The propagation of Kaboom

[Brian Roselle]

Yes, that’s the way I understood it. I can easily get confused when adding or subtracting the angles involved and usually need to draw a diagram similar to yours in order to arrive at the correct conclusions. Of course these one dimensional diagrams are a simplification of what happens in the actual 3-D world, which includes the elevation changes (especially of the sixth floor window). But these diagrams can give us a rough idea of who was or wasn’t affected by a direct shockwave from the bullets.

Good point Charles. What I described is how I understand and what I would call the standard behavior of the shock wave. Something I forgot to consider here is the ground and changes in elevation that would have a role in what is encountered (like some reflection off the ground), and if there were other structures in its path, those blockages or reflections could also come into play etc. 
But hopefully the basic behavior should help anticipate what will generally transpire.

[Charles Collins]

The principal reason for me to begin this study is to explore a possible reason that many witnesses said the first shot sounded different than the other two shots. Some have suggested that the second two shots had the distinctive sharp crack of a high powered rifle but that the first shot sounded more like a firecracker or backfire. The shockwave created by the supersonic bullet is a big part of why the high powered rifles have the distinctive sharp crack sound. The shockwave is propagated much like a boat wake on the surface of a body of water (but in three dimensions). If a motor boat were to stop or slow down below "wake speed" a significant wake is no longer created. The same thing happens with a supersonic bullet (and it's shockwave) that stops or is slowed below the speed of sound.

I have taken Don Roberdeau's map and drawn some lines representing the various scenarios that I believe might have taken place in Dealey Plaza on 11/22/63. The first such image represents what I believe to be a rough idea of the propagation of the shockwave from a bullet that hits the mast of the traffic light in front of the TSBD.




The yellow outline represents the limits of the area on the ground that I believe would be affected directly by the shockwave of a bullet that hits the mast of the traffic light and is slowed below the speed of sound at that point. I calculate this area to be roughly 25,594 square feet.

The other scenario diagrams that I have prepared will follow as time permits.

[Jack Nessan]

The principal reason for me to begin this study is to explore a possible reason that many witnesses said the first shot sounded different than the other two shots. Some have suggested that the second two shots had the distinctive sharp crack of a high powered rifle but that the first shot sounded more like a firecracker or backfire. The shockwave created by the supersonic bullet is a big part of why the high powered rifles have the distinctive sharp crack sound. The shockwave is propagated much like a boat wake on the surface of a body of water (but in three dimensions). If a motor boat were to stop or slow down below "wake speed" a significant wake is no longer created. The same thing happens with a supersonic bullet (and it's shockwave) that stops or is slowed below the speed of sound.

I have taken Don Roberdeau's map and drawn some lines representing the various scenarios that I believe might have taken place in Dealey Plaza on 11/22/63. The first such image represents what I believe to be a rough idea of the propagation of the shockwave from a bullet that hits the mast of the traffic light in front of the TSBD.




The yellow outline represents the limits of the area on the ground that I believe would be affected directly by the shockwave of a bullet that hits the mast of the traffic light and is slowed below the speed of sound at that point. I calculate this area to be roughly 25,594 square feet.

The other scenario diagrams that I have prepared will follow as time permits.

The HSCA studied sounds and sound waves. Their study is under Analysis of Earwitness reports.

https://www.jfk-assassination.net/russ/jfkinfo/jfk8/sound2.htm

[Brian Roselle]

I think that diagram looks pretty good, those yellow lines look close to perpendicular to the cone surface and if the bullet and/or its fragment(s) all went subsonic at the tip of the red cone as drawn, then this diagram looks pretty representative of what I would expect to happen relative to a shock wave, and anyone to the right of the two angled yellow lines would likely not encounter any shock wave from such a shot.

I haven't checked out the reference link Jack just posted, it may provide some further insight.

[Charles Collins]

The HSCA studied sounds and sound waves. Their study is under Analysis of Earwitness reports.

https://www.jfk-assassination.net/russ/jfkinfo/jfk8/sound2.htm

Thanks Jack, I am interested in this because it contains some of their testing within Dealey Plaza. I am certainly not any kind of expert. But I am glad to see, at first glance, that my understanding of the basics of how the shockwave propagates agrees with what they describe. And it is interesting to see that their description of the loudness of the shockwave relative to the loudness of the muzzle blast indicates that they are both very loud. I will be interested to see how much the window opening might have muffled the muzzle blast if the rifle was completely inside the window. However, I don’t believe that the shockwave would have also been muffled because it is created by the supersonic bullet as it travels along its path. Therefore it seems to me that the first shot would have sounded very short (1-ms) and sharp (if the muzzle blast was muffled to any great extent). On the other hand, that shortness might be a possible reason that some witnesses apparently never recognized the first shot. This gets complicated very quickly. And these simplified diagrams I am creating are a very basic attempt to help visualize only one of the several aspects involved in the full picture.

[Charles Collins]

I think that diagram looks pretty good, those yellow lines look close to perpendicular to the cone surface and if the bullet and/or its fragment(s) all went subsonic at the tip of the red cone as drawn, then this diagram looks pretty representative of what I would expect to happen relative to a shock wave, and anyone to the right of the two angled yellow lines would likely not encounter any shock wave from such a shot.

I haven't checked out the reference link Jack just posted, it may provide some further insight.

Thanks for the input. I’m glad to know someone thinks along the same lines as I do. Yeah, the link Jack provided looks at first glance to be a worthwhile read.

[Charles Collins]

Here is another diagram showing a missed first shot hitting the pavement near the JFK limo around the Z133 area. If this scenario were to be correct, I believe that the bullet could conceivably ricochet off the pavement and continue on below the speed of sound to the areas of the mark around the sewer manhole cover and/or the curb near Tague's position.




I calculated the area depicted by the yellow outlines to be roughly 33,975 square feet of the ground which would be directly affected by the shockwave. A significant but not huge difference from the 25,594 square feet depicted in the scenario of the bullet hitting the mast of the traffic light.