This article was originally published in the February 2000 issue of Sound & Communications.
In this series of articles, we will document the lives and achievements of some of the giants in our community and in the sciences that support it. Many of these prominent pioneers are no longer with us, so in most cases we’ll rely on secondary sources for documentation of their achievements. The names of men of science and technology such as Fletcher, Wente, Maxwell and Olson have ceased to be everyday words and their contributions have been ignored or forgotten. However, in their time they guided the fledgling sound industry into the vast commercial and consumer business which is now an ever-present element in our lives. As Don Davis once said, “Truly, we stand on the shoulders of giants.”
It is astounding when you consider that the audio industry changed from essentially a primitive, mechanics-based discipline in 1920 into a significantly sophisticated and developed electronics field by the 1930s. Within the span of a decade, radio broadcasting, recording, “talkies” and their attendant technologies transformed the worlds of entertainment and communications.
Sound in Antiquity
The subject of acoustics was a familiar theme in the philosophical writings of the Greeks as early as the 4th Century B.C.E. Being of a philosophical bent, the Greek writers tended to wax eloquent on the abstract elements of their subject, but without engaging in any real scientific observations. This fascination with acoustical properties continued into the Roman Era, when the Roman architect Vitruvius employed rudimentary principles of acoustics to the stadiums and amphitheaters of his time and fellow Roman Lucretius explored the concepts of reverberation.
After the fall of the Roman Empire, the flicker of acoustical knowledge was carefully fanned and nurtured by Arabic scientists. We owe a great deal of our knowledge of acoustics to Islamic scholars Al-Kindi and Al-Farabi, who translated the earlier Greek works and made their own contributions to the advancement of the acoustics discipline.
Investigation and experimentation in Western Europe resumed during the Renaissance in Italy, France and Germany, whereupon the study of acoustics was vigorously explored. These phases of the development of acoustics in antiquity are very well covered in Frederick Hunt’s Origins in Acoustics, which traces the development of acoustical science from its earliest premises up until about the time of Isaac Newton.
The subject of acoustics was a familiar theme in the philosophical writings of the Greeks as early as the 4th Century B.C.E.
Drawing on manuscripts prepared by Hunt and published after his death in 1972, this well researched and annotated volume is probably one of the best historical references in the field. In Hunt’s book we are led from the philosophical musing of the Greeks through the Age of Experimentation and into the Age of Scientific Reasoning. Hunt apparently had every intention of carrying his work forward to cover the Modern Era, but the effort ended with his death.
As Hunt has already covered the early times, this series of articles will focus on those pioneers who contributed to the development of sound and communications from the era of Newton forward.
Rayleigh – A Biographical Sketch
With the republication of Lord Rayleigh’s book The Theory of Sound by Dover Publications in 1945, Hunt undoubtedly thought the subject had been adequately covered, and while he acknowledged Rayleigh’s work, he did not elaborate further. So we will commence with Rayleigh and then move into what we call the “modern” age.
Lord Rayleigh was born into a family of landed English gentry on November 2, 1842, in Langeford Grove near Maldon, Essex. Christened John William Strutt, he later ascended to be the 3rd Baron (Lord) Rayleigh – the name that we most frequently associate with his works.
For the time, while men of science were often elevated to peerage, it was rare that a peer by inheritance would concern himself with scientific matters. After a classical education in physics and mathematics, he graduated from Cambridge University in 1865.
‘The only merit of which I personally am conscious is that of having pleased myself by my studies and any results that may have been due to my researches are owing to the fact that it has been a pleasure to have become a physicist.’
After a rather unusual tour of the U.S. in 1868 (it was much more common for well-heeled graduates to tour the Continent), Strutt made contact with a number of American physicists with whom he maintained regular contact during his later work. Returning home, he immediately set up a physics laboratory at Terling Place, his family’s estate.
As a physicist with a wide range of interests, he probed many aspects of classical physics. At the time, there was scant equipment available to delve into what we might now consider applied physics, so Rayleigh’s lab was a collection of rather crude equipment.
Upon the untimely death of Maxwell and the declining of the appointment by Lord Kelvin, Rayleigh was called to serve his alma mater as head of the Cavendish Laboratories at Cambridge, which he did from 1879 to 1884. During this period he published some sixty scientific papers and revisited some earlier experiments to define the absolute values of the ohm, ampere and volt. These studies greatly influenced his support of a standards laboratory, which in turn led to the establishment of the National Physical Laboratory at Teddington.
At the conclusion of this tenure, he returned to Terling Place to devote himself to the independent study of physics. Except for an occasional lecture session in London and his appearances at Scientific Society meetings, he remained at his lab until his death in 1919.
Far from being a recluse, however, he involved himself in a number of activities with various scientific organizations and carried on a spirited correspondence with other scientists of the period. A prolific writer, he authored 466 scientific papers during his career. His first paper was published in 1869 and his final paper appeared in 1920, a year after his death. While he concerned himself with many elements of physics, the subjects of acoustics and optics occupied a large portion of his time.
‘The history of science teaches only too plainly the lesson that no single method is absolutely to be relied upon, [and] that sources of error lurk where they are least expected…’
An extremely conservative investigator, he frequently cautioned his fellow physicists to explore all possible avenues of research. Speaking in Southampton in 1882 to the Mathematical and Physical Science Section of the British Association upon his assumption of the presidency of that organization, he cautioned, “The history of science teaches only too plainly the lesson that no single method is absolutely to be relied upon, [and] that sources of error lurk where they are least expected…”
Rayleigh was elected a Fellow of the Royal Society in 1873 and served as the body’s president from 1905 until 1908. In addition to his other accomplishments, he was awarded the Nobel Prize in 1904 for his discovery, with Sir William Ramsay, of the inert gas
Strutt was awarded the Order of Merit in 1902. His acceptance speech speaks volumes about the modesty of the man: “The only merit of which I personally am conscious is that of having pleased myself by my studies and any results that may have been due to my researches are owing to the fact that it has been a pleasure to have become a physicist.”
In what might seem by today’s standards to be a whimsical study, he explored how wavelengths and particles serve to make the sky blue. This set the stage for a more solid understanding of wavelengths and the diffraction of light. In two separate papers prepared for the Philosophical Magazine in 1871 and 1899, he explored and defined the phenomena of light frequency and polarization.
The Theory of Sound
Along with his other concerns, Rayleigh turned his attention to the physics of acoustics and published his Theory of Sound in 1877/78. Building on the work of Helmholtz, published in German 15 years earlier, Rayleigh defined the principles of the propagation, scattering and diffraction of sound. This work laid the foundation for the practical application of sound propagation and for the (yet to be developed) operating characteristics of loudspeakers.
A page from one of Rayleigh’s notebooks.
In 1868, Sir George Stokes published a paper that declared that sound radiation could be materially increased by preventing the circulatory flow of air around the edges of a vibrating surface – thereby giving rise (eventually) to the concept of an infinite baffle for a loudspeaker. A few years later, Rayleigh, citing Stokes’ earlier work, presented what to this day is the classical physics definition of sound radiation from a rigid piston vibrating in an infinite baffle.
Hunt could just barely conceal his amusement as he described how the loudspeaker designers of the 1920s strove mightily to reinvent the wheel. He wrote, “The surprise with which one worker in this field (loudspeaker development) after another tardily discovered Rayleigh’s analysis of the baffle problem may possibly have been related to the fact that by 1920 the second (1894) edition of Rayleigh’s Theory of Sound had been out of print for a long time. The reprinted edition of 1926 appeared in time to become better known to the following generation, but not in time to help the various experimentalists who discovered baffles before they discovered Rayleigh.”
Among his other contributions to acoustics, Rayleigh conceived and designed the first instrument that could accurately measure the true intensity of sound. Rayleigh’s two-volume work on acoustics and sound propagation was published at a point in time when Alexander Graham Bell and Thomas Alva Edison were in the process of developing the telephone and the phonograph (respectively). So, Rayleigh’s work was not the obscure musings of a “gentleman scientist,” but a major contribution to the development of devices which today we take for granted.
Rayleigh was to remark in his Presidential Address to the British Association’s 1884 meeting in Montreal on the subject of the development of the telephone and the phonograph, “The beautiful inventions of the telephone and the phonograph, although in the main dependent upon principles long since established, have imparted a new interest to the study of acoustics. The former, apart from its uses in everyday life, has become in the hands of its inventor, Graham Bell, and of Hughes, an instrument of first-class importance. The theory of its actions is still in some respects obscure, as is shown by the comparative failure of the many attempts to improve it…”
Building on the work of Helmholtz, published in German 15 years earlier, Rayleigh defined the principles of the propagation, scattering and diffraction of sound.
The observations and calculations made by Rayleigh in 1877/78 have stood the test of time and are cited to this day in physics texts that cover acoustical propagation. A further testimony of the staying power of Rayleigh’s work is the fact that Dover Publications (New York) saw fit to republish his Scientific Papers (six volumes bound as three) in 1964.
At the age of sixty, when most men might have considered their contributions to science as having reached a conclusion, Rayleigh revisited his earlier works, and between 1903 and 1919 he authored an additional 90 papers on the subjects of acoustics and optics. Among these important papers, several of the ones on acoustics addressed the subject of binaural sound and the directionality of human hearing. In 1907, Rayleigh published a paper on the phase relationships of sound as they applied to the physiological and psychological reception of sound. His final paper, “Resonant Reflections of Sound from a Perforated Wall,” was issued in 1919 and published after his death in 1920.
Lord Rayleigh was the first to define, comprehensively, the physics and characteristics of sound. Admittedly, his works are heavily reliant on calculus, and the non-mathematical reader may find the text daunting. However, the introductory notes to his thesis are very informative for all.
If there is any “hinge of history” dividing early acoustical experimentation and the rapid development of audio products, it is the development of the vacuum tube and electronic amplification. Rayleigh and the scientists of his era had to make do with mechanical (or at best, electromechanical) contrivances in conducting their work. Electricity was, of course, a well-known subject at that time, but still in a semi-primitive state, as evidenced by the fact that Rayleigh had to redefine the relationships between the basic electrical units of measure. The use of electricity to solve acoustical problems would have to wait a little longer.
- Beranek, Leo L., Acoustical Measurements, MIT Press, 1949 and revised edition, Acoustical Society of America, 1988.
- Hemholtz, H. L. F., Die Lehre von den Tonempfindungen als physilogische Grundlage fur die Theorie der Musik, first edition, Springer-Verlag, Brunswick, Germany, 1863. English translation by A. J. Ellis, On the Sensation of Tone, second edition, 1885.
- Hunt, Frederick Vinton, ElectroAcoustics – The Analysis of Transduction and its Historic Background, the Acoustical Society of America, 1954 (second printing, 1982).
- Hunt, Frederick Vinton, Origins in Acoustics, Yale University, 1978 and the Acoustical Society of America, 1992 (ISBN 0-300-02220-4)
- Pierce, Allan D., Acoustics – An Introduction to its Physical Principles and Applications, McGraw-Hill, New York, 1981 and reprinted edition, the Acoustical Society of America, 1989.
- Stokes, Sir George G., “On the Communication of Vibration from a Vibrating Body to a Surrounding Gas,” Trans. Phil. Roy. Soc., London, 1868.
- Strutt, John Williams, 3rd Baron (Lord) Rayleigh, The Theory of Sound, 2 volumes (I) 1877 and (II) 1878, MacMillan & Co., Ltd., London. Second Edition, 1894. Subsequently republished, 1926, 1929, and published as a single volume by Dover Press, New York, 1945.
- Strutt, John William, 3rd Baron (Lord) Rayleigh, Address to the British Association, Montreal meeting (1884), B.A. Report, Montreal 1884, pp 1-23.
- Strutt, John William, 3rd Baron (Lord) Rayleigh, “On Our Perception of Sound Direction,” Phil. Mag. xi, pp 97-108, 1906.
- Strutt, John William, 3rd Baron (Lord) Rayleigh, “Acoustical Notes VII, Sensation of Right and Left from Revolving Magnets and the Telephone,” Phil. Mag. xiii, pp 316-333, 1907.