# Dr. John Varriano Dr. Ted Clarke Jonathan Fili Department of Physics Christian Brothers University Electricity & Magnetism: Music to Our Ears TAAPT Annual.

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Dr. John Varriano Dr. Ted Clarke Jonathan Fili Department of Physics Christian Brothers University Electricity & Magnetism: Music to Our Ears TAAPT Annual Meeting March 21, 2015 Austin-Peay State University Clarksville, TN

1. Electric “Guitar”  electromagnetic induction  ac circuits  standing waves  musical scale Physics  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 Materials

Coil relays resistance  200-400  Example: NTE ELECTRONICS R46-5D12-12 POWER RELAY SPDT, PC BOARD Coil Voltage 12VDC Contact Voltage 120VAC Contact current 12A www.newark.comwww.newark.com \$3.89

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

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

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

12-tone equal temperament f 12 = 2f 0 f0f0 f1f1 f2f2 octave (1) bridge nut L0L0 LmLm dmdm (2) (3) Combining (1), (2), (3) gives Fret Bars?

Coil Voltage Output (before amplification)

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

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

Theremin http://en.wikipedia.org/wiki/Theremin frequency “antenna” volume “antenna” Patented in 1928 by Lev Sergeyevich Termen (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 http://www.thereminworld.com

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

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://en.wikipedia.org/wiki/Theremin Interesting Trivia http://www.northwestchicagofilmsociety.org/ http://www.youtube.com/watch?v=3ULhiVqeF5U

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