11.1. Introduction

The role of an electro-acoustic system is to convert a signal in a given form (electric, acoustic, optic, magnetic, piezoelectric, magnetostrictive, etc.) into a usable signal in another form (from among the same list). For example, a classic loudspeaker converts an electric signal into an acoustic signal while a classic microphone does the inverse conversion. This conversion is, most of the time, not straightforward: in the previously cited cases, a mechanical system is at the interface between the "electrical" domain and the "acoustical" domain. An electro-acoustic system provides a "cascade" of strong couplings between successive "media" of different natures. The object of this chapter is to present some general models to deal with the typical problems related to these strongly-coupled frameworks.

This chapter, by making use of previously introduced notions, does not present new concepts, but illustrates the importance of "strong coupling", an unavoidable notion in acoustics, and provides the reader with simple and commonly used methods to describe these phenomena.

For the sake of simplicity, the important classes of electro-acoustic systems are presented separately. The different types of conversion are presented in the first section, the linear mechanical systems with localized constants are dealt with in the third section and, finally, the acoustical systems are given in the fourth section. A few practical examples that illustrate the various types of conversion are given in the fifth and last section. Finally, fundamental notions on linear electric circuits with localized and distributed constants are set out in the Appendix...