Issue 230 February 2013
Back To The Future
Editorial By Robert Harley
so accustomed to using terms such as hertz, ohms, and farads that it's easy
to forget that these values were named after the scientists who discovered
some of the fundamental properties of nature that make music reproduction
possible. We take for granted the technology of the modern world without
thinking about the insight, imagination, dedication, and long working hours
behind the discoveries on which that technology is based. It's worth looking
back on just a few of these individuals and considering how their
contributions form the foundation of audio.
The unit of frequency of electromagnetic and acoustic waves,
the hertz (abbreviated Hz), is named after the German physicist Heinrich
Hertz. His discovery of electromagnetic radiation (called "Hertzian waves"
at the time) transformed our understanding of physics and paved the way for
radio, among countless other inventions.
After Hertz earned his Ph.D. at the age of 23 he worked for
two years as an assistant to Hermann Helmholtz, after whom the Helmholtz
resonator, an acoustic absorption device, is named. Helmholtz encouraged the
young Hertz to pursue a prize offered by the Berlin Academy of Science.
Hertz's work in electromagnetics (the subject of the Academy prize) led him
to stumble on an unexpected phenomenon. Hertz had generated oscillating sparks
in an air gap and discovered that each spark produced an electromagnetic wave.
Using a loop of wire with a small gap at one end, Hertz walked around the room
and mapped the wave's shape by noticing the strength of the spark across the
gap in his wire loop. An Italian by the name of Marchese Marconi read of
Hertz' discovery and, just 13 years later, put that discovery to practical
use in the first radio transmission. Alas, Hertz didn't live to see the
practical implications of his work; he died at the age of 36 in 1894. The
number of any periodic oscillations per second, whether acoustical or
electromagnetic, are named in honor of Heinrich Hertz.
Georg Simon Ohm made only one significant contribution to
science, but it was a good one; by creating wires of varying thickness and
length he discovered, in 1827, that there was a simple, linear relationship
between the magnitude of an electrical potential (what we now call "voltage" after Alessandro Volta), the resistance of the conductor, and
the amount of current flow in that conductor. This relationship is expressed
in Ohm's Law: "The flow of current through a conductor is directly
proportional to the potential difference (voltage) and inversely proportional
to the resistance." Ohm's work was initially derided in Germany, and he
ended up losing his teaching position as a result of the criticism and spent
years in poverty. In England, however, the importance of Ohm's discovery was
recognized, and he was given the Copley Medal by England's Royal Society.
Eventually, Ohm was honored in Germany, and the city of Munich erected a
statue of him. The unit of electrical resistance is named the Ohm.
Unlike Ohm, Michael Faraday made an enormous number of
contributions, any one of which would have secured his legacy. As one of ten
children born to a laborer, with no opportunity to attend university, Faraday
was completely self-taught. He is known as the father of electrochemistry as
well as the discoverer of benzene. But our interest in Faraday concerns his
work in converting magnetic energy into mechanical motion, electromagnetic
induction, and his invention of the transformer — all essential to
microphones, power supplies, loudspeakers, and tape recorders, to name a few.
In addition to being the first scientist to create mechanical motion from
magnetic forces, Faraday had a key insight without which the modern world
would not be possible. The insight was sparked by the unexpected result of an
experiment that involved two coils of wire wound around an iron ring with a
battery attached to one of the coils. A galvanometer was attached to the
second coil. When Faraday connected the battery, the galvanometer's needle
momentarily deflected in one direction and then returned to the resting point.
When he disconnected the battery the needle momentarily jerked in the opposite
direction and returned to the resting point. Faraday had expected that the
galvanometer would indicate steady electrical current flow in the second coil
as long as the battery was connected to the first coil. Faraday made the
breakthrough of recognizing that magnetic fields were composed of "lines of
force" and that if a conductor cut through these lines of force, current
flow was induced in the conductor. Without this relative motion between the
conductor and the magnetic field, no current flow is induced. In his
experiment, the motion of the magnetic field is created momentarily as the
magnetic field expands when the battery is connected. The magnetic field is
static after it has expanded, thus no induced current. When Faraday
disconnected the battery the magnetic field collapsed, inducing a current of
opposite direction in the coil. The significance of this insight cannot be
overstated; it is the phenomenon on which all audio technology is based. The
unit of capacitance, the farad, is named after Michael Faraday.
next time you turn on your hi-fi system think of the true pioneers of audio
that made it all possible.
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