ABSTRACT
A prominent acoustical consultant once said, "All materials are acoustical materials, but some are better than others." This chapter considers the various types of acoustical materials, their acoustical properties, and those parameters used to describe these properties. Acoustical materials can be divided into three basic categories such as absorbing materials, barrier materials, and damping materials. Absorbing materials are generally resistive in nature, either fibrous, porous, or, in rather special cases, reactive resonators. Classic examples of resistive material are fibrous glass, mineral wools, felt, and polyurethane-type foams. Resonators include hollow core masonry blocks, sintered metal, etc. Effective barrier materials have one basic common property: dense mass. The most effective barrier materials also have a high degree of internal damping which qualitatively is described as limpness. Damping materials are usually relatively thin coatings of plastic polymers, metal, epoxy, or glue which can be adhered to sheet metal panels, gears, machine parts, etc.
