File:Western electrics rundradiomikrofon i sitt skyddande fodral, Nordisk familjebok.png
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English: Early Western Electric Model 357 double-button carbon microphone in 1B housing, from early 1920s. The double-button was an improved carbon microphone design developed by Western Electric, the manufacturing arm of the Bell Telephone system (AT&T) around 1921 that was very widely used for the first AM radio broadcasting as well as for PA systems and recording throughout the 1920s. It is often seen in period photos in its "ring and spring" form with the housing removed, as a small microphone cylinder suspended in the center of a metal ring by springs. The springs (visible above through the holes) isolated the microphone from vibrations of its supports. The first carbon microphones had the carbon cell or "button" attached to one side of the diaphragm which picked up the sound. This caused harmonic distortion because the change in the carbon's resistance was nonlinear, different for inward (compression) and outward (tension) displacements. The double-button design had two carbon "buttons", one attached to each side of the diaphragm, connected in a "push-pull" circuit, which canceled even-order harmonic distortion. The stiff duralumin diaphragm had a very high resonant frequency and air damping, further reducing distortion and giving it a flat frequency response The cost for this higher fidelity was that it had very low output, however. |
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| Source | https://runeberg.org/nfcr/0059.html |
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From https://runeberg.org/nfcr/0059.html
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This image was first published in the 1st (1876–1899), 2nd (1904–1926) or 3rd (1923–1937) edition of Nordisk familjebok. The copyrights for that book have expired and this image is in the public domain, because images had no named authors and the book was published more than 70 years ago.
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This image (or other media file) is in the public domain because its copyright has expired and its author is anonymous.
This applies to the European Union and those countries with a copyright term of 70 years after the work was made available to the public and the author never disclosed their identity. Important: Always mention where the image comes from, as far as possible, and make sure the author never claimed authorship. |
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Note: In Germany and possibly other countries, certain anonymous works published before July 1, 1995 are copyrighted until 70 years after the death of the author. See Übergangsrecht. Please use this template only if the author never claimed authorship or their authorship never became public in any other way. If the work is anonymous or pseudonymous (e.g., published only under a corporate or organization's name), use this template for images published more than 70 years ago.
For a work made available to the public in the United Kingdom, please use Template:PD-UK-unknown instead.
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This Swedish photograph is in the public domain in Sweden because one of the following applies:
For photos in the first category created before 1969, also {{PD-1996}} usually applies. For photos in the second category published before 1929, also {{PD-US-expired}} usually applies. If the photographer died before 1954, {{PD-old-70}} should be used instead of this tag. If the author died before 1926, also {{PD-1996}} usually applies. You must also include a United States public domain tag to indicate why this work is in the public domain in the United States. Note that a few countries have copyright terms longer than 70 years: Mexico has 100 years, Jamaica has 95 years, Colombia has 80 years, and Guatemala and Samoa have 75 years. This image may not be in the public domain in these countries, which moreover do not implement the rule of the shorter term. Honduras has a general copyright term of 75 years, but it does implement the rule of the shorter term. Copyright may extend on works created by French who died for France in World War II (more information), Russians who served in the Eastern Front of World War II (known as the Great Patriotic War in Russia) and posthumously rehabilitated victims of Soviet repressions (more information).
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 | This image contains regular noise, texture, or interference which should be cleaned up using Fourier analysis or some similar appropriate method. Beginning with a higher resolution image may help.
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| Date/Time | Thumbnail | Dimensions | User | Comment | |
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| current | 21:41, 23 October 2005 | | 1,552 × 1,818 (279 KB) | Väsk (talk | contribs) | From http://runeberg.org/nfcr/0059.html {{PD-Ugglan}} |
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