Abstract: An electro-acoustic system including an amplifier circuitry for amplifying an input signal to provide an amplified signal; and electrodynamic loudspeaker having at least one magnet, a diaphragm connected to a coil support, a voice coil for driving a diaphragm in response to the amplified signal with the presence of the magnet, and an electromagnetic impedance sensor coil partically offset with the at least one magnet for providing a feedback signal proportional to its electromagnetic impedance which is a function of both the moving speed and the displacement of the diaphragm; a negative feedback circuitry processing the feedback signal and providing a negative feedback signal; and a summing circuitry for combining the input signal and the negative feedback signal and sending a combined signal to the amplifier circuitry, which in turn provides an amplified combined signal to the electrodynamic loudspeaker to thereby reduce the distortion of the electrodynamic loudspeaker.

Abstract: An improved working point adjusting circuit for a single power amplifier having multiple output circuits. When this simple circuit is connected to a Class B transistor power amplifier to support two or more output channels or speakers, it adjusts the working point of the transistors in the output circuit of the power amplifier to the linear portion of the current-voltage characteristics of the transistor so the amplifier works in the level of a Class A amplifier. It provides many significant advantages including (1) much higher energy efficiency on output transistors; (2) much less signal distortion on loaded speakers; (3) simple circuitry for increased reliability; (4) low component count for reduced costs; and (5) individualized adjustment for each output channels which eliminates the different effect caused by the very fine differences between the multiple loaded output devices such as loudspeakers.