Novel Design of Dual Voice Coil Microspeaker with Reduced Back Volume

Microspeakers are typically used in portable devices to generate sound. As smartphones become increasingly compact, the space available for microspeakers also decrease, which reduces the back volume from $0.60\ \text{cm}^{3}$ to $0.25\ \text{cm}^{3}$. This reduction results in an increase in the stiffness of the microspeaker, which affects the sound pressure level (SPL) at low frequencies. This paper proposes a dual-coil microspeaker design for SPL enhancement at low frequencies while maintaining the same size as a prototype microspeaker. The analysis method uses to solve the electromagnetic-mechanical-acoustic coupling system is verified experimentally in advance. The proposed dual-coil microspeaker is designed and analyzed using three-dimensional finite element methods. Samples are manufactured and measured. Compared to the prototype, the novel dual-coil microspeaker in serial connection presents a higher Lorentz force (+7.4 %), resulting in an SPL improvement of 2.27 dB at low frequencies.