Introduction to session on absorbing and damping materials

Abstract

This paper provides an introductory framework to a session dealing with absorbing and damping materials. The opening segment describes analogs and differences between the two material concepts. Each in its respective sphere represents the principal engineering means of adding energy dissipation to control reverberation in a system. Some historical perspectives are noted, including conceptual simplicity and practical difficulties of use. Next is a brief review of major physical principles which influence performance. The analog of the role of treatment thickness on absorption and extensional damping performance is explored. The relation between normal and random incidence absorption and extensional damping performance is explored. The relation between normal and random incidence absorption coefficient is discussed. The recent work of Bliss [J. Acoust. Soc. Am. 71, 533–545 (1982)] on introducing an alternative boundary condition is explored for its relevance to this problem. An analog to coupled‐room acoustics problems exist in connected structures with applied damping. Maidanik's [J. Sound Vib. 77, 245–250 (1981)] recent work in this area will be discussed for its relevance to the performance of damping treatments. The third portion of the paper reviews recent properties measurements activities including ASTM C‐384, C‐423, and E‐756 as well as new measurement procedures. Closing remarks will deal with present and future directions of materials development.