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SUPERCONDUCTING VOICE COIL – A ROUTE TO INCREASE EFFICIENCY OF AN ELECTRODYNAMIC LOUDSPEAKER

SUPERCONDUCTING VOICE COIL – A ROUTE TO INCREASE EFFICIENCY OF AN ELECTRODYNAMIC LOUDSPEAKER. Ivan Djurek *1 , Danijel Djurek *2 , Branko Somek *1 *1 Faculty of EE and Computing, Zagreb, Croatia *2 AVAC, Zagreb, Croatia. INTRODUCTION. Complex system Several steps of energy transformation

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SUPERCONDUCTING VOICE COIL – A ROUTE TO INCREASE EFFICIENCY OF AN ELECTRODYNAMIC LOUDSPEAKER

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  1. SUPERCONDUCTING VOICE COIL – A ROUTE TO INCREASE EFFICIENCY OF AN ELECTRODYNAMIC LOUDSPEAKER Ivan Djurek*1, Danijel Djurek *2, Branko Somek *1 *1Faculty of EE and Computing, Zagreb, Croatia *2AVAC, Zagreb, Croatia

  2. INTRODUCTION • Complex system • Several steps of energy transformation • Loss of energy • Hard to construct the loudspeaker with low distortion level and high efficiency • Possible route: SC voice coil

  3. CONVENTIONAL LOUDSPEAKER • Example of forced damped oscillator • M – mass of voice coil and membrane • RS, XS – real and imaginary part of emission impedance • k – elastic restoring force • RM – friction part

  4. CONVENTIONAL LOUDSPEAKER • Emission impedance • Imaginary part represented with aproximation of Struve function [3]

  5. CONVENTIONAL LOUDSPEAKER • Characteristics of used commercial loudspeaker Manufacturer data

  6. CONVENTIONAL LOUDSPEAKER • Current from back electromotive force (BEF) • Driving force • Amplitude of oscillation

  7. CONVENTIONAL LOUDSPEAKER • Amplitude at resonant frequency

  8. CONVENTIONAL LOUDSPEAKER • Total power • Efficiency

  9. CONVENTIONAL LOUDSPEAKER • Efficiency of used commercial loudspeaker

  10. LOUDSPEAKER WITH SC VOICE COIL • Changes: • One turn in voice coil: l = 0.075 m • RC = 0 W • No inductance - L • Total mass (calculated): 11 g

  11. LOUDSPEAKER WITH SC VOICE COIL • Efficiency

  12. EXPERIMENTAL • Test of previous calculations • Copper voice coil cooled to 130 K (-143°C) • Vibration amplitude vs resistance of voice coil

  13. EXPERIMENTAL • Amplitude and resistance measurements f=40 Hz

  14. DISCUSSION • Advantages: • Disappearance of electro-mechanical coupling terms > lower distortion • Reduction of voice coil inductance L • Reduction of mass • Higher efficiency • Problems: • Impedance matching between SC loudspeaker and common amplifiers • Cooling

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