Measurements and analyses have also been made of the sound fields inside parabolic reflectors. A parabolic reflector is used to collect and focus sound waves to a microphone receiver 1. This directivity theory has been applied to existing published directivity curves and data of Schneider, Obata and Yosida. A parabolic dish microphone is like a mirror telescope for sound. Recent measurements are described giving additional checks on the amplification theory of Rocard and Gutin, and verification of Gutin's formulas for directivity. 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. Used mainly for outdoors recording of birds, sports and spying. The waveguide radius (a) was 0.5 mm, the focal length of the 1 st parabolic reflector n and the 2 nd parabolic reflector m equaled to 10 and 0.5 mm. 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. It is a microphone with a dish to concentrate sound waves and pick them up. The shape of the illumination (buzzword: 'tapering') itself determines the size and number of sidelobes that may. Depending on the illuminator (source) the factor ' 70 70 ' may vary between 60 60 and 100 100, or so. The two parabolic, nickeled reflectors are 54cm in diam., they are adjustably mounted on cast-iron tripod supports. The first theoretical treatment of amplification was made by Rocard in the Revue d'acoustique in 1932. The beamwidth of a parabolic dish is on the order of BW 70 D B W 70 D measured in degrees. ![]() 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. In practice, though a parabolic shape will produce the best sound quality, almost any dish like reflector will work. Some experiments have been carried out with a parabolic bowl to test the more recent theoretical analyses never before verified. ![]() ![]() A compendium of all published experimental and theoretical work on parabolic reflector‐type sound concentrators has been made.
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