The theory of electrical circuits has been applied to the study of electromechanical vibrating systems since the early 1900s, but its use for the design of loudspeaker systems was first described in 1952 by Bart N. Locanthi [9]. The great diffusion of this method occurred shortly afterwards, probably after the publication in 1954 of Acoustics [13] by Leo Beranek, considered the reference text on acoustics still today. Beranek described in detail the two types of analogies (mobility and impedance) that allow the use of resistors, inductors and capacitors as basic mechanical or acoustic elements and illustrated the transformers technique (and their transformation ratios) to couple the electrical, mechanical and acoustic section of the loudspeaker into a single equivalent electrical circuit from which the transfer function of the entire system can be derived. This approach was also used by Thiele and Small to identify and describe the fundamental parameters of the loudspeakers (which still bear their name) and to analyse the behaviour of closed and bass-reflex enclosures.

At a practical level the transformer technique obliges the designer to use the mobility analogy, however, when it comes to modelling an acoustic device, it is preferable to use the impedance analogy, where the sound pressure is the equivalent of the electric voltage in the analogous circuit: to measure the sound pressure in an acoustic circuit it is sufficient to place a microphone probe in the desired point without making any modification to the system; similarly we can easily measure the voltage in a point of the electric circuit by applying a probe without modifying or interrupting it. If we decided to use this model of analogy, particularly suitable for acoustic circuits, applying the transformer technique, since we could not use two different types of analogy in the same system at the same time, we would be obliged to apply it to the whole equivalent circuit and a big difficulty would arise in coupling the mechanical part of the loudspeaker with its electrical part: the mechanical force moving the loudspeaker (the voltage in the equivalent circuit, using the impedance analogy) comes from the current flowing in its electric circuit (f=Bli, where Bl, a parameter usually supplied by the loudspeaker manufacturer, represents the motor force factor). In order to obtain the correct conversion from current to voltage we would then be forced to apply the principle of duality of the electric circuits to the electric section of the driver, complicating the model considerably (especially if we wanted to include a crossover filter in the simulation).

In 1991 W. Marshall Leach, Jr. [14] described the use of the circuit simulation program SPICE applied to the design of electroacoustic systems. The main advantage introduced by the use of SPICE is the possibility to use controlled-sources, instead of transformers, for the coupling of the three sections of the electro-mechanical-acoustic system. The controlled sources allow the use of impedance analogy without upsets in the electrical section of the system. Potentially, it would also be possible to use both types of analogy simultaneously, however, as the problem is essentially an acoustic one, it is convenient for practical purposes to use only the impedance analogy.

The powerful graphical interface of SPICE also allows a quick analysis of the main features of the system such as frequency response, impedance curve and speaker cone excursion.

In his paper Leach provided the equivalent circuits for various types of acoustic transducers, microphones and closed and reflex speaker systems, taking into account for the latter also the mutual coupling between woofer and duct.