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FBI Decibel Test of C2766


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Bob,

I believe the 130 db and the statement that no one had ANY difficulty determining the origin of the test-shots came from Don Thomas' book which I mentioned in an earlier post on the "Paraffin" thread. I no longer have the book so I can't verify this.

The 120 db threshold of pain that you cited came from a study I was part of, which was used to require ear protection be provided for the ramp workers at major airports serving large jets. It did NOT endear us to management, but interestingly enough we received letters of commendation from the USAF and Air National Guard. The accepted criteria at the time was the range of 120-140db was the danger zone with hearing protection required above 140 and "suggested" above 120. As you stated, 140 db is one hell of a lot louder that 120.

Tom

Edited by Tom Neal
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The reason I am trying to find precisely where the decibel level of C2766 (130 decibels) was taken is that not everyone seems to think rifles are in the 130 dB range.

For comparison dB levels for some audible sounds are given below.

0-10dB Threshold of human hearing.

10-20dB Normal breathing, rustling leaves.

20-30dB Whispering at about 1.5 metres.

40-50dB Coffee maker, library, quiet office, quiet residential area.

50-60dB Dishwasher, electric shaver, office, rainfall, refrigerator, sewing machine.

60-70dB Air conditioner, alarm clock, background music, normal conversation, television.

70-80dB Coffee grinder, toilet flush, freeway traffic, hair dryer, vacuum cleaner.

80-90dB Blender, doorbell, heavy traffic, hand saw, lawn mower, ringing telephone, whistling kettle.

85dB Lower limit recommended for the wearing of hearing protection.

90-100dB Electric drill, shouted conversation, tractor, truck.

100-110dB Baby crying, boom box, factory machinery, motorcycle, subway train.

110-120dB Ambulance siren, car horn, leaf blower, walkman on high, power saw, shouting in the ear.

120-130dB Auto stereo, rock concert, chain saw, pneumatic drills, stock car races, thunder, power drill.

130-140dB Threshold of pain, air raid siren, jet airplane taking off, jackhammer.

150-160dB Artillery fire at 500 feet, balloon pop, cap gun.

160-170dB Fireworks, handgun, rifle.

170 -180dB Shotgun.

180 - 190dB Rocket launch, volcanic eruption.

http://www.eastcoastrip.org/did-you-know/infrasound

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Decibel (Loudness) Comparison Chart

Here are some interesting numbers, collected from a variety of sources, that help one to understand the volume levels of various sources and how they can affect our hearing.

Environmental Noise

Weakest sound heard 0dB Whisper Quiet Library at 6' 30dB Normal conversation at 3' 60-65dB Telephone dial tone 80dB City Traffic (inside car) 85dB Train whistle at 500', Truck Traffic 90dB Jackhammer at 50' 95dB Subway train at 200' 95dB Level at which sustained exposure may result in hearing loss 90 - 95dB Hand Drill 98dB Power mower at 3' 107dB Snowmobile, Motorcycle 100dB Power saw at 3' 110dB Sandblasting, Loud Rock Concert 115dB Pain begins 125dB Pneumatic riveter at 4' 125dB Even short term exposure can cause permanent damage - Loudest recommended exposure WITHhearing protection 140dB Jet engine at 100' 140dB 12 Gauge Shotgun Blast 165dB Death of hearing tissue 180dB Loudest sound possible 194dB
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Perceptions of Increases in Decibel Level

Imperceptible Change

1dB

Barely Perceptible Change

3dB

Clearly Noticeable Change

5dB

About Twice as Loud

10dB

About Four Times as Loud

20dB

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"4 .3 Loudness and Apparent Size of Acoustic Image

All observers rated the rifle shots as very very loud, and they were unable to understand how they could have been described as a firecracker or backfire . Only the pistol, which was subsonic, produced a moderate loudness ."

"Analysis of Earwitness Reports Relating to the Assassination of President John F. Kennedy by D.M. Green 1979"

http://www.history-matters.com/archive/jfk/hsca/reportvols/vol8/pdf/HSCA_Vol8_AS_3_Earwitness.pdf

This report was presented to the HSCA.

The authors of this reported also stated that, at one meter from the test rifle (C2766), the muzzle blast was measured at 157 decibels and that, at 30 feet from the muzzle, the sound was measured at 137 decibels. Nowhere does this report state whether these measured distances were going back or forward from the muzzle, or whether the measurements were taken 90° out from the side of the rifle.

Edited by Robert Prudhomme
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By now it should be obvious to everyone here that there is something drastically wrong with the Altgens 6 photo, seen below:

Altgens_Photo_Taken_During_Shooting.jpg?

This photo corresponds in time to the moment frame z255 of the Zapruder film was exposed. According to the WCR, two shots from a 6.5mm Carcano M91/38 short rifle have just been fired from a position slightly behind these spectators seen here and 62 feet above them; 3.5 seconds and 5.2 seconds before this photo was taken.

At the very MINIMUM, the loudness of these shots would have been 130 decibels. However, if the sound level one meter from the muzzle of the Carcano was 157 decibels, as reported to the HSCA, there is a strong possibility these spectators heard gunshots in excess of 130 decibels.

If the threshold of pain is at 120 decibels, why is there no reaction whatsoever seen on the faces of the spectators?

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Now Bob... you know I've been writing about this for years now. The following is one of the biggest load of crap offered. Not 12 feet from the supposed open-end of the barrel of this rifle at 120-150dB's and this man can claim to not only hear the bolt work and the shell hit the ground, but does so after 2 more of the same level sounds?

"I believe it came from above us" - Really people? and instead of screaming out the window - "He's up here" the run to the west windows to look at the RR Yard... hmmm.

I'm 100% with you Bob. The gunshot sounds on the motorcycle tape would have been LOUD - above anything else in DP that day.

As Castro said, a sniper would be farther away, hidden from sight and shooting from another building or location...

Mr. NORMAN. I believe it was his right arm, and I can't remember what the exact time was but I know I heard a shot, and then after I heard the shot, well, it seems as though the President, you know, slumped or something, and then another shot and I believe Jarman or someone told me, he said, "I believe someone is shooting at the President," and I think I made a statement "It is someone shooting at the President, and I believe it came from up above us."
Well, I couldn't see at all during the time but I know I heard a third shot fired, and I could also hear something sounded like the shell hulls hitting the floor and the ejecting of the rifle, it sounded as though it was to me.
Mr. BALL. How many shots did you hear?
Mr. NORMAN. Three.
Mr. BALL. Do you remember whether or not you said anything to the men then as to whether or not you heard anything from above you?
Mr. NORMAN. Only I think I remember saying that I thought I could hear the shell hulls and the ejection of the rifle. I didn't tell I think I hear anybody moving, you know.
Mr. BALL. But you thought, do you remember you told the men then that you thought you heard the ejection of the rifle?
Mr. NORMAN. Yes, sir.
Mr. BALL. And shells on the floor?
Mr. NORMAN. Yes, sir.

Recently I was looking at the initial reactions to the shooting and where DPD officers and DSO sheriff's went first (not to mention the ATF agents who also stormed the TSBD)

We all know Curry and Decker both specifically say to send people to the overpass, the RR yard yet where does Officer Baker run and why?

SENATOR COOPER - I didn't hear what he said he heard on the radio?
Mr. BAKER - I heard Chief Curry, the chief of the police over there, say, "Get some men over on the railroad track." I think everyone at that time thought these shots came from the railroad track.
Mr. BELIN - By "everyone" do you include you, too?
Mr. BAKER - No, Sir. I had it--I was in a better position due to the wind and you know under it, that I knew it was directly ahead, and up, and it either had to be this building here or this one over here.
Mr. BELIN - You are pointing to either the first building, you are pointing to the School Book Depository Building, and the second one you are pointing to is the one across the street. When you heard this announcement on your radio was it while you were parking your motorcycle?
Mr. BAKER - Yes, sir.

1 (Chief of Police Jesse E. Curry) Get a man on top of that triple underpass and see what happened up there. 1 (Chief of Police Jesse E. Curry) Have Parkland stand by. Dallas 1 (Sheriff J.E. "Bill" Decker) I am sure it's going to take some time to get your man in there. Pull every one of my men in there. Dispatcher Dallas 1, repeat, I didn't get all of it. I didn't quite understand all of it. Dallas 1 (Sheriff J.E. "Bill" Decker) Have my office move all available men out of my office into the railroad yard to try to determine what happened in there and hold everything secure until Homicide and other investigators should get there. 12:34 142 (Patrolman C.A. Haygood) I just talked to a guy up here who was standing close to it and the best he could tell it came from the Texas School Book Depository Building here with that Hertz Renting sign on top. 12:36 260 (Sergeant D.V. Harkness) I have a witness that says that it came from the 5th floor of the Texas Book Depository Store.

Harness and Haygood... men with Sawyer and enablers of the TSBD story..

Your work Bob has always been of help... keep on Truckin'

DJ

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Here is one for you, Dave. Did you know there is a way to make a shot originating from behind the limo appear, to ear witnesses, to have originated from down near the Grassy Knoll?

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While the alleged sniper weapon was unsurprised are we to assume that other weapons that may have been used that day were also unsurprised?

If one intended not to draw attention to oneself in order to increase the chances of getting away, would it not make sense to surpress things a bit?

Is his not consistent with reports that the shots sounded like firecrackers or backfires?

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Here is one for you, Dave. Did you know there is a way to make a shot originating from behind the limo appear, to ear witnesses, to have originated from down near the Grassy Knoll?

Other than natural echoes? Pray, do tell.

As I understand it, that silent carbine from WWII doesn't make a sound and is accurate and deadly from quite a distance...

Wasn't you who brought up diversionary sounds like an actual firecracker?

DJ

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Hi Steve

I don't believe I've seen you on this forum before. Welcome.

I believe shots came from at least two different sources; behind and in front of the limo. I also believe the plotters of the assassination did not intend to have this seen as the work of a lone nut, and fully intended to blame the assassination on a group such as the Cubans. The very fact they chose to assassinate JFK in broad daylight in front of a large crowd speaks volumes about this.

I think the most important thing on their minds was allowing the shooter(s) behind the limo the opportunity to make their egress, whether it was from the TSBD, the Dal-Tex Building or the County Records Building. The shooter in front of the limo, whether he was on the north or south knoll, or the underpass, was already on the ground, and didn't need nearly as much time to escape. Besides, there is a very good chance the shooter in front of the limo was merely a backup and was only supposed to shoot if the other shooter(s) were unable to eliminate JFK.

How this was accomplished is a bit complicated, and I will explain my theory in response to the post David Josephs made.

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Here is one for you, Dave. Did you know there is a way to make a shot originating from behind the limo appear, to ear witnesses, to have originated from down near the Grassy Knoll?

Other than natural echoes? Pray, do tell.

As I understand it, that silent carbine from WWII doesn't make a sound and is accurate and deadly from quite a distance...

Wasn't you who brought up diversionary sounds like an actual firecracker?

DJ

Hi Dave

The deLisle carbine was indeed completely silent, although whether or not it was as accurate as a high powered rifle is something I doubt. It achieved this silence simply because it was chambered for the .45 calibre pistol round. As this round is subsonic (under the speed of sound), there is no sonic boom heard as this bullet breaks the sound barrier. As the deLisle was also fitted with a suppressor, there was also no muzzle blast, and therefore this weapon was as silent as a bow and arrow. However, I must emphasize the great trade off in accuracy that is made going from a weapon shooting a supersonic rifle round to a weapon shooting a subsonic pistol round.

No, I never suggested a diversionary firecracker. In fact, I don't believe there was a need for such a thing. I believe there was one and possibly two shots that originated from behind the limo, fired from high powered rifle(s) fitted with suppressors. A shot from such a rifle would produce no muzzle blast but, as its bullet would be travelling at supersonic speeds (greater than the speed of sound), it would be breaking the sound barrier, and there would be a loud "crack" heard as it went by.

There is a popular myth that when an object breaks the sound barrier, it produces a sonic boom only at the instant it goes over the speed of sound and then, as it continues at supersonic speeds, it is silent. Nothing could be further from the truth. What actually happens is that object will make one continuous sonic boom for the entire distance and time it is travelling at supersonic speeds.

-------------------------------------------------------------------------------------------------------------------------

The Supersonic Crack

Any projectile moving through the air at a velocity greater than the speed of sound (332 to 340 m/s or 1,089 to 1,114 fps in dry, 18 C or 65 degree F air, depending on who one listens to) will create a supersonic crack. Temperature, humidity and atmospheric pressure variations play a role in raising or lowering the speed of sound by a small percentage. In a firearm which lacks a substantial muzzle report (being fired over an open field) the sound resembles the loud tearing of a bed sheet.

Two sounds are actually created, one from the front of the bullet, and one from the rear. Near trees and buildings the sound waves come back as a distinct crack or pop each time the speeding bullet passes some object with a vertical, reflective surface. Once the muzzle report has been diminished the supersonic boom becomes dominant. Curiously, the sounds will now appear to come from the target area, rather than the rifleman's position. Sound moves through our atmosphere at a relatively fixed rate. A sound wave will typically strike one ear a bit before the other.

The human brain is capable of detecting the difference in time between sound impacting one ear and then the other in an increment of as little as one/six-millionth of a second. With time and practice we soon learn to use this ability to pinpoint the source of a sound very accurately. Because a suppressed muzzle report is relatively quiet, the uninitiated will automatically home in on the loudest sound, which in this case is a sonic boom reflecting from the target area. The intense, sharp sound of the bullet's passage will seem much louder than the muzzle report to someone close to the flight path. Indeed, a rapidly moving .308 bullet will sound louder than a .22 LR pistol, to someone who is positioned a few feet from its flight path.

Smaller diameter bullets make less noise than larger diameter bullets. Supersonic is supersonic. A bullet traveling 366 m/s or 1,200 fps will make about the same noise as one traveling 1220 m/s or 4,000 fps. Projectiles that are .308 inch in diameter will be somewhat louder than .223 bullets. There is no technology which can remove the sound of a supersonic projectile, no matter what claims are made to the contrary.

http://www.silencerresearch.com/sound_suppressors_on_high_powered_rifles.htm

What this author is saying is a bullet will make a sonic boom all the way to its target (or until it slows to subsonic speeds many hundreds of yards out) and the echoes from this boom as it passes objects along the way will make their way back to the ears of witnesses near the source of the shot.

Take the witnesses near the steps of the TSBD. several of them heard shots from down toward the Grassy Knoll while others heard shots from the TSBD. None of them heard any shots from the Dal-Tex Building, even though there is a very good chance shots did come from there. If the muzzle blast of a rifle in the Dal-Tex was suppressed, the first sound they would hear would be the sonic boom of the bullet in front of them, then the echo of this boom as it reflected off the TSBD behind them. Then they would hear a progression of echoes coming from further down Elm St., with the closest echo arriving first. This would mean their attention would be grabbed first by a noise in their immediate vicinity and, as their attention focused, they would begin to hear the sounds returning from down range, and they would have to decide whether the shot was from above them or down range. If the final shot was an un-suppressed rifle in the vicinity of the Grassy Knoll, its very loud muzzle blast would confirm, in the minds of the ear witnesses, the origin of the shots, and they could very easily believe all of the shots were from the Grassy Knoll.

This is, in fact, the very reason high powered rifles for snipers are fitted with suppressors; that being to hide the location of the sniper and give him a chance to escape while everyone is searching for him in the wrong direction.

Do you see now how a shot originating from behind the limo can be made to appear, to ear witnesses, to have originated from the Grassy Knoll?

Edited by Robert Prudhomme
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Hi Dave

Perhaps I have not expressed myself clearly enough here.

If suppressed high powered rifles were used in some, but not all, locations in Dealey Plaza, the value of ear witness reports as to the origin of the shots is virtually worthless, as the suppressors would have the effect of making the origin of a shot appear to be coming from where the bullet ended up, not where the bullet originated from.

This fact alone should have us taking a much closer look at evaluating exactly where the suppressed shots may have originated from.

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