Design and Analysis of Microspeakers to Improve Sound Characteristics in a Low Frequency Range

The performance of a microspeaker was evaluated according to its sound pressure level (SPL). Generally, it is desirable for a microspeaker to have a constant and high SPL that covers the whole audio frequency range. A microspeaker has a relatively high and even SPL for frequencies higher than the first resonance frequency, but its performance is subpar for frequencies below that first resonance frequency. Many sound sources, including people´s voices, have low frequency ranges; therefore, it is critical to improve the low-range performances of the microspeaker. This paper presents a method to improve the low-range SPL by improving the magnetic circuit structure and changing the diaphragm shape. To improve the electromagnetic force, the existing two-magnet circuit structure was changed to a one-magnet circuit structure, and the magnet volume was maximized in the process. Accordingly, the wire diameter was expanded and more coils can now be used at the same resistance. Therefore, despite the increase in the air gap, the electromagnetic force improved. In addition, the shape and material of the diaphragm were changed, and the vibration system mass was increased. Due to these changes, the first resonance frequency decreased and the low-range characteristics improved. This study analyzed this new microspeaker design through electromagnetic, mechanical and acoustic coupling relations, in addition to conducting verification through pilot product manufacture and experiments.