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ABSTRACTS
Moving-Coil Telephone Receivers and Microphones. E. C. WENTE AND A. L. THURAS. /. Acoustical Soc., Ill, No. 1, Part 1, July, 1931, p. 44. This paper is concerned primarily with the general principles of design of moving-coil receivers and microphones. There are included circuit diagrams for several systems together with the calculated and experimentally measured response curves of a moving-coil head receiver and a moving-coil transmitter.
In regard to the microphone it "has important practical advantages over the condenser transmitter in that the amplifier may be at some distance from the transmitter without loss in efficiency and in that no polarizing voltage is required. The sensitivity of this transmitter is about 10 db. higher." W. A. M.
Mass Controlled Electrodynamic Microphones. H. F. OLSON. /. Acoustical Soc., m, No. 1, Part 1, July, 1931, p. 56. A theoretical discussion of a mass controlled electrodynamic microphone is presented. A microphone of this type, which consists of a light corrugated ribbon suspended in a magnetic field and freely accessible to air vibrations, is described . The theoretical response-frequency characteristic to be expected is calculated and compared with the measured characteristic. The response is shown to be substantially uniform between 100 and 5000 cycles. A more detailed account of the application of the ribbon microphone will be found in an article by H. F. Olson, J. Soc. Mot. Pic. Eng., June, 1931. W. A. M.
Microphone Technic in Radio Broadcasting. O. B. HANSON. /. Acoustical Soc., HI, No. 1, Part 1, July, 1931, p. 81. This paper is especially concerned with the difficult task of picking up action which takes place over a large area, such as symphony orchestra and stage presentation of an opera under conditions where the arrangement of the players cannot be adjusted to be ideal for sound pick-up. In particular is the use of a parabolic reflector discussed. Several specific cases of the usefulness of such a directional pick-up device in actual broadcasting are described. Also response curves of the directional effect at various frequencies are shown The author believes that the development of a directional pick-up has been a great step forward in microphone technic and he expects to see considerable development in directional microphones in the next few years, which in turn will enable broadcasters to build larger productions and transmit them with even more fidelity than at present. W. A. M.
The Development of the Microphone. H. A. FREDERICK. /. Acoustical Soc., Ill, No. 1, Part 2, July, 1931. This paper is a presentation of the history of the microphone starting with developments as far back as 1837 and carried through to the present time. During the period immediately following 1875, almost every conceivable type of microphone was tried. Since the magnitude of the electrical output was of more importance than extreme faithfulness of reproduction, the granular carbon type of microphone rapidly came to the front, and extensive work on this type of transmitter led to successive improvement of both these 860