水中吸音材の複素音響諸定数の測定

抄録

The author a devised method for computing complex acoustic contants of absorbers in water from values of acoustic impedances of the samples which were measured by the set up for measuring complex pressure reflection coefficients. In this method, acoustic constants are computed from measureed values of the acoustic impedance of two samples different in thickness under a condition that back surfaces of samples are kept free, as it is difficult to keep those surfaces rigid in water. This method is capable of being employed even for measuring the constants of samples whose absorption coefficients are zero or very large. Acoustic constants of wood (pine) containing water up to saturation and some trial products of rubbers containning aluminum powder and rubbers containing lead powder as absorbers, were measured at 9〜36kc, and it was found that very likely the absorption coeffisients had close relation to the elasticities. Also, sound velocities in samples of natural rubbers, neoprenes and polyester resins(non-absorbent materials)were measured by this meihod. Differences between measured values by this method at 27kc and those by other methods in higher frquency range, were less than about several percents.