History
1.1 The mechanical
phonograph
In 1856, Édouard-Léon Scott de
Martinville invented a device based on
the basic anatomy of the human ear. It
consisted of a wooden funnel ending at
a flexible membrane to emulate the
ear canal and eardrum. Connected to
the membrane was a pig bristle that
moved with it, scratching a thin line
into soot on a piece of paper wrapped
around a rotating cylinder. He called
this new invention a “phonautograph”
or “self-writer of sound”.
Figure 1.1: The phonautograph.
This device was conceived to record
sounds in the air without any intention
of playing them back, so it can be
considered to be the precursor to the
modern oscilloscope.
However, in the
late 1870’s, Charles Cros realised that
if the lines drawn by the
phonoautograph were photo-engraved
onto the surface of a metal cylinder,
then it could be used to vibrate a
needle placed in the resulting groove.
Unfortunately, rather than actually
build such a device, he only wrote
about the idea in a document that was
filed at the Académie des Sciences and
sealed. Within 6 months of this, in
1877, Thomas Edison asked his
assistant, John Kruesi, to build a device
that could not only record sound (as an
indentation in tin foil on a cylinder) but
reproduce it, if only a few times before
the groove became smoothed.
It was ten years later, in 1887, that the
German-American inventor Emil
Berliner was awarded a patent for a
sound recording and reproducing
system that was based on a groove in
a rotating disc (rather than Edison’s
cylinder); the original version of the
system that we know of today as the
“Long Playing” or “LP” Record.
Figure 1.2: An Edison “Blue Amberol”
record with a Danish 78 RPM “His Mas-
ter’s Voice” disc recording X8071 of Den
Blaa Anemone.
Early phonographs or “gramophones”
were purely mechanical devices. The
disc (or cylinder) was rotated by a
spring-driven clockwork mechanism
and the needle or stylus rested in the
passing groove. The vibrations of the
needle were transmitted to a flexible
membrane that was situated at the
narrow end of a horn that amplified the
resulting sound to audible levels.
1.2 Magnets and Coils
In 1820, more than 30 years before de
Martinville’s invention, the Danish
physicist and chemist, Hans Christian
Ørsted announced the first link made
between electricity and magnetism: he
had discovered that a compass needle
would change direction when placed
near a wire that was carrying an
electrical current. Nowadays, it is
well-known that this link is
bi-directional. When current is sent
through a wire, a magnetic field is
generated around it. However, it is also
true that moving a wire through a
magnetic field will generate current
that is proportional to its velocity.
1
It should be said that some “recordings” made on a phonoautograph were finally played in 2008. See www.firstsounds.org for more information.
2
see “Reproduction of Sound in High-fidelity and Stereo Phonographs” (1962) by Edgar Villchur
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