Patent ID: 6975734
Filing Date: 2005-12-13
Classification: H03G,H04R

Abstract:
1. An audio apparatus for use in a negative impedance drive of a loudspeaker having an internal impedance to perform a desired amplitude-frequency characteristic, comprising: an amplifier device that drives the loudspeaker with a driving voltage; a providing section, that provides a control voltage, having as an input a voltage level indicative of a driving current to the loudspeaker; and a feedback device having a variable feedback gain that performs a positive feedback of a signal corresponding to the driving voltage of the loudspeaker to a positive input terminal of the amplifier device thereby causing the amplifier device to generate a negative impedance effective to negate the internal impedance of the loudspeaker, the feedback device comprising a voltage-controlled amplifier having the variable feedback gain and receiving the signal corresponding to the driving voltage, the voltage-controlled amplifier being responsive to the control voltage from the providing section and the signal corresponding to the driving voltage for generating an output signal and positively feeding back the output signal to the positive input terminal of the amplifier device to thereby perform the positive feedback, wherein the providing section provides the control voltage that decreases the variable feedback gain as the voltage level indicative of the driving current to the loudspeaker increases, thereby adjusting the amplitude-frequency characteristic of the amplifier device, only if a level of a loudspeaker output exceeds a predetermined output level, and otherwise keeps the variable feedback gain constant as long as the level of the loudspeaker output remains under the predetermined output level.