Nonlinear parameters identification of moving coil miniature loudspeakers

Abstract

Due to its physical design, moving coil loudspeakers exhibit distortion at high excursion signals. The identification of the nonlinear parameters gives the physical cause of the distortion, which is important for diagnostics and allows for a more realistic modeling. This work presents a measurement system for nonlinear parameters of miniature moving coil loudspeakers by using voltage, current and laser displacement sensors. The voice coil electrical resistance (R E ) and the mechanical mass (M MS ) are defined as linear parameters. As nonlinear parameters, the force factor (Bl), the stiffness (K MS ) and the voice coil inductance (L E ) are defined as a function of the instantaneous voice coil displacement. In addition, for microspeakers characterization, the mechanical resistance (R MS ) is defined as a function of the voice coil velocity. In order to identify the parameters, the driver under test is excited by a large amplitude signal meanwhile the voltage, the current and the voice coil displacement are acquired. The measured signals are then fitted in time domain by using nonlinear least-squares identification technique to the ones numerically obtained from the modeled loudspeaker. Measurement results demonstrate the reliability of the measurement system.