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Summary form only given. With the advent of 2.5G mobile phone, internet service is to be realized for multimedia data communication. For acoustic parts, a smaller and lighter micro-speaker is also soon to be realized as a MP-3 song player and speakerphone. With uneven magnetic field due to reduced magnetic circuits, harmonic distortion is induced to degrade sound quality. Using FEM, this article shows magnetic flux line of the micro-speaker and uneven exciting force can be predicted as the voice coil vibrates. With mechanical analysis using FEM, surface velocity of the vibrating diaphragm can be determined. The sound pressure level can be also determined using acoustical analysis by assuming diaphragm as a monopole source. For high quality sound generation, harmonic distortion should be minimized by appropriated magnetic circuit design.