JFK Assassination Forum
JFK Assassination Plus General Discussion & Debate => JFK Assassination Plus General Discussion And Debate => Topic started by: Charles Collins on February 16, 2022, 03:33:17 PM
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There appears to be some active members here who are experienced in some of the technical matters concerning the assassination. This thread is a request for assistance in understanding potential reasons why the sound of the first shot was reported by so many witnesses in Dealey Plaza to be a different (fire cracker) sound than the other two shots. Here is a link to a summary of gunshot acoustics by Robert C. Maher, Montana State University:
https://www.montana.edu/rmaher/publications/maher_aac_0406.pdf (https://www.montana.edu/rmaher/publications/maher_aac_0406.pdf)
It is written in a manner which I think that most people can get a grasp on the basics of the physics of the sound of a high powered rifle. What remains a little mysterious to me however is how the shock wave propagates from the supersonic bullet. It is shown to be perpendicular to the angle of the shockwave cone. And when the microphone was placed behind the rifle, there was no sound of the shockwave at all, but the muzzle blast is still recorded. My questions are:
1. Does the shockwave sound behave differently than normal sound waves which are typically omnidirectional?
2. Does the perception of the shockwave sound depend upon being in a position in which its travel (perpendicular to the shockwave cone) would hit the person?
That is the way that it appears to be to me based on what is in the above referenced summary. Please let me know if you have the answers to my questions. Thanks.
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There appears to be some active members here who are experienced in some of the technical matters concerning the assassination. This thread is a request for assistance in understanding potential reasons why the sound of the first shot was reported by so many witnesses in Dealey Plaza to be a different (fire cracker) sound than the other two shots. Here is a link to a summary of gunshot acoustics by Robert C. Maher, Montana State University:
https://www.montana.edu/rmaher/publications/maher_aac_0406.pdf (https://www.montana.edu/rmaher/publications/maher_aac_0406.pdf)
It is written in a manner which I think that most people can get a grasp on the basics of the physics of the sound of a high powered rifle. What remains a little mysterious to me however is how the shock wave propagates from the supersonic bullet. It is shown to be perpendicular to the angle of the shockwave cone. And when the microphone was placed behind the rifle, there was no sound of the shockwave at all, but the muzzle blast is still recorded. My questions are:
1. Does the shockwave sound behave differently than normal sound waves which are typically omnidirectional?
2. Does the perception of the shockwave sound depend upon being in a position in which its travel (perpendicular to the shockwave cone) would hit the person?
That is the way that it appears to be to me based on what is in the above referenced summary. Please let me know if you have the answers to my questions. Thanks.
The first shot was taken by Oswald with the barrel of the rifle retracted inside the room. The second shot he had the rifle extended outside the window. A number of TSBD employees inside the building only recall one shot and also the dust on Bonnie Ray Williams from the concussion of the rifle blast would be explained by the rifle being fired with the barrel being completely inside the room.
The Secret Service and Police were looking at the windows of the buildings looking for a sniper. A protruding rifle barrel would have brought an immediate response.
There would be a definite sound difference between the two different positions of the rifle. The second shot would most likely have a different echo component to it with the barrel extended outside the window.
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The first shot was taken by Oswald with the barrel of the rifle retracted inside the room. The second shot he had the rifle extended outside the window. A number of TSBD employees inside the building only recall one shot and also the dust on Bonnie Ray Williams from the concussion of the rifle blast would be explained by the rifle being fired with the barrel being completely inside the room.
The Secret Service and Police were looking at the windows of the buildings looking for a sniper. A protruding rifle barrel would have brought an immediate response.
There would be a definite sound difference between the two different positions of the rifle. The second shot would most likely have a different echo component to it with the barrel extended outside the window.
The Secret Service and Police were looking at the windows of the buildings looking for a sniper. A protruding rifle barrel would have brought an immediate response.
I agree, however that is why I believe that the sniper waited until the limo was past his window. An ambush from behind is his best bet to be able to get a few shots off before being detected. I also believe that basic military training and a military mindset would help a potential sniper instinctively know this.
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The first shot was taken by Oswald with the barrel of the rifle retracted inside the room. The second shot he had the rifle extended outside the window. A number of TSBD employees inside the building only recall one shot and also the dust on Bonnie Ray Williams from the concussion of the rifle blast would be explained by the rifle being fired with the barrel being completely inside the room.
The Secret Service and Police were looking at the windows of the buildings looking for a sniper. A protruding rifle barrel would have brought an immediate response.
There would be a definite sound difference between the two different positions of the rifle. The second shot would most likely have a different echo component to it with the barrel extended outside the window.
This is, more or less, what Amos Euins witnessed.
At the first shot he states just a small part of the barrel was sticking out of the window:
Mr. Specter: And how long was the piece of pipe that you saw?
Mr. Euins: It was sticking out about that much.
Mr. Specter: About 14 or 15 inches?
After the first shot the shooter moves forward exposing more of the rifle:
Mr. Euins: Well, when he stuck it out, you know--after the President had come on down the street further, you know he kind of stuck it out more, you know.
Mr. Specter: How far was it sticking out of the window would you say then, Amos?
Mr. Euins: I would say it was about something like that.
Mr. Specter: Indicating about 3 feet?
Mr. Euins: You know--the trigger housing and stock and receiver group out the window.
Mr. Specter: I can't understand you, Amos.
Mr. Euins: It was enough to get the stock and receiving house and the trigger housing to stick out the window.
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This is, more or less, what Amos Euins witnessed.
At the first shot he states just a small part of the barrel was sticking out of the window:
Mr. Specter: And how long was the piece of pipe that you saw?
Mr. Euins: It was sticking out about that much.
Mr. Specter: About 14 or 15 inches?
After the first shot the shooter moves forward exposing more of the rifle:
Mr. Euins: Well, when he stuck it out, you know--after the President had come on down the street further, you know he kind of stuck it out more, you know.
Mr. Specter: How far was it sticking out of the window would you say then, Amos?
Mr. Euins: I would say it was about something like that.
Mr. Specter: Indicating about 3 feet?
Mr. Euins: You know--the trigger housing and stock and receiver group out the window.
Mr. Specter: I can't understand you, Amos.
Mr. Euins: It was enough to get the stock and receiving house and the trigger housing to stick out the window.
That’s interesting, thanks. The sound from a high powered rifle consists of the sonic wave created by the supersonic bullet and the muzzle blast that is created by the gases and other materials exiting the muzzle behind the bullet. I am mostly interested in how the sonic wave is propagated. Apparently it’s propagated differently than normal sound waves. I believe that even if just the muzzle end of the barrel is exposed outside the window opening, that the sound should be similar to a situation where more of the rifle is exposed.
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Okay, I have read a little bit more and considered this question quite a bit more. And I do believe that my initial thinking is correct. I believe that the sonic shock wave behaves differently from normal sound waves. A simplified analogy would be the wake of a boat traveling on the surface of a body of water. The most obvious difference being that the surface of the water is essentially a flat, one-dimensional plane. Whereas a supersonic bullet usually travels in a 3-dimensional air space. But I believe that the basic behavior (aka:its propagation) of a shockwave from a supersonic bullet is similar to the boat wake but the shockwave is 3-dimensional. Does this make sense? And does anyone disagree and have an alternative explanation?
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I’m catching up on this thread, another large honey-do project has me distracted.
I would agree with these comments that the sound of the first shot might sound somewhat different based on the gun position. As I recall, and maybe it was in Max Hollands National Geo video, that an early shot would require a steeper downward aim, and that would require putting the end of the barrel further back, perhaps in or near the plane of the window rather than sticking out much. I also seem to recall that Elsie Dorman mentioned the first sound being different and like some of it was actually coming from inside the building.
I’m not an expert in ballistics, but did look at shock waves a little bit during an earlier discussion with someone on another forum, so I’ll try to share what I know (or at least think I know) related to your questions. Others with expertise can probably correct or clarify any issues.
From what I understand, I think you basically have it right in what you have described, and that the shock was propagates out as sort of a straight line wave, but in three dimensions, along the sides of an expanding cone as it radiates out.
So the differences as I understand it is that in 3 dimensions the (point source) muzzle blast expands as a sphere, were as the components of the shock wave are constantly created along the path of the bullet, and the sound at the point of creation also radiates as a sphere, but due to the bullet movement the sounds created superimpose creating the surface of a cone which builds up the strong shock wave that radiates out at an angle from the bullet path determined by bullet speed (Mach value).
Comparatively, the way I understand it, is that the muzzle blast is from the hot gasses exiting the barrel which disrupts the air at a concentrated point area at the muzzle exit, the sound source. As you said, the sound propagates omnidirectional from there, basically as the surface of an expanding sphere. The sound Intensity (as power/unit area) decreases as 1/r^2 from the source since the surface area of the expanding sphere expands with r^2. Where r is the distance from source i.e. the sphere center.
The shock wave is created as the bullet constantly sheds off sound (a pressure wave) as the bullet travels and is seen as the angle of a cone relative to the bullet path, the angle depends on how fast beyond the speed of sound the bullet is going. The direction of shock wave propagation is perpendicular to the cone surface as it grows. The base of the expanding cone starts at the muzzle with the bullet moving forward and the wave goes mostly forward and out to the side from there, so behind the shooter there may be no shock wave encountered. I think the sound heard should be slightly different than a muzzle blast because of how the sound is created, and at its creation point along the path of the bullet the shock wave's net initial intensity may be lower than the initial intensity of the muzzle blast when one is closer to the gun (but intensity differences change with distance) and is probably at a higher frequency, hence the crack. The perceived direction of source for a muzzle blast would be directed towards the sounds source, the muzzle, and the shock wave would seem to radiate from a direction that is perpendicular to its source, the cone formed along the bullet path, which in not necessarily towards the gun. Being able to discern two separate sounds would depend on their arrival time to one's ear, which would probably need to be greater than 50-80 ms, so being able to hear two distinct sounds vs one compounded sound would also depend on direction and distance that one was positioned from the gun.
The boat wave is a good example of the shock type wave in two dimensions. Rotate that V-shape wake shape in 360 degrees around the boat path and you would have a “cone” shape. Maybe that’s what a fast submarine leaves behind?
I struggle with explaining stuff, so let me know if something seems unclear or not in agreement with the material you have seen.
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I’m catching up on this thread, another large honey-do project has me distracted.
I would agree with these comments that the sound of the first shot might sound somewhat different based on the gun position. As I recall, and maybe it was in Max Hollands National Geo video, that an early shot would require a steeper downward aim, and that would require putting the end of the barrel further back, perhaps in or near the plane of the window rather than sticking out much. I also seem to recall that Elsie Dorman mentioned the first sound being different and like some of it was actually coming from inside the building.
I’m not an expert in ballistics, but did look at shock waves a little bit during an earlier discussion with someone on another forum, so I’ll try to share what I know (or at least think I know) related to your questions. Others with expertise can probably correct or clarify any issues.
From what I understand, I think you basically have it right in what you have described, and that the shock was propagates out as sort of a straight line wave, but in three dimensions, along the sides of an expanding cone as it radiates out.
So the differences as I understand it is that in 3 dimensions the (point source) muzzle blast expands as a sphere, were as the components of the shock wave are constantly created along the path of the bullet, and the sound at the point of creation also radiates as a sphere, but due to the bullet movement the sounds created superimpose creating the surface of a cone which builds up the strong shock wave that radiates out at an angle from the bullet path determined by bullet speed (Mach value).
Comparatively, the way I understand it, is that the muzzle blast is from the hot gasses exiting the barrel which disrupts the air at a concentrated point area at the muzzle exit, the sound source. As you said, the sound propagates omnidirectional from there, basically as the surface of an expanding sphere. The sound Intensity (as power/unit area) decreases as 1/r^2 from the source since the surface area of the expanding sphere expands with r^2. Where r is the distance from source i.e. the sphere center.
The shock wave is created as the bullet constantly sheds off sound (a pressure wave) as the bullet travels and is seen as the angle of a cone relative to the bullet path, the angle depends on how fast beyond the speed of sound the bullet is going. The direction of shock wave propagation is perpendicular to the cone surface as it grows. The base of the expanding cone starts at the muzzle with the bullet moving forward and the wave goes mostly forward and out to the side from there, so behind the shooter there may be no shock wave encountered. I think the sound heard should be slightly different than a muzzle blast because of how the sound is created, and at its creation point along the path of the bullet the shock wave's net initial intensity may be lower than the initial intensity of the muzzle blast when one is closer to the gun (but intensity differences change with distance) and is probably at a higher frequency, hence the crack. The perceived direction of source for a muzzle blast would be directed towards the sounds source, the muzzle, and the shock wave would seem to radiate from a direction that is perpendicular to its source, the cone formed along the bullet path, which in not necessarily towards the gun. Being able to discern two separate sounds would depend on their arrival time to one's ear, which would probably need to be greater than 50-80 ms, so being able to hear two distinct sounds vs one compounded sound would also depend on direction and distance that one was positioned from the gun.
The boat wave is a good example of the shock type wave in two dimensions. Rotate that V-shape wake shape in 360 degrees around the boat path and you would have a “cone” shape. Maybe that’s what a fast submarine leaves behind?
I struggle with explaining stuff, so let me know if something seems unclear or not in agreement with the material you have seen.
Thanks Brian, your description does appear to me to be what I obtained from the Montana State University Summary and another source which was just some comments on another forum. If I understand the particulars of the speed of the Carcano bullet, it is approximately Mach 2. So using the formula in the MSU Summary, I came up with an angle of 30-degrees from the path of the bullet to the cone of the shockwave. Hopefully that is a reasonable approximation of the angle at the initial muzzle velocity anyway.
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Thanks Brian, your description does appear to me to be what I obtained from the Montana State University Summary and another source which was just some comments on another forum. If I understand the particulars of the speed of the Carcano bullet, it is approximately Mach 2. So using the formula in the MSU Summary, I came up with an angle of 30-degrees from the path of the bullet to the cone of the shockwave. Hopefully that is a reasonable approximation of the angle at the initial muzzle velocity anyway.
Yes, That sounds about right to me.
Your post peaked my interest on what I was saying in the past. I'll look and hopefully is was consistent with this :)
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Charles, I realized your thread here related to the shock waves you are exploring relates significantly to some z313 shot theories. I don’t want this discussion to get sidetracked, but your shock wave angle calculation of 30 deg directly raises a key issue.
There has been a major point being published by some researchers to help prove a z313 shot came from the Grassy Knoll.
Their supporting evidence is twofold.
A blur in Zapruders film at z313 could not have been caused by a startle reflex reaction, so it was:
1) A supersonic bullet going at least Mach 2 (M=2) and purportedly Mach 3 (M=3) or preferably Mach 4 (M=4), coming from a bullet shot from behind the fence on the grassy knoll and
2) The shock wave caused Zapruder’s camera to be displaced by virtue of it striking and shaking Zapruder and/or his camera right at z313.
Their argument sounds decent on the surface, but one that I think is just a gut-feel, grasping in air hypothesis that was never checked out.
I’m not sure if a bullet shock wave coming from Zapruder’s right would even be enough to nudge his camera (and probably not based on a video I saw below), but perhaps the easiest way to evaluate this scenario is to measure the angle formed from the hypothesized shooter’s position, to JFK, and to Zapruder at frame z313 and then compare that to the proposed frontal bullet Mach angle. If the angle formed by the (shooter/JFK/Zapruder) positions is greater than the Mach angle formed by the bullet at strike at z313, then the shock wave never reached Zapruder in time to cause the blur. If I call the shooters position point S (that is about 12 feet west from the north turn in the grassy knoll fence), and JFK’s position is K, and Zapruder’s position is Z, then the angle formed, / SKZ on the Google Earth map, is 36 deg
The Mach angle mu is calculated as mu=sin-1(1/M)
For M = 2 then mu=30 deg (as you calculated. It is marked in as a green line here on the diagram)
For M = 3 then mu=19.5 deg
For M = 4 then mu=14.5 deg
All these angles are all smaller than the observed personnel positioning angle of 36 deg, and the higher the Mach value the worse it gets. The shock wave never got to Zapruder in that time.
(https://drive.google.com/uc?id=1hJulJDPQBWEHOSR7-XdKaFZxONQ7q7ZB)
Secondly, here is an interesting video on how although a shock wave can sound loud when close to you and can obviously move your eardrum, it doesn’t do much else. In the video they had much more trouble with small gusts of wind on a house of cards than with a 50 BMG Mach 3 shock wave.
https://www.wideopenspaces.com/can-the-shockwave-from-a-50-bmg-really-kill-you/
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Mr. Euins: Well, when he stuck it out, you know--after the President had come on down the street further, you know he kind of stuck it out more, you know.
Mr. Specter: How far was it sticking out of the window would you say then, Amos?
Mr. Euins: I would say it was about something like that.
Mr. Specter: Indicating about 3 feet?
Mr. Euins: You know--the trigger housing and stock and receiver group out the window.
Mr. Specter: I can't understand you, Amos.
Who could?
That’s interesting ...
It sure is. Forget about muzzle blasts and sonic shock waves...That places a sniper hanging out that window by his knees.
What about the gun rest box--you know..the one with the scar on it? Someone probably put it back huh?
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Charles, I realized your thread here related to the shock waves you are exploring relates significantly to some z313 shot theories. I don’t want this discussion to get sidetracked, but your shock wave angle calculation of 30 deg directly raises a key issue.
There has been a major point being published by some researchers to help prove a z313 shot came from the Grassy Knoll.
Their supporting evidence is twofold.
A blur in Zapruders film at z313 could not have been caused by a startle reflex reaction, so it was:
1) A supersonic bullet going at least Mach 2 (M=2) and purportedly Mach 3 (M=3) or preferably Mach 4 (M=4), coming from a bullet shot from behind the fence on the grassy knoll and
2) The shock wave caused Zapruder’s camera to be displaced by virtue of it striking and shaking Zapruder and/or his camera right at z313.
Their argument sounds decent on the surface, but one that I think is just a gut-feel, grasping in air hypothesis that was never checked out.
I’m not sure if a bullet shock wave coming from Zapruder’s right would even be enough to nudge his camera (and probably not based on a video I saw below), but perhaps the easiest way to evaluate this scenario is to measure the angle formed from the hypothesized shooter’s position, to JFK, and to Zapruder at frame z313 and then compare that to the proposed frontal bullet Mach angle. If the angle formed by the (shooter/JFK/Zapruder) positions is greater than the Mach angle formed by the bullet at strike at z313, then the shock wave never reached Zapruder in time to cause the blur. If I call the shooters position point S (that is about 12 feet west from the north turn in the grassy knoll fence), and JFK’s position is K, and Zapruder’s position is Z, then the angle formed, / SKZ on the Google Earth map, is 36 deg
The Mach angle mu is calculated as mu=sin-1(1/M)
For M = 2 then mu=30 deg (as you calculated. It is marked in as a green line here on the diagram)
For M = 3 then mu=19.5 deg
For M = 4 then mu=14.5 deg
All these angles are all smaller than the observed personnel positioning angle of 36 deg, and the higher the Mach value the worse it gets. The shock wave never got to Zapruder in that time.
(https://drive.google.com/uc?id=1hJulJDPQBWEHOSR7-XdKaFZxONQ7q7ZB)
Secondly, here is an interesting video on how although a shock wave can sound loud when close to you and can obviously move your eardrum, it doesn’t do much else. In the video they had much more trouble with small gusts of wind on a house of cards than with a 50 BMG Mach 3 shock wave.
https://www.wideopenspaces.com/can-the-shockwave-from-a-50-bmg-really-kill-you/
Thanks Brian, the way I understand it is that the shockwave travels at the speed of sound in a direction 90-degrees to the angle of the cone. So say at Mach 2 the bullet is moving twice as fast as the shockwave. Therefore for the shockwave to reach Zapruder before the bullet reaches JFK, the distance from the shooter to JFK would have to be more than twice the distance from the shooter to Zapruder. It is clear from your diagram that this is not the case. And I agree that the faster bullet speeds would only make the difference even greater. The Montana State University study summary explains this and even shows graphs of the recordings which prove it to be true. And I agree the shockwave wouldn’t be powerful enough to physically move the camera. It might startle Zapruder into moving the camera but the reaction time for that to happen has to be considered also. Interesting video, thanks!
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I think I should add a couple of points to help explain this diagram some more.
First, this diagram is all based on a theoretical shot from the knoll striking JFK at z313. In this diagram I think the top end of that green line (which would be where the outside edge of the shock wave cone's base would be) would likely need to be extended upwards a little bit further than shown here. That would have that green line, as it moves in a direction perpendicular to itself, likely cross Zapruder's position but it would be after z313 so it could not be the cause of the Z313 shake. At higher mach values the green line would tilt further to the left, farther away from Zapruder and arrive to him even later. From the line diagrammed here onward in time, the green line shock wave would continue to move basically up the street parallel to Elm at that location at the speed of sound.
Also there would be a symmetric green line 30 deg below or South of the bullet path line segment SK representing the shock wave at ground level that is the from the other half or side of the total shock wave cone, moving generally downwards towards Main St.
I hope this helps a little more. Let me know if more clarification is needed.
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I think I should add a couple of points to help explain this diagram some more.
First, this diagram is all based on a theoretical shot from the knoll striking JFK at z313. In this diagram I think the top end of that green line (which would be where the outside edge of the shock wave cone's base would be) would likely need to be extended upwards a little bit further than shown here. That would have that green line, as it moves in a direction perpendicular to itself, likely cross Zapruder's position but it would be after z313 so it could not be the cause of the Z313 shake. At higher mach values the green line would tilt further to the left, farther away from Zapruder and arrive to him even later. From the line diagrammed here onward in time, the green line shock wave would continue to move basically up the street parallel to Elm at that location at the speed of sound.
Also there would be a symmetric green line 30 deg below or South of the bullet path line segment SK representing the shock wave at ground level that is the from the other half or side of the total shock wave cone, moving generally downwards towards Main St.
I hope this helps a little more. Let me know if more clarification is needed.
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.
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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.
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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.
(https://i.vgy.me/2GrxfC.gif)
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.
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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.
(https://i.vgy.me/2GrxfC.gif)
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
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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.
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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.
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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.
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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.
(https://i.vgy.me/dIZl97.jpg)
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.
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This diagram suggests the area (outlined in yellow) of the ground in Dealey Plaza that might be affected directly by a scenario of a second shot which hits JFK and JBC around the Z224 timeframe. Please take note of the vastly larger area affected as compared to either of the first shot scenarios diagramed and posted earlier in this thread. Of particular significance is the increased number of affected witnesses who's accounts we are familiar with.
(https://i.vgy.me/houBKa.jpg)
The calculated area affected directly by a shockwave from this shot is roughly 86,456 square feet. This is over 2.5 times as many square feet as the larger area of the two first shot scenarios posted earlier in this thread. And it contains vastly more witnesses who wouldn't have been directly affected by the shockwave of either of those two first shot scenarios but would be affected by this shot in this scenario. It seems reasonable to me that this could be a major reason the two shots reportedly sounded different to so many witnesses.
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This diagram depicts the area of the ground in Dealey Plaza that might be directly affected by the shockwave of a bullet which hits JFK in the head around the Z313 timeframe. It is significantly larger than the affected area of the second shot scenario posted earlier in this thread. And even more witnesses would be directly affected.
(https://i.vgy.me/jleccW.jpg)
The calculated affected area is roughly 108,788 square feet. This is well over 3-times the affected area of the largest of the two areas affected in the two first shot scenarios posted earlier in this thread. The same reasoning as stated in the second shot scenario applies to this scenario as to why I believe this to be a significant possible reason for the first shot to reportedly sound different than the last two shots.
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I found a cool photo by NASA of a shock wave by a supersonic bullet. Here’s a link to the webpage:
https://www.nasa.gov/mission_pages/galex/20070815/f.html (https://www.nasa.gov/mission_pages/galex/20070815/f.html)
Near the bottom of the NASA webpage there is a link to a high resolution photo of this.
Edit:
And a very cool video showing some shock waves and muzzle blasts:
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This diagram depicts the area of the ground in Dealey Plaza that might be directly affected by the shockwave of a bullet which hits JFK in the head around the Z313 timeframe. It is significantly larger than the affected area of the second shot scenario posted earlier in this thread. And even more witnesses would be directly affected.
(https://i.vgy.me/jleccW.jpg)
The calculated affected area is roughly 108,788 square feet. This is well over 3-times the affected area of the largest of the two areas affected in the two first shot scenarios posted earlier in this thread. The same reasoning as stated in the second shot scenario applies to this scenario as to why I believe this to be a significant possible reason for the first shot to reportedly sound different than the last two shots.
The first shot sounding different can be explained by the position of LHO's rifle. In your modeling you are not taking into account the fact the buildings along Houston Street and next to the TSBD act to reflect sound waves. Dealey Plaza was referred to as an echo chamber. Which is all explained in the HSCA Report.
For what it's worth. Attempting to understand the difference in perception of the shots, I shot a carcano from the living room of an unoccupied farmhouse while a friend stood outside to listen to the difference. Most notable was the large concussion from the shot, with the barrel retracted inside the room, and the fact it blew dust everywhere. Neither of which were experienced with the barrel extended outside the window, which makes perfect sense. Williams, Jarman, and Norman never referred to the first shot as sounding like a firecracker and Williams had dust on his hair. I have never taken the time to figure out where exactly that the phenomenon of a shot sounding like a firecracker started along the street. Garland Slack on Houston referred to the two shots followed by the sound of them striking JFK.
Garland Slack:
11/22
"I was standing there when the President's car passed and just after they rounded the corner from Houston onto Elm Street, I heard a report and I knew at once it was a high-powered rifle shot. I am a [cross-out] big game hunter and am familiar with the sound of hi [sic] powered rifles and I knew when I heard the retort [sic] that the shot had hit something. Within a [cross-out] few seconds I heard another retort [sic] and knew it also had hit something and all I could see was the highly colored hat that Mrs. Kennedy had on."
12/1:
"He said as the parade passed
the crowds pushed him and he was unable to see the car bearing the
President as it, proceeded west in front of the book store building .
However he said he had been a hunter and had been closely associated
with firearms for many years and he heard two shots in rapid
succession and realized from the sound that they most have been fired
from the interior of a building . He said he did not realize which
building because actually the sound as he first heard it seemed to
come from the direction of the overpass but its particular characteristics
made him feel it had to come from a building instead of from an
open area . "
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The first shot sounding different can be explained by the position of LHO's rifle. In your modeling you are not taking into account the fact the buildings along Houston Street and next to the TSBD act to reflect sound waves. Dealey Plaza was referred to as an echo chamber. Which is all explained in the HSCA Report.
For what it's worth. Attempting to understand the difference in perception of the shots, I shot a carcano from the living room of an unoccupied farmhouse while a friend stood outside to listen to the difference. Most notable was the large concussion from the shot, with the barrel retracted inside the room, and the fact it blew dust everywhere. Neither of which were experienced with the barrel extended outside the window, which makes perfect sense. Williams, Jarman, and Norman never referred to the first shot as sounding like a firecracker and Williams had dust on his hair. I have never taken the time to figure out where exactly that the phenomenon of a shot sounding like a firecracker started along the street. Garland Slack on Houston referred to the two shots followed by the sound of them striking JFK.
Garland Slack:
11/22
"I was standing there when the President's car passed and just after they rounded the corner from Houston onto Elm Street, I heard a report and I knew at once it was a high-powered rifle shot. I am a [cross-out] big game hunter and am familiar with the sound of hi [sic] powered rifles and I knew when I heard the retort [sic] that the shot had hit something. Within a [cross-out] few seconds I heard another retort [sic] and knew it also had hit something and all I could see was the highly colored hat that Mrs. Kennedy had on."
12/1:
"He said as the parade passed
the crowds pushed him and he was unable to see the car bearing the
President as it, proceeded west in front of the book store building .
However he said he had been a hunter and had been closely associated
with firearms for many years and he heard two shots in rapid
succession and realized from the sound that they most have been fired
from the interior of a building . He said he did not realize which
building because actually the sound as he first heard it seemed to
come from the direction of the overpass but its particular characteristics
made him feel it had to come from a building instead of from an
open area . "
Thanks, those are good points. I have considered them. And I stated that these diagrams are a simplified visual aid to try to explain just the shockwave aspect. I did say that I think that the shockwave propagation might have been a major factor. And I do realize that the shockwave doesn’t account for the entire differences or even is applicable to some of the witness accounts.
I would be interested in actually measuring some sound pressure levels and record the sound, preferably at various locations in Dealey Plaza with the rifle in various positions relative to the window. But something like your experience at the abandoned farmhouse would be interesting also. Did y’all make any measurements, or just have the subjective opinions? Do you still have access to the Carcano and ammunition for it? Did the HSCA acoustics investigation report anything like this? I remember reading something about the sound possibly being muffled to some unspecified extent if the rifle was inside the building. But nothing specific.
As far as the reflections of the shockwave goes, I intentionally stated that the outlined area is where the witnesses should be directly affected by the shockwave. Echoes are not part of the direct path of the shockwave from the path of the bullet to the witnesses. Just one of several reasons why they were not a part of this simplified explanation. But frankly, most of the reflective surfaces appear to me to be at angles that wouldn’t reflect the shockwave directly back towards most of the witnesses anyway. However, that doesn’t mean that I don’t believe that the echoes were a factor.