Analysis of harmonic distortion due to uneven magnetic field in a microspeaker used for mobile phones

With the advent of 2.5-G mobile phone, Internet service is to be realized for multimedia data communication. For an acoustic part, a smaller and lighter microspeaker is also soon to be realized as an MP3 song player and a speakerphone. Harmonic distortion due to uneven magnetic field in the microspeaker is becoming more important in mobile phones in order to generate high-quality sound. In this paper, analysis of sound pressure level and harmonic distortion is presented by considering mechanical and magnetic coupling effects. Experimental verification is also followed for inner and outer permanent magnet (PM)-type microspeakers. Results show that the outer PM-type microspeaker shows better sound pressure characteristics with reduced harmonic distortion.