In this experimental investigation, the acoustic absorption characteristics of various species of wood, rubber, and wood/rubber composites were determined under low hydrostatic pressure and over the frequency range 10–50 kHz. The test samples, including white pine, douglas fir, redwood, fir plywood, Saper-Trubber, and bubble rubber were typically 4 ft sq and tested in a 948-gal semianechoic water tank. A tone-burst technique was used to minimize extraneous signals resulting from wall and surface reflections. The standing wave pattern was measured in front of each sample at discrete frequencies. From the standing wave pattern, and from the classical theory of waveguide propagation, the complex reflection factor, material longitudinal phase velocity, and attenuation per unit depth were determined as a function of frequency. It was found that the absorption characteristics of all woods improved as the moisture content increased to the saturation point. Redwood exhibited the best characteristics and this was improved by approximately 50% when backed by a 1/4-in. layer of Saper-T sound absorbing rubber. Fir plywood did not have the lowest reflection factor, but did exhibit the smoothest frequency response of the woods evaluated.