The Kennedy Assassination Tapes
A Rebuttal to the Acoustical Evidence Theory
James C. Bowles






As it would appear, since the Channel 2 dispatcher gave the 12:30 time and station check, "12:30 KKB364" a few seconds before Chief Curry's broadcast, "We're going to the hospital . . . ", the assassin's shots were fired either just before or immediately after 12:30 p.m. (Channel 2). However, that would be an inaccurate assumption.

There is a simple way to determine more accurately the approximate time the 12:30 station check was actually given.


The Channel 2 dispatcher acknowledged the chief's location at Main and Lamar Streets, giving the time as 12:28 (Channel 2). About 30 seconds later, the chief stated he confirmed this message and again gave the time as 12:28 (Channel 2). Assuming that the first "12:28" was stated at exactly 12:28, the second would have been given at 12:28:31. At that time, the chief was westbound on Main Street, and the President's limousine was several seconds distance behind him.

The chief traveled the remaining distance to Houston Street and turned right, or north, and traveled approximately 220 feet to its intersection with Elm Street. At Elm, the motorcade turned left to the west toward the Triple Underpass. That last turn involved an acute angle (120 degrees) and it could not be negotiated rapidly, especially in the existing crowd. The chief drove west on Elm Street before announcing his location as the ". . . Triple Underpass. . . ."

Since the 12:28:31 (Channel 2) position check at Main and Market Streets, the lead-car in the motorcade had progressed some 900 feet, including two turns. The escort officers and supervisor estimated that the motorcade was traveling at "walking speed" or about 3 to 4 MPH. It would require 2 minutes and 22 seconds to cover the course. That would place the chief at the point where he announced "Triple Underpass" no earlier than 12:31:04 (Channel 2). At that time, Chief Curry was about midway between Houston Street and the underpass. With the President's limousine several seconds behind the chief, the President was approaching his final turn and about to come into the assassin's sights.

Approximately 12 seconds after the chief's message, the dispatcher gave the station check. Actually, the 12:30 station check was given more nearly at 12:31:16 (Channel 2).


Chief Curry announced his location as being at the Triple Underpass at approximately 12:31:04 (Channel 2) while traveling west on Elm, midway between Houston and the underpass. The President's limousine, slowly approaching the intersection to negotiate its turn, would soon be following the chief. Projecting that the limousine completed its turn a couple of seconds later and accelerated to approximately 11 MPH as suggested by the Zapruder film, the limousine would have been in the position where the first shot was fired by 12:31:10 (Channel 2) or 12:30:55 (Channel 1). Allowing 8.3 seconds for all shots (the interval developed by the Select Committee) the shooting ended by 12:31:18.3 (Channel 2) or by 12:31:03.3 (Channel 1).

There was a slight hesitation in the progress of the motorcade. Officer Chaney raced forward to tell Chief Curry that President Kennedy had been shot. The chief then ordered the escort officers to proceed to the hospital. His orders were given on Channel 2 a few seconds after the 12:30 time check, or just after 12:31:16-17. Therefore, determining that the shooting had concluded by 12:31:18-19 (Channel 2) and by 12:31:03-04 (Channel 1), and then adding some 4 or 5 seconds for the hesitation, the motorcade would have begun leaving Dealey Plaza at approximately 12:31:08 (Channel 1). This determination of "time" matches with Channel 1 time when the officer working beat #38 observed the motorcade leaving Dealey Plaza. (See that section, this chapter.)


There is a conflict between the committee's determination of a time-fix and that determined in this text. The Committee's estimate of a time-fix is 16.7 seconds earlier than that in this text.



Bell tone - Text    12:31:20.0   
Bell tone - Committee*    12:31:03.3   
Difference    - 16.7 sec.   


*Seven seconds after the last shot or 12:30:55.3 Committee time.


Next, adjust the shooting times projected by the Committee according to their impulse patterns with the time differences in this text:

Shooting Time - Committee 12:30:47.0 thru 12:30:55.3
Less Difference -16.7                       -16.7
Committee time - Adjusted      
To Text Time 12:30:30.3 thru 12:30:38.6

Now, contrast the shooting times projected by the Committee, and adjusted for the 16.7 second difference, with the shooting times established through reconstruction:

Shots - This Text      12:30:55.0 thru 12:31:03.3 (Ch. 1)     
Shots - Committee      12:30:30.3 thru 12:30:38.6 (Ch. 1)     
Difference 24.7                     24.7 seconds


Allowing for a time-fix error of 16.7 seconds and an adjustment in the shooting times of 24.7 seconds, the conclusions here a built-in error of some 51.4 seconds. The Select Committee found its acoustical evidence approximately one minute BEFORE the shots were fired!

At the time established by the Committee, the President was just ending his turn from Main Street to Houston Street. He would still have to travel Houston Street, turn onto Elm Street and travel some 100-plus feet.


Consider the route to the hospital in measured segments as follows:
(See Appendix, Illustrations V, VI, and VII. )


A - Assassination site to Elm and the on-ramp to Stemmons Freeway . . . 800'
B - On-ramp, Elm to northbound Stemmons . . . 800'
C - Stemmons, north, on-ramp to Continental . . . 1475'
D - Stemmons, Continental to Oak Lawn . . . 6000'
E - Stemmons, Oak Lawn to Industrial via off-ramp . . . 2925'
Recap: Dealey Plaza to Trade Mart (2.273 mi) . . . 12000'
F - Industrial, Stemmons service road to Harry Hines . . . 1600'
G - Hines, north to Amelia . . . 2075'
H - Hines, north, Amelia to hospital drive . . . 900'
I - Hospital drive, Hines to emergency dock . . . 1150'
Recap: Trade Mart to Parkland (1.084 mi) . . . 5725'
Total -Dealey Plaza to Parkland . . . 17725'



Dealey Plaza to the Trade Mart
SEG.      DIST.      SPEED      SECONDS      12:21:08 (Ch 1)     
A 800' 50 10.91 12:31:18.91
B 800' 55 9.92 12:31:28.83
C 1475' 70 14.37 12:31:43.20
D 6000' 85 48.13 12:32:31.33
E 2925' 70 28.49 12:32:59.82 (Trade Mart)
  12000' 73.2 111.82  

Dealey Plaza to the Trade Mart
F      1600'      65      16.78      12:33:16.60     
G 2075' 70 20.21 12:33:36.81
H 900' 65 9.44 12:33:46.25
I 1150' 40 19.60 12:34:05.85 (Hospital)
  5725' 59.14 66.03  
Total 17725' 67.98 177.85 Dealey Plaza to Parkland



The motorcade's projected arrival time at Stemmons and Industrial, the Trade Mart, is 12:32:59.82 (Channel 1). The sound of sirens began to be audible at 12:33:01.02 (Channel 1). Accordingly, the motorcade reached the Trade Mart at the time the siren sounds began to appear. This, and the fact that there were no other emergency vehicles operating in the city, more especially, not as a group, tends to corroborate that the open mike received the siren sounds at that time and place and no other.

The motorcade's projected arrival time at Parkland Hospital emergency dock is 12:34:05.85 (Channel 1). Adding a 15-second adjustment converts this to 12:34:20.85 (Channel 2). Chief Curry's last radio messages were on Channel 2 in the 12:34 time frame, and before 12:35.

The confirmation of arrival time at the Trade Mart and at Parkland Hospital confirm both the speed estimates for the motorcade, and the projected time-fix for the Channel 1, open mike episode starting at 12:29:10 p.m.

Committee counsel suggested that Officer McLain left Dealey Plaza ". . . later than he remembered." Thus the siren sounds were picked up by his radio as ". . . he caught the motorcade." For that to have occurred, McLain would have covered the entire route at speeds greater than possible. If he covered segments "A" and "B" at 60 MPH, segments "C" and "E" at 75 MPH, it would require that he cover the 6000' segment "D" at an average speed of 93.9 MPH. To have averaged that speed, he would have exceeded 100 MPH peak speed. That is impossible for a motorcycle with a top speed of 85 to 90 MPH. Furthermore, having been operated at such a slow speed for so long a time, the motorcycles were running hot, and were carboning-up. That inhibits their performances momentarily. The above tends to disprove the Committee counsel's explanations that McLain caught and either passed or fell behind the main body of the motorcade, thus explaining why the siren sounds began to appear, then disappear.


During the 12:28 (Channel 1) time frame, the officer working beat #38 was southbound on Stemmons from Industrial. He was en route to Municipal Court by way of Stemmons to the Triple Underpass, then east on Commerce Street to City Hall.

At 12:33 plus, he informed the dispatcher of pedestrian traffic crossing Stemmons Freeway near the Marriott Motel, and suggested that the dispatcher inform the command post at the Trade Mart. The dispatcher acknowledged #38 and asked whether he was still en route to court. The officer acknowledged that he was. It was at this point that this text fixed Channel 1 time as 12:29:10 p.m., and the motorcycle microphone opened and remained open for more than 5 minutes.

The officer working #38 concluded his message as he approached Oak Lawn on Stemmons. He continued south to the off-ramp for the Commerce Street lanes of the Triple Underpass, eastbound. On exiting the freeway service road and starting east on Commerce, his attention was attracted ahead and to his left by the motorcade coming through the Triple Underpass, traveling west in the Elm Street lanes with their red lights on and their sirens "screaming."

The distance traveled from where he ended his message, to where he observed the motorcade is approximately 10,000 feet. His speed was about 55 to 60 MPH on the freeway and about 20 MPH on the off-ramp. After stopping at Commerce Street, he started east traveling some 150 to 200' at a speed of 30 to 35 MPH. At that point he saw the motorcade as described. His average speed was near 55 MPH over the course. Accordingly, it would require some 2 minutes, 4 seconds to drive the 10,000 feet. Starting at 12:29:10 (Channel 1) he would have observed the motorcade at approximately 12:31:14 (Channel 1).

This compares quite accurately with this text's estimate that the shots were fired, between 12:30:55 and 12:31:03, and when the motorcade departed for Parkland Hospital, 12:31:08 p.m. (Channel 1). This allows the front of the motorcade some 6 seconds to reach and pass through the underpass to be observed by the officer working #38. By confirming the departure time, we tend to confirm the times the motorcade reached Continental to be observed by Officer "H," and the times it would reach the Trade Mart and Parkland. Likewise, it tends to confirm 12:29:10 as the time Channel 1 experienced the open mike episode.


Starting at approximately 12:31:01 and lasting until 12:33:34 the Channel 1 radio recorded 33 seconds of the sound of several sirens.

During #91's request for a lunch mark-out (a signal 5) the sirens became audible, starting faintly at first, and increasing in loudness until about the 7th second when it reached its first peak. A second series of sirens reached its peak at about 15 seconds, and a third group at 21 seconds, and a last not quite so loud as the first, at 28 seconds. By the 33rd second, the siren sounds had faded to inaudible. It appears that there are three distinct groups with a last vehicle as fourth. Several officers stated that a lone Secret Service Car was the last vehicle in line, a little behind the others as the motorcade passed the side of the Trade Mart, eastbound on Industrial Boulevard.

In addition to distinct peaks of loudness, the peaks are accompanied by an instant of sound-blank (silence) as the peaks appear to be passing the open microphone. This is referred to by scientists as the "Doppler Effect," which deals with changes in frequency as a sound source and a receiving source pass one another. The presence of the "Doppler Effect" scientifically indicates that the sound sources (the motorcade vehicles) were passing a receiving source (the open microphone) as opposed to an open microphone passing the several sound sources. The open mike could not have been passing the sound sources as the engine on the motorcycle containing the open mike could be heard running at idle-speed. It was sitting still, stopped on the Industrial Boulevard side of the Trade Mart, north of the command post, near the motor pool. As the motorcade turned east on Industrial toward Hines, they passed the subject motorcycle.

The motorcycle was approximately 80 to 100 feet east of the east curb of Stemmons Service Road. After completing their turns onto Industrial, the motorcade vehicles had 100 to 150 feet in which they would accelerate to between 50 to 60 MPH. At an average speed of 55 MPH, a motorcycle travels 80.666 feet per second. Accordingly, a few seconds after turning, the motorcade vehicles would come into the maximum pickup range of the open mike. Since each group seems to be about seven seconds in passing, they would cover approximately 565 feet in two equal segments of 282 feet each, an approaching-half and a departing-half. (See Appendix, Illustration IV.)

It is unlikely that sounds originating at distances greater than 300 feet would register with the open mike due to equipment limitations. Also, it would depend to some degree on the loudness of the sound, surrounding conditions, and the condition of the equipment. But 300 feet is the approximate maximum operating range.

With the sound approaching from the left, entering the first 282 foot segment, and the subject receiving microphone some 80 to 100 feet to the south, the sound sources would be approximately 300 feet from the receiver. As the sound sources reached the mid-point of the two segments, we find the "Doppler" exactly where it must be. Then, as the sound sources pass through the second segment in departing, the sounds fade away exactly as they must, passing out of the 300 foot range.


The motorcycle with the open microphone was at or near the motor pool, on the north side of the Trade Mart, at position "A" in Illustration IV. The motorcade passed the receiver from the receiver's left to right at an average speed of 55 MPH, and traveled 565 feet in passing the receiver. This condition caused the sound sources to pass at the optimum distances at which they were recorded, including exactly where the "Doppler" would be, and at the exact time that it should have, 12:33:01 to 12:33:34 p.m., Channel 1 time. This could have been confirmed by the Select Committee's investigation but they declined.


Several three-wheel officers, assisted by relief officers, were assigned to work major intersections on the motorcade route along Cedar Springs Road and on Harwood Street to Main Street. One of these, Officer "K," completed his assignment about 12:23 (Channel 1) and left on his 2 1/4 mile trip to the Trade Mart where he was due to report to the motor pool by 12:30 p.m.

Shortly after he left his intersection en route to the Trade Mart, his transmitter stuck open for brief intervals during which the sound of the engine suggests a traveling speed of 25 to 30 MPH. During the 12:28 (Channel 1) time frame his mike opened again for 17 1/2 seconds. The engine speed still appears to be near 30 MPH.

Then, at the projected time of 12:29:10 (Channel 1) his mike stuck open once again and remained open for more than five minutes. During the first minute or two his speed held steadily near 30 MPH. Then, the engine sound slowed to an irregular speed for a little less than a minute.

Officer "K" left his corner with 6 1/2 minutes to travel two and one quarter miles to he Trade Mart. There was heavier traffic, a stop sign and three signal lights along the initial portion of his route. Estimating his overall trip at 25 MPH, he had no trouble arriving on time.

He went to the Trade Mart and passed time listening to a two-wheel motorcycle tuned to Channel 2. Not all three-wheel motorcycles had been furnished with two-channel radios. He, 'K," doesn't remember moving his motorcycle after he arrived. At any rate, it isn't possible to determine absolutely whether the recorded sounds of engine changes represent activity of the subject motorcycle or of other motorcycles arriving and departing, as they were doing at the motor pool. At one point in the recording the sound does seem more like the engine of a two-wheel rather than a three-wheel motorcycle.

"K" was using a relief or spare motorcycle that day, one which was not equipped with a Channel 2 radio, and one which had experienced frequent radio trouble.

Shortly after the motorcade passed the Trade Mart, Officer "K" can be heard to speak but his message cannot be understood. Moments later he started off on his motorcycle, en route to Parkland. Apparently, in checking his radio, listening to find the opportunity to transmit, he found that his radio was stuck in the transmit mode.

At Parkland, after the immediate urgency had subsided and almost everyone had departed, Officer "K" commiserated with other officers over a couple of his personal misfortunes during the day. One of these problems was that his radio had stuck open during the emergency.


Since there was no time standard for radio communications in the Dallas Police system, and since each radio dispatcher's position operated independently, and each operator performed individually, and since "time" indications could and did come from several different sources, it is impossible to fix a time reference with absolute certainty. However, to reconstruct events of the day and to show progression through and the relationship of certain events, it is necessary to establish some "time fix" to serve as a standard reference base. In this text, "time" turns on a fix at 12:29:10 (Channel 1).

Since the channels were not synchronized it was necessary to show as precise as possible a relationship. First, Channel 2's announced time was approximately 15 seconds ahead of Channel 1. To correct the difference and show the approximate "true time," 15 seconds should be added to Channel 1 times, or subtracted from Channel 2 times. These two time references when considered together, represent true or real-time as accurately as possible.

The best and easiest method for showing their relationship is through those incidents where Channel 2 messages are present on Channel 1 recordings. These events are also referred to as "cross talk." However, the reference can be misleading as it might suggest that one person was knowingly talking to another on a different channel. Such cross-talk is virtually impossible. That is, it could be done through awkward preparation, but there is absolutely no reason for doing so.

There are three occasions where the open microphone picked up portions of Channel 2 messages from outside speakers on radios which were tuned to Channel 2, and on one occasion, the Channel 2 dispatcher used his "simultaneous broadcast" capability to broadcast at once on both channels.

The relationship between Channels 1 and 2 in cross-channel recordings is as follows:

1. At approximately 12:31 (Channel 2), Deputy Chief #4 discussed a traffic problem with Captain #125. The last sentence in that message, "I'll check it," was picked up over the open mike and was transmitted and recorded at approximately 12:31:02 (Channel 1).

2. At approximately 12:34:16 (Channel 2), Motorcycle Sergeant #190 asked, "You want me to hold . . . ?" Part of his message was recorded by the open mike at approximately 12:33:52 (Channel 1).

3. At approximately 12:35:58 (Channel 2), the Channel 2 dispatcher activated the simultaneous broadcast switch to announce at once over both channels, "Attention all emergency equipment. . . ." This was recorded at approximately 12:35:38 (Channel 1).

4. At approximately 12:36:21 (Channel 2), Sergeant #260 broadcast, ". . . came from the 5th floor . . ." Most of this message was picked up and recorded at approximately 12:35:57 (Channel 1).

It must be remembered that these times are estimates based on several factors, However, it is useful to observe these events as they tend to confirm time estimates through their near relationships, and more so, that the subject motorcycle was not in the motorcade, but away from the downtown crowd and at a place where other police units were parked.


Back to the top

Next Chapter . . .

Back . . .

Table of Contents


Search this site
    powered by FreeFind

Back to archive of acoustical evidence

Back to JFK reports and documents menu

Back to JFK menu

Dave Reitzes home page