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The Absolute Sound
Issue 230   February 2013
Back To The Future
Editorial By Robert Harley

   

TAS Issue 230   February 2013  We've become 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.

So 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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