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The development of mobile phones as multimedia devices has led to limited insertion space for microspeakers, particularly due to wider liquid crystal displays. To enhance the performance of microspeakers in a limited area, this paper proposes a technique for designing a magnetic circuit considering the effective area of the diaphragm. The comparison between magnetic flux density and magnetic forces between conventional and the proposed magnetic circuit was carried out using finite element analysis. For higher flux density, alteration of the magnetic circuit was performed. Because every microspeaker is structurally sealed in a small back volume, expect for the top sound emission side, this work considered using a small back volume under the diaphragm. Although the flux density of the proposed microspeaker is higher than that of the conventional type due to alteration of the magnetic circuit, the magnetic force is less than that of the conventional type due to the effect of the voice coil. However, because of the small effective area of the diaphragm and the lightweight voice coil, the sound pressure level (SPL) of the proposed microspeaker is higher than that of the conventional type. The SPL obtained by a mathematical approach is compared to the experimental results.