File:Ribbon microphone cover off.jpg

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Summary

DescriptionRibbon microphone cover off.jpg	English: RCA ribbon microphone from 1932 with cover removed, showing construction. The magnet is visible at center, while the narrow duralumin ribbon is suspended between the triangular pole pieces (top). The vibration of the ribbon back and forth in the horizontal magnetic field induces vertical alternating currents in the ribbon by electromagnetic induction which are picked off by wires attached to the top and bottom. It was called a "velocity" microphone because the signal produced is proportional to the velocity of the ribbon and thus the air molecules, in contrast to other microphones in which the output is proportional to the displacement of the diaphragm. Caption: The RCA Victor "velocity" microphone with the cover removed to show the thin strip of metallic ribbon suspended between the pole pieces of the permanent magnet. Other microphones use diaphragms which tend to over or under emphasize certain tones which resonate with the mechanism. The vibrating mechanism of the new "velocity" microphone is actuated by the velocity of the minute air particles set in motion by the sound waves. Alterations to image: rotated 90° to show it in natural orientation in which it is used.
Date	September 1932
Source	Retrieved April 9, 2014 from Radio Engineering magazine, Bryan Davis Publishing Co., New York, Vol. 12, No. 9, September 1932, p. 15 on American Radio History website
Author	Unknown authorUnknown author
Permission (Reusing this file)	This 1932 issue of Radio Engineering magazine would have the copyright renewed in 1960. Online page scans of the Catalog of Copyright Entries, published by the US Copyright Office can be found here. [1] Search of the Renewals for Periodicals for 1959, 1960 and 1961 show no renewal entries for Radio Engineering. Therefore the magazine's copyright was not renewed and it is in the public domain.

Licensing

This work is in the public domain because it was published in the United States between 1929 and 1963, and although there may or may not have been a copyright notice, the copyright was not renewed. For further explanation, see Commons:Hirtle chart and the copyright renewal logs.
Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (70 years p.m.a.), Mainland China (50 years p.m.a., not Hong Kong or Macao), Germany (70 years p.m.a.), Mexico (100 years p.m.a.), Switzerland (70 years p.m.a.), and other countries with individual treaties.

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