TABLE OF CONTENTS When airborne sound from the human voice is transmitted from one room to another, the resulting vibration on the walls and floors in the receiving room is at a sufficiently low level that it can rarely be perceived with our fingertips. Ears are rather more sensitive, so if the background noise level in the receiving room is low, and the airborne sound insulation is quite low too, we can detect the sound pressure radiated by these vibrating walls and floors. This chapter looks at the theory describing vibration fields and relates it to plates and beams that are used to build walls and floors in buildings. An understanding of vibration fields, power input into structures, and sound radiation from vibrating structures is essential to the study of sound insulation. Compared to sound fields the degree of complexity increases due to the existence of different wave types as well as a wide range of wavelengths over the building acoustics frequency range.
The main structural building components for which we need to describe the vibration fields are beams and plates (see Fig. 2.1). Rooms are bounded by plates in the form of walls and floors; hence plates play the key role in both sound radiation and structure-borne sound transmission. Many walls and floors, or their constituent parts, can be represented as solid plates hence these form a fundamental building element. In practice there are many plates with more complicated forms, such as walls built from masonry blocks with large internal...
