Cinematographic annual : 1930 (1930)

Record Details:

Title:
Cinematographic annual : 1930
Date:
1930
Publisher:
Hollywood : The American Society of Cinematographers, Inc.
Volume:
Cinematographic annual : 1930
Leaf #:
000369
Language:
English
Subjects:
Motion Pictures, Motion Picture Technology
Collection:
Books
Format:
Books
Contributor:
Media History Digital Library
Sponsor:
{"Media History Digital Library","Richard Koszarski","Jeff Joseph"}
Coordinator:
Media History Digital Library
Description:
Date Added:
March 21, 2024
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RCA PHOTOPHONE SYSTEM 349 0".0015 is the other plate. The diaphragm is made of duralumin rolled to a thickness of about 0".0015 and stretched to a very high tension in a frame, not unlike the embroidery hoops our mothers used to use. The diaphragm is electrically insulated FIGURE 1 Photophone Type R-3 Recorder threaded with film. from the back plate and forms in reality a simple condenser, hence the name condenser microphone. The action is quite as simple as its construction. A fairly high voltage, usually about 180 volts, is impressed across these two plates through a very high resistance. This resistance is usually from 20 to 50 million ohms. As the sound waves strike the diaphragm, it moves back and forth, causing a very slight change in capacity. This change in capacity makes itself evident as an alternating current flowing through the microphone and the resistance. Across this resistance is coupled the first tube of the amplifier, which takes this very tiny electrical signal and increases it to the degree necessary for operating various devices on the other end. These amplifiers are so constructed that one may use almost any number of microphones and combine the output of these