File:Early permanent magnet speaker 1933.jpg
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| Description |
English: A Magnavox permanent magnet loudspeaker from a 1933 advertisement in an electronics magazine. This was just before the development of alnico magnets (which started in 1931) and previous speakers required electromagnets to create strong enough fields for adequate volume. Stronger magnetic alloys allowed this speaker to use a permanent magnet, but requires a long horseshoe shape to produce the required field. The development of alnico in World War 2 allowed a magnet only an inch long to produce the same field, and led to a new generation of compact loudspeakers in the postwar era. |
| Date | |
| Source | Retrieved October 23, 2014 from Electronics magazine, McGraw-Hill Publishing Co., New York, Vol. 6, No. 11, November 1933, p. 1 on American Radio History website |
| Author | Unknown author |
| Permission (Reusing this file) |
This image is from an advertisement for the Magnavox Corp. without a copyright notice published in a 1933 magazine. In the United States, advertisements published in collective works (magazines and newspapers) are not covered by the copyright notice for the entire collective work. (See U.S. Copyright Office Circular 3, "Copyright Notice", page 3, "Contributions to Collective Works".) Since the advertisement was published before 1978 without a copyright notice, it falls into the public domain. |
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This work is in the public domain in the United States because it was published in the United States between 1929 and 1977, inclusive, without a copyright notice. For further explanation, see Commons:Hirtle chart as well as a detailed definition of "publication" for public art.
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| Date/Time | Thumbnail | Dimensions | User | Comment | |
|---|---|---|---|---|---|
| current | 01:26, 25 December 2014 | | 386 × 383 (30 KB) | Chetvorno (talk | contribs) | User created page with UploadWizard |
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