Effect of nonlinear stiffness on the total harmonic distortion and sound pressure level of a circular miniature loudspeaker-experiments and simulations

This paper reports our study on the nonlinear stiffness of a few diaphragm designs used for miniature loudspeakers. For this study, the sample diaphragms were experimented for their stiffness curves using the laser vibrometry. Additionally, the stiffness curves were also obtained using finite element analysis (FEA). For calculating total harmonic distortion (THD), the electroacoustic system is modeled using the equivalentcircuit analogy. As a result of solving the coupled system of ordinary differential equations by the Runge-Kutta method, THD of three sample designs, characterized by different track patterns, were calculated and plotted as a function of frequency. The specimens were tested in a standard anechoic chamber for recording THD. Additionally, the sound pressure level (SPL) curves of these specimens were also recorded for comparison. It turns out that, despite no significant SPL difference, diaphragms with different track patterns shall, as a result, lead to substantial variations of THD. The consistence of our simulations with the measured THD has promised the feasibility of simulating THD by FEA for optimizing the design of track patterns for diaphragm.