To create the complete circuit, in addition to the two current controlled voltage sources (HX), the voltage controlled voltage source (EX) and the current controlled current source (FX), two constant voltage sources (VX) are also required; the latter, if set to zero, in SPICE, are used as ammeters.
To understand how electro-mechanical transduction takes place, let’s look at the equivalent electrical diagram of the entire system, divided into its three components, in Figure 9. The voltage (force) source H2 is controlled by the current, detected by V2, flowing in the voice coil of the loudspeaker. In the same way the current (speed) flowing in the mechanical circuit, detected by V3, controls the voltage source H1, giving rise to the back EMF (counter-electromotive force) in the voice coil. Since e=(Bl)u and f=(Bl)i, the gain of both controlled sources corresponds to the driver’s Bl parameter.