Recording - September 2013 - Cover3

Now, while this probably seems trivial by today’s standards, we have to
remember that what was being demonstrated here wasn’t just one new
technology. First there were wideband microphones capable of reproducing nearly the full frequency range and dynamics of the orchestra. Second
and equally important were wideband speakers with that capability.
Third, this was the first time anyone had ever sent wide frequency ranges
that distance over telephone lines; special carrier electronics had to be
constructed. Fourth and not least: this was three-channel stereo, the first
time anyone had ever really heard stereo outside the laboratory.
It was intensity stereo; three omnidirectional microphones across the
orchestra driving three directional speakers across the state in
Constitution Hall. With wide spacing like this, it’s as if a metal plate has
been put across the stage with three holes in it. As sound passes from the
instrument to the listener, phase relationships between the two ears are
lost; all that is maintained are the amplitude relationships between the

Guest editorial by Scott Dorsey

Thank Ma Bell
When audio was shiny and new, a huge
amount of the very early fundamental
research on audio transducers and transmission was performed by the telephone
company. It seemed a natural extension
of their main business; in the 1930s, both
sound films and electrical disc recording
were in great part developed and marketed by Western Electric, the manufacturing division of Ma Bell.
With these markets exploding and with
so much about electrical transmission,
transducers, and human hearing still
unknown, it seemed just good business
sense for Bell Laboratories to put a huge
amount of work into basic research in the
field. Just leafing through 1930s issues of
the Bell System Technical Journal (which
you can now do online courtesy of AlcatelLucent, which owns the remains of the Bell
research arm—check out www3.alcatellucent.com/bstj/ for a complete archive),
you will find a wild and amazing list of
papers on a wide swath of subjects relevant to the growing telephone industry.
There are papers on microphone and
speaker design and on human perception
of audio, interspersed with papers on telephone switching systems, operator fatigue,
and even what kinds of wood make the
best telephone poles.
On April 27, 1933, a day which should
surely be celebrated as a holiday in the
audio industry, engineers from Bell Labs
gave a public demonstration of the fruits
of this research. The Philadelphia
Symphony Orchestra, conducted by its
Associate Conductor Alexander Smallens,
performed in the Academy of Science Hall
to rows of empty seats... and to three
microphones, which were run to three
speakers on the stage of Constitution Hall
in Washington, DC, where the Symphony’s
Conductor Leopold Stokowski supervised
the playback.
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RECORDING September 2013

two ears. This type of stereo restricts the sort of imaging possible, and the
Bell Labs folks discussed that.
What is fascinating about this is that every single aspect of the pickup
and reproduction was very carefully engineered by the Bell Labs scientists; so many things today that we take for granted in the world of audio
technology were still being investigated. This includes everything from the
basic physics of hearing to the operating principles of microphones and
loudspeakers.

Amplifying equipment
used in the 1933
Philadelphia concert.
The taller racks are 8'
high and contain A1
and A2 amplifiers,
volume indicators,
and various controls.
The details of the work were summarized in a set of six papers from Bell
Labs engineers which appeared in the January 1934 issue of Electrical
Engineering. In 1964, Paul Klipsch made a point of reprinting this set of
articles through the Audio Engineering Society, stating, “Fundamentals
do not change. The laws of physics endure. In reprinting the Symposium,
the fundamentals are restated.”
In 2002, Jay McKnight, the chair of the the AES Historical Committee,
scanned this material into digital form, tracked down the original rights, and
made this set of papers available on the AES historical website under the
title “Symposium on Auditory Perspective.” It’s still there and free for the
taking—the PDF is downloadable from www.aes.org/aeshc/docs/bell.labs/
auditoryperspective.pdf—and it’s absolutely worth reading if you have any
curiosity into just how all of this stuff really works at a fundamental level.
No math beyond high school algebra is needed (unless you want to read the
appendix on slit-loading of loudspeakers). And if you don’t come out of it having learned something useful, you can always ask for your money back.
Scott Dorsey (dorsey@recordingmag.com) is an audio engineer and
enthusiastic student of the history and technology of recorded sound.
As we’ve frequently noted in our pages, he eats this stuff up.

http://www3.alcatel-lucent.com/bstj/ http://www3.alcatel-lucent.com/bstj/ http://www.aes.org/aeshc/docs/bell.labs/auditoryperspective.pdf http://www.aes.org/aeshc/docs/bell.labs/auditoryperspective.pdf

Recording - September 2013

Table of Contents for the Digital Edition of Recording - September 2013