National Academies Press: OpenBook

Report of the Committee on Ballistic Acoustics (1982)

Chapter: APPENDIX E SIREN SOUNDS

« Previous: APPENDIX D POSSIBILITY OF SUPERPOSED RECORDINGS
Suggested Citation:"APPENDIX E SIREN SOUNDS ." National Research Council. 1982. Report of the Committee on Ballistic Acoustics. Washington, DC: The National Academies Press. doi: 10.17226/10264.
×
Page 89
Suggested Citation:"APPENDIX E SIREN SOUNDS ." National Research Council. 1982. Report of the Committee on Ballistic Acoustics. Washington, DC: The National Academies Press. doi: 10.17226/10264.
×
Page 90
Suggested Citation:"APPENDIX E SIREN SOUNDS ." National Research Council. 1982. Report of the Committee on Ballistic Acoustics. Washington, DC: The National Academies Press. doi: 10.17226/10264.
×
Page 91

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please APPENDIX E 89 APPENDIX E SIREN SOUNDS Two of the most conspicuous features of the Channel I recording are the complete absence of siren sounds for the first two minutes following the BRSW/WA conjectured shots and the clear presence of such siren sounds for the next 36 seconds. Several sirens are heard in succession each in turn rising and falling in intensity as would be the case if a motorcade were rapidly passing an open microphone. The siren sounds provide critical tests of both the BRSW/WA scenario and that of the Committee. The absence for two minutes of siren sounds, at a time when they should be heard, presents a serious difficulty for the BRSW/WA hypotheses. According to that scenario, the motorcycle with the open microphone was located in a precisely known position behind the President's car in the motorcade as it passed through Dealey Plaza when the President was assassinated. Many witnesses agree that sirens were activated shortly after the final shot and as the motorcade speeded up for its dash to Parkland Hospital. The complete absence of siren sounds for two minutes is difficult to explain on this scenario, and the sounds, when they do appear do not seem appropriate for a motorcycle in the motorcade, or even one catching up to the motorcade. If Officer McLain had the open microphone, it is particularly surprising that he picked up no siren sounds while accompanying the motorcade to the hospital but, at the same time, his microphone was so sensitive that it could pick up the Channel II cross talk from a nearby vehicle. The absence of siren sounds for two minutes is fully compatible with the Committee's scenario, which does not require the open microphone to have been in the procession. James Bowles' hypothesis that the motorcycle was at the Trade Mart can be supported by reasonable arguments but there is use the print version of this publication as the authoritative version for attribution.

About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please APPENDIX E 90 no firm evidence for that location. Although the two-minute absence of the police sirens is obviously compatible with the Committee's scenario, the timing of the appearance of the sirens requires careful examination. The cross correlation between the “hold everything...” phrases on Channels I and II provides a relative timing of events that can be tested for reasonableness with respect to the siren sounds. Absolute times were obtained by running Channels I and II from the original Dictabelt and audograph disk, with the speeds adjusted to provide the correct frequency for the 60 Hz hum on the original recordings. In this operation it was found that “hold everything...” on Channel I begins 123 seconds before the siren sounds and on Channel II there is 64 seconds of continuous recording between “...Go to the hospital...” and “hold everything...” which gives 187 seconds between “...Go to the hospital...” and the beginning of the sirens. Since the distance from the assasssination site to the Trade Mart is 2.273 miles, this corresponds to an average speed of 43.8 miles per hour if the trip began at the time of “Go to the hospital”. At first consideration this appears to be surprisingly slow for a trip to the hospital, but there were turns, traffic, a heavy car, Mrs. Kennedy and a Secret Service Agent crawling over the back of the car, and a critically wounded passenger to slow the average speed. The speed we estimate is compatible with the testimony of Agent Greer, the driver of the President's car, in volume II page 121 of the Warren Commission Report3: “...I was getting through traffic and through streets as fast as I could get through... I would estimate that I must have been doing between 40 and 50 at least 50 miles per hour at times. We might have been going as fast as 50 miles an hour I am sure....” If one assumes that on the streets and access ramps the average speed is 40 miles per hour, that the average acceleration in a turn is 0.2g, and that the Zapruder film gives the time to leave Dealey Plaza, the above 187 seconds would require an average speed on the Stemmons Freeway of 58.5 miles per hour, which seems reasonable in view of Agent Greer's testimony. It should be noted, however, that there is considerable uncertainty as to the speeds attained, the location of the open microphone, and the time following the assassination at which the “Go to the hospital” was broadcast. Although this discussion shows the compatibility of the use the print version of this publication as the authoritative version for attribution.

About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please APPENDIX E 91 “...hold everything...” identification with the known firm data, it should not be misinterpreted as a proof of this interpretation or as a reliable determination of the location of the vehicle with the open microphone, since there is considerable uncertainty as to speed of the vehicle. There is also contradictory evidence about the time interval between the assassination and the “Go to the hospital....” As this time is lengthened the average speed is reduced. However, it should be noted that the assumption of a long time interval makes more acute the difficulty with the BRSW/WA scenario discussed in Appendix C. use the print version of this publication as the authoritative version for attribution.

Next: APPENDIX F POSSIBLE FURTHER STUDIES »
Report of the Committee on Ballistic Acoustics Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

At the time of the assassination of President Kennedy, the Dallas police recorded sounds from an open microphone; these sounds have been previously analyzed by two research groups at the request of the House Select Committee on Assassinations. Both groups concluded with 95% probability that the recordings contained acoustic impulses which provide evidence for the existence of a shot from the grassy knoll area of Dealey Plaza. On the basis of these results and since shots definitely were fired from the Texas School Book Depository, the House Committee concluded that "scientific acoustical evidence establishes a high probability that two gunmen fired at President John F. Kennedy."

Report of the Committee on Ballistic Acoustics studied these reports and the Dallas Police recordings on which they are based. This book reviews the methodology employed in the evaluations of the recorded acoustic data and of the conclusions about the existence of a shot from the grassy knoll. According to this report, the acoustic analyses do not demonstrate that there was a grassy knoll shot, and in particular there is no acoustic basis for the claim of 95% probability of such a shot. The acoustic impulses attributed to gunshots were recorded about one minute after the President had been shot and the motorcade had been instructed to go to the hospital. Therefore, reliable acoustic data do not support a conclusion that there was a second gunman.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!