The Age of Electroacoustics: Transforming Science and Sound
By Roland Wittje, M.I.T. Press, 2016, 312 pages.
This book by Roland Wittje, an associate professor at Indian Institute of Technology Madras in History of Science and Technology, is a fascinating read. The author makes the reviewer’s job easier by actually stating the intended purpose of his work through a series of questions:
- What was the place of acoustics within the discipline of physics in the period, and how should the transformations of the field of acoustics be located within the transformations of the field of physics more generally?
- Did acoustics become a scientific domain of its own?
- Was acoustics seen as proper academic physics?
- What was the relationship between acoustics and the physics community at large?
- What effect did acoustics have on our historical understanding of physics at the time?
Having seen those questions on page 3, I doubted that the author would be able to explore the subject thoroughly and provide supportable answers in only 211 pages (with an additional 36 pages of notes). I was mistaken. He does a really fine job of answering all of the queries shown above. Not only does he succeed in doing so, he also provides a thought provoking, interesting book, assigning different epochs to different chapters.
After the introductory Chapter 1, Chapter 2 starts with the important works of Hermann von Helmholtz (On the Sensations of Tone as a Physiological Basis for the Theory of Music, first German edition 1863) and the third Baron Rayleigh, a.k.a., John Strutt (The Theory of Sound, 1877). This is a good starting point as these books, which are still in print today, set a basis for the study of sound at the time and even detractors seem to agree upon their value.
Chapter 3 covers the story throughout WWI. Chapter 4, the longest in the book, addresses the interwar years of the Weimar Republic. Chapter 5, the shortest, deals with how the National Socialist German Workers’ Party (NS) used electroacoustics in propaganda and warfare plans. The final chapter, 6, discusses different definitions of noise and summarizes the answers to the questions raised above.
As aptly pointed out by the author, those epochs all influenced the field of acoustics very differently. Prior to WWI, noise was considered something that existed without being worthy of study and sound was defined as only musical notes. Thus, the study of sound was the study of music and what humans can hear with their ears. As we realize today, that is a very limited view. It would exclude many areas of investigation, such as infrasound communication by elephants.
The author does a good job of putting the study of acoustics in context within social, political, academic, and industrial environments through time. He concentrates primarily on the U.K. and Europe, with a few references to the U.S. and other countries. The Weimar Republic chapter of course deals almost exclusively with Germany during that era but that focus is acceptable as Germany was then also addressing questions as to what physics was in a broader context.
When WWI began, a major shift occurred regarding the definitions of noise and sound, and the recognition of the value of studying more than musical notes as sound. The sound made by an enemy airplane was a signal to be detected, so that the bearing, elevation, and range could be determined for defensive purposes. Valuable data could also be obtained through studying the sounds produced by U-boats or long-range cannons. Suddenly what was previously ignored as irrelevant became of great interest. Noise was redefined as that which is not the intended signal. Noise abatement also moved to the forefront — making ships and airplanes quieter became very important.
WWI occurred before computers and digital signal processing were developed, so distinguishing one plane type from another was left primarily to human listeners. When using unaided human hearing, either trained or untrained individuals could be selected, depending upon the study objectives. Researchers discovered that both types of individuals gave differing results at different times in response to the same stimuli.
The implementation of electroacoustics changed the interpretation of signal characteristics, with the introduction of microphones, vacuum tube amplifiers, and visual displays. The technology of these devices was greatly advanced during WWI. The author points out a number of technical solutions to problems in electroacoustics and how they influenced the field. For example, since electronic filtering was not well developed, and microphones did not have a large dynamic range, the frequency selective Tucker’s Hot Wire Microphone was developed. Tucker’s Hot Wire Microphone, a resonant cavity with a hot wire stretched over one end whose resistance changes when vibrated by sounds at the cavity’s resonant frequency, can be made to detect sounds below 500 Hz without interference from other frequencies. This was a major advancement.
After WWI, the major commercial applications of electroacoustics were in the areas of telephony, radio, and sound motion pictures. These included microphones, loud speakers, amplifiers, and magnetic recording equipment. There was still a need to develop electroacoustics for warfare applications, but those uses were highly curtailed in Germany. For example, Germany was not allowed to have any submarines, in accordance with the Treaty of Versailles. But, by exploring the commercial uses, noise produced by the electronics became more of an issue. The author does a good job of showing how and why the noise made by electronics was discovered and addressed.
The difference and interplay in Germany between universities, industrial research laboratories, Technische Hochschulen, and public research laboratories are well described. The interactions and definitions of these separate bodies have changed over the years and the author does an excellent job of describing those institutions and the people who drove them. An understanding of these dynamics is really necessary to comprehend scientific and engineering development in Germany.
As previously mentioned, Chapter 5 — the shortest — describes the period from 1933 (when the National Socialists gained control of Germany) to WWII. It discusses changes in personnel at German organizations due to their political and Jewish connections, giving the effects upon the lives of specific individuals. It mentions technical details, such as the attempt to have massive crowds all hear the same thing at the same time for synchronized events. It is clear that once the Nazis were in control, they understood how to use electroacoustics in their propaganda program. The author contrasts President Franklin Roosevelt in the United States having fireside chats via radio to build intimacy with the American public to the German’s mammoth meetings to inflame national fervor en masse.
This chapter also addresses technological developments, including the Telefunken Löschstrahler — the extinguishing loudspeaker. This was two circular loud speakers encircling a pole (one a distance above the other) with the speakers being fed the same sounds 180 degrees out of phase. The result was that everyone within the coverage circle of the lower speaker could hear sounds broadcast by it, but those outside that circle did not hear any sound from that speaker, as the sound from the lower speaker was canceled out by the sound from the upper speaker. But those outside the coverage circle from one Löschstrahler could hear the sounds from another one.
The section within the final chapter called “Concepts of Noise and Their Diffusion” is especially good, defining, summarizing and enhancing the discussions of noise in the prior chapters in a manner that should make them intelligible to all students of signals. The author briefly mentions that signals are now often transformed into the digital domain, though that is outside the book’s time line, and he does not mention quantization noise explicitly.
Unfortunately, this book is not free of errors. For example, at one place Westinghouse is credited with developing the Vidaphone system and is said to be a subsidiary of American Telephone and Telegraph. The company that actually developed the Vidaphone system was Western Electric (then a subsidiary of American Telephone and Telegraph), which is correctly stated elsewhere in the book.