The siren is a source of sound (or sound transducer) which captures our attention because we know it may emanate from a police vehicle, fire engine, tornado warning tower or other danger warning system. However, there is another reason to heed the siren: it can be a “death ray”! Most of us know of the death ray from science fiction stories which describe a device which can annihilate whole armies silently from a distance. Around 1950 there were newspaper stories which heralded the advent of an actual death ray, with headlines and text such as: “‘Death Ray’ May Be Red [Soviet] Weapon. In the great super arms duel between east and west, has Russia successfully added the “death ray” to its growing arsenal?” (Franklin Johnson, OP, Washington, February 17, 1953) and “US sound ray kills mice in minute. The United States Army has announced the development of a supersonic death ray that kills mice in one minute. In spite of precautions the ray has inflicted burns, dizzyness and loss of balance on laboratory workers.” (American journal, New York, 1947). It may be assumed, and in some cases known, that the death ray referred to in these articles was a high intensity siren which was “silent” because it operated at a frequency above the threshold of human hearing (humans cannot hear frequencies above about 20,000 cycles per second). It was “high intensity” because it operated at a power level which was 10,000 times louder than the level of sound where the sense of “loudness” disappears and pain sets in; at the much louder level, pain becomes death, at least for mice.
A likely cause for the news articles was research with a siren undertaken by acousticians C. H. Allen and Isadore Rudnick, working under H. K. Schilling, Director of the Pennsylvania State College Acoustics Laboratory in 1946. Anyone who knew Izzy Rudnick would hypothesize that his response to the news articles would have been “Rumors of my death ray have been greatly exaggerated”. Indeed, a mouse had to be within about four inches (about 10 centimeters) of the siren in order to be killed, and its death was deemed to be a result of an increase in the temperature of the mouse due to absorption of the sound. In the same manner, the siren was used to heat a cup of coffee, ignite a ball of cotton and pop popcorn. The figure below shows the “trumpet horn” shaped opening of a siren, above which a glass tube is suspended; the lower part of the glass tube contains some popcorn kernels, and the upper part shows some popcorn popping upward.
At close range, a high intensity siren could cause human inner ear problems and deafness, and could set your hair on fire, but it could never be a real death ray. For the most part, the siren has received serious study by acousticians so as to make it a more efficient and longer range danger warning device.
Figure. A high intensity acoustic siren being used to pop popcorn.
J. D. Maynard
Department of Physics
The Pennsylvania State University
University Park, PA 16802
Popular version of paper 2aID11
Presented Tuesday morning, October 28, 2014
168th ASA Meeting, Indianapolis