Abstract
This study is to develop miniaturizing loudspeakers for handheld devices, where the thinness, volume and efficiency of the loudspeaker are the major concerns. Polyvinylidene fluoride (PVDF) loudspeaker is one of the candidates for its properties of thin and efficiency. The membrane of PVDF loudspeaker is slightly curved in order to convert in-plane strains into transverse ones. To facilitate the design optimization, a simulation platform is established with a hybrid analogous circuit. While the circuit is primarily a lumped parameter in nature, the mechanical impedance can be derived from a finite-element analysis. The mechanical impedance, along with a more precise model of radiation impedance, enables the prediction of the high order modes of the loudspeaker. The simulation results indicate that a reduced radius of curvature leads to an increased sound pressure level and a higher resonance frequency. To identify the lumped parameters, a series of special procedures is developed. Based on the measurement of electrical impedance, the electrical capacitance is estimated. The mechanical parameters and the coupling factor are identified through the measurement of diaphragm velocity with a laser vibrometer. To optimize the design parameters of the loudspeaker, the simulated annealing (SA) algorithm is used under practical constraints. The results have shown that, with the optimal configuration, the sound pressure level increases by 15 dB and the resonance III frequency increases by 700 Hz, as compared with a non-optimal design. Although the PVDF loudspeaker is thin and efficient, the area it required is too large for handheld devices. BA speaker take the advantages of tiny size and stronger electro-mechanical coupling coefficient, let it be a choice of high potential. After deriving the electro-mechanical coupling coefficient of BA speaker, the EMA model of BA speaker is found that it is identical to the one of moving-coil speaker. The ID procedure and optimal method used before can apply to it as moving-coil loudspeaker. A platform of optimal design for BA speaker is established.