Fig. 1: Schematic (.-1) & equivalent circuits (.-2) of loudspeaker and piezoelectric diaphragm.
a In-tube electrodynamic loudspeaker. When an input current i(t) flows through the transducer voice coil, a Lorentz force is generated, forcing the diaphragm to move with a velocity \(v=\dot{\xi }(t)\). The loudspeaker can be modeled by an equivalent electromechanical circuit a-2 that involves the mass Mms, the resistance Rms, and the compliance Cms of the membrane/diaphragm, as well as the electric resistance Re and inductance Le. b closed-box loudspeaker. When the loudspeaker is embedded within a closed box/cabinet of volume Vb, it reacts with added mechanical compliance \({C}_{me}={V}_{b}/({S}_{d}^{2}\rho {c}^{2})\). c Piezoelectric diaphragm. Under external voltage, the piezoelectric diaphragm reacts with a change in its volume ΔV characterized by Q, the volumetric change rate. As a result, a pressure drop across the diaphragm is generated. The equivalent circuit is composed of the blocked capacitance of the piezo-diaphragm CPB, and the mechanical compliance CD and mass MD of the diaphragm, linked through the electro-acoustic transduction coefficient ψ.
