ABSTRACT
This chapter uses impedance and intensity commonly both in sound radiation from vibrating structures and in sound propagation. It discusses the various types of impedance followed by a discussion of both sound intensity for sound propagation in a gas and structural intensity for sound waves propagating in structures. The chapter observes a number of similarities and differences for the two different types of intensity. Fundamentally, sound and structural intensity are both a measure of the energy that is propagating in the respective medium. The chapter discusses that impedances are generally associated with acoustic sources or acoustic propagation. The radiation impedance of a surface or acoustic source is a measure of the reaction of the acoustic medium against the motion of the surface or source. It is really a special case of a mechanical impedance applied to a source of sound.
