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Dr. John Varriano Dr. Ted Clarke Jonathan Fili Department of Physics

Electricity & Magnetism: Music to Our Ears. Dr. John Varriano Dr. Ted Clarke Jonathan Fili Department of Physics Christian Brothers University. TAAPT Annual Meeting March 22 , 2014 Oak Ridge High School. 1. Electric “Guitar”. Physics. electromagnetic induction ac circuits

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Dr. John Varriano Dr. Ted Clarke Jonathan Fili Department of Physics

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  1. Electricity & Magnetism: Music to Our Ears Dr. John Varriano Dr. Ted Clarke Jonathan Fili Department of Physics Christian Brothers University TAAPT Annual Meeting March 22, 2014 Oak Ridge High School

  2. 1. Electric “Guitar” Physics • electromagnetic induction • ac circuits • standing waves • musical scale Materials • small coil with lots of turns (e.g. coil from a relay) • small magnet (neodymium) • steel wire • wood, screws • hook-up wire, connectors, soldering iron, solder • amplifier, speaker, audio cables

  3. Coil resistance  200-400  relays

  4. Simple Design washer & screw washer & screw coil/magnet wire connectors bridge magnet wire coil

  5. More Elaborate Design wire wire magnet magnet tuning peg finger board bridge

  6. Characterizing Coil Measure resistance with meter. R = 202  Determine inductance using impedance method. f = 500 Hz R Vrms = 4.00 V A f Vrms C coil V L Irms = 3.00 mA Vrms Irms Irms L  0.42 H Z = = 1333  typical guitar pick-up coils R = 5-10 k, L = 1-9 H, C=1 nF

  7. Fret Bars? 12-tone equal temperament Lm dm octave nut L0 f0 f1 f2 f12 = 2f0 bridge (2) (3) Combining (1), (2), (3) gives (1)

  8. Coil Voltage Output (before amplification)

  9. Coil Voltage Output Fast Fourier Transforms Microphone Voltage Output (Placed in Front of Speaker)

  10. 2. Theremin (Ætherphone) Physics • capacitance • ac circuits (RLC circuit resonance) • frequency mixing (heterodyne principle) Materials • Theremin • www.musiciansfriend.com • Moog (already built ) $389-$499 • Moog (kit) $339 • amplifier, speaker, audio cables • Moog 15-watt amplifier/speaker ($99)

  11. Theremin Patented in 1928 by Lev SergeyevichTermen (a.k.a. Leon Theremin in America) • played without physical contact • hand and antenna act as plates of a capacitor • distance between hand and antenna determines capacitance frequency “antenna” volume “antenna” http://www.thereminworld.com http://en.wikipedia.org/wiki/Theremin

  12. Pitch Control • uses 2 oscillators • one has fixed frequency • other frequency determined by capacitance of antenna-hand distance • difference of these two frequencies is audible frequency (heterodyne) Why use 2 oscillators and heterodyne? Why not just 1 oscillator? Capacitance is on order of picofarads so resonant frequency is in radio spectrum. Must mix two radio frequencies to get audible frequency. Volume Control • capacitance detunes oscillator which then attenuates signal

  13. Interesting Trivia http://en.wikipedia.org/wiki/Theremin The theremin was used in movie soundtracks such as Miklós Rózsa's for Spellbound and The Lost Weekend and Bernard Herrmann's for The Day the Earth Stood Still, and as the theme tune for the TV show Midsomer Murders. http://www.northwestchicagofilmsociety.org/ http://www.youtube.com/watch?v=3ULhiVqeF5U

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