In this paper, a design technique is proposed to extend the response of handset microspeakers toward low frequencies. This technique aims at finding the optimal parameters of the vented-box configuration using a systematic design procedure based on vibration absorber theory, where the system is viewed as two coupled serial and parallel oscillators. The characteristic equation of the vented box system is derived form the vibration absorber theory. A simulation platform is established on the basis of an electro-mechano-acoustical (EMA) analogous circuit. Electrical impedance and on-axis sound pressure level (SPL) of the microspeaker are simulated by solving the loop equations of the analogous circuit. Based on the characteristic equation of the vented box system, a design chart is devised to determine the parameters such that the system delivers the maximal output at the low-frequency end. In addition, a constrained optimization procedure is also applied to best reconcile the acoustic output and the enclosure constraints. Experiments were conducted to justify the optimal design. The on-axis SPL of the vented box system has been improved with the optimal design.
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