Numerical and experimental analysis of harmonic distortion in a moving-coil loudspeaker

The nonlinear effect of a moving-coil loudspeaker, originating from its magnetic coupling factor and the system’s stiffness, presents a significant impact on the sound quality. For improving the sound quality, this article proposes an approach to reduce the total harmonic distortion (THD) by adjusting the initial position of its voice-coil. First, a mathematical model involving the nonlinearities of force factor, mechanical stiffness, and inductance of voice coil is constructed and then solved using a novel algorithm called the parameter spline difference method (PSD). In the course of pursuing reduction of the corresponding THD of a typical moving-coil loudspeaker, the model was used to analyze the nonlinearity of the THD, revealing itself as a nonlinear function of force factor, the system’s stiffness and inductance of voice coil. For various initial positions of the voice-coil, the coupled nonlinear differential equations were solved using the PSD to yield corresponding sound pressure level and THD. To our satisfaction, the loudspeaker driver with its voice-coil optimally tuned for the initial position turns out to have a THD reduction of 10%, which is also consistent with our experimental observations.

► Establishes a mathematical model and coupled ordinary nonlinear differential equations for a moving-coil loudspeaker.
► Applies a novel algorithm called the parameter spline difference method to solve coupled nonlinear differential equations.
► Proposes an approach to reduce the total harmonic distortion (THD) by adjusting the initial position of its voice-coil.
► Demonstrates that the proposed approach is an expedient, yet reliable, tool to predict the THD of a moving-coil loudspeaker.