A study of efficient speaklet driving mechanisms for use in a digital loudspeaker array based on PZT actuators

The concept of a Digital Loudspeaker Array (DLA) requires a driving signal for a speaklet (tiny loudspeaker) with a short rectangle pulse. The speaklet takes the form of a diaphragm, which vibrates freely and emits acoustic energy at its resonant frequency. This study gives a guideline for the design of PZT speaklets for assigning the required resonant frequency and maximizing the amplitude of the acoustic response. The speaklet consists of three layers; a diaphragm, an active PZT layer, and a bottom electrode. The device is simulated with Comsol Multiphysics. From the simulation, the first resonant frequency mainly depends on diaphragm diameter and thickness while the maximum displacement is related to thickness of the three layer structure. Additionally, this study verifies the concept of a multiple-level DLA that can produce an acoustic signal with a linear relationship between its amplitude and the driving pulse width. This result allows a more flexible design of DLA as the limitation of one bit of resolution per speaklet is removed, allowing designs with a reduced number of speaklets.