Abstract
Measurements of the sound absorbed by small samples of material one foot square were obtained for five pitches,—4096, 2048, 1024, 512, 256, with numerical calculations of coefficients for the three higher pitches. Diffraction effects at the pitches 512 and 256 made the calculations uncertain. Sound from an electrodynamic loudspeaker passed through a cast iron tube 8 inches in diameter and 2 feet long where it impinged on the material placed at an angle of 45° to the axis of the tube. It was thus reflected so as to pass at right angles to its original direction through a side opening in the tube to a condenser microphone where it was measured. The path from the material to the microphone was enclosed by a tube of ground cork 2 inches thick held in place by porous metal screening. Additional measurements were taken with the sample removed (theoretically, 100 percent transmission, 0 percent reflection) and also with a thick glass plate replacing the material (100 percent reflection). Further experiments are in progress to get coefficients at the lower pitches.
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