New geometric sound absorbers

Abstract

In a previous paper of the same name, two new geometric sound absorbers were discussed. The geometric absorbers use closely coupled quarter‐wave resonators to absorb sound. Because the structures absorb sound by their configuration, they do not require the use of conventional porous or fibrous sound‐absorbing materials and can be made of nearly any substance such as plastic, wood, metal, etc. The absorbers can be made very rugged and long‐lasting for industrial, military, and outdoor use. The previous paper discussed two basic sound absorbers, configuration delta and flat absorber, but the paper concentrated on the former sound‐absorber configuration. This paper will review configuration delta but will concentrate on describing the structure and performance of the flat absorber. This absorber can be made in a thin treament, less than 25 mm thick, that provides high acoustic absorption. A number of different designs will be shown, and the results of standing wave tube and reverberation room tests will be given. Combining the two treatments described in this paper provides a broad frequency range absorber that is both compact and rugged. Helmholtz resonators can also be used with the flat absorber concept, and this is discussed.