Moving magnet loudspeaker system with electronic compensation

Abstract

In most cases, an increase in voice-coil temperature is the major cause of speaker failure. Several techniques have been developed to keep the voice coil at room temperature under high-power inputs. It is a known fact that a rise in temperature causes a rise in the total resistance of the voice coil, thus reducing the sensitivity. Many performance improvements have been implemented on sound quality and high power output. However, less importance has been placed on the end stage of the hi-fi, i.e. the loudspeaker. The main problem faced by high-power loudspeakers is that of power compression. A cost-effective moving magnet structure, where the coil is directly heat sinked, is the best economical solution to reduce power compression. An attempt is made to build such a moving magnet loudspeaker system with a stationary coil. The compensation for the increase in voice-coil resistance is provided by predicting the temperature of the voice coil in real time at different temperatures. A computer controlled meas uring method is developed to enable long-term measurements with constant input power. A very simple digital technique to provide the required negative output impedance to compensate for the increase in voice-coil resistance is also discussed.