Improvement Of Loudspeaker Performance Through The Use Of Feedback

Abstract

This paper compares two methods of measuring the motion of a loudspeaker cone. An accelerometer device was built by designing and attaching a preamplifier to the piezoelectric crystal transducer assembly. This crystal has a voltage output proportional to the acceleration of the loudspeaker cone. The other technique consisted of measuring the back emf across the voice coil by using a bridge network. The voltage obtained is proportional to the velocity of the loudspeaker cone. Measurements indicate that for a sinusoidal input the velocity and acceleration voltages have a 90° phase shift. Thus, both methods of measurement are in agreement with theory. Feedback will also reduce the harmonic distortion caused by a nonlinear suspension system. Also, a mathematical analysis is made to determine tile effects of acceleration, velocity, and displacement feedback on the frequency of the system.