagating disturbance that travels faster than soundwaves in a particular medium. If the wave travels slower than sound it isn't a shockwave. The answer to your question though is that the energy and displacement of pressure that are the "shockwave" you're probably thinking of, propagate through air at a slow speed than sound waves do.

  • $\begingroup$ No, I know what a shockwave is, and it is clearly visible where it is and how it is propagating from most of the videos. This sound I hear is before the shockwave. $\endgroup$ – Todd Sep 28 '16 at 14:12

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