Abstract

A compendium of all published experimental and theoretical work on parabolic reflector-type sound concentrators has been made. Some experiments have been carried out with a parabolic bowl to test the more recent theoretical analyses never before verified. The experimental data on amplification and directivity published in 1930 by Obata and Yosida of the Aeronautical Research Institute, Tokyo Imperial University, has been checked by the new theory. The first theoretical treatment of amplification was made by Rocard in the Revue d'acoustique in 1932. In 1935 the experimental verification of this expression for amplification was published in the Zhurnal Teknicheskoi Fiziki by Schneider, an engineer at the Moscow Radio Center. Also in 1935, Gutin, a physicist in Leningrad, derived independently the expression for amplification and went on to work out the theory of directivity which he published in the Izvestia Elektropromishlennosti Slabovo Toka. Recent measurements are described giving additional checks on the amplification theory of Rocard and Gutin, and verification of Gutin's formulas for directivity. This directivity theory has been applied to existing published directivity curves and data of Schneider, Obata and Yosida. Measurements and analyses have also been made of the sound fields inside parabolic reflectors.

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