IEEE Technology and Society Magazine - March 2020 - 10

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 electroac ou st ic s i n t hei r propa ga nda
pro gram. 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

IEEE TECHNOLOGY AND SOCIETY MAGAZINE

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.

Reviewer Information
Bill Liles is a Life Member of the IEEE
with degrees in Electrical Engineering, Computer Science, and Management. He holds an Amateur
Radio Extra Class license which he
uses to conduct experiments on
antennas and propagation. His
email address is lilesw@gmail.com.

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MARCH 2020

IEEE Technology and Society Magazine - March 2020

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