File:Bell telephone magazine (1922) (14569325879).jpg

Identifier: bellvol25telephonemag00amerrich (find matches)
Title: Bell telephone magazine
Year: 1922 (1920s)
Authors: American Telephone and Telegraph Company American Telephone and Telegraph Company. Information Dept
Subjects: Telephone
Publisher: (New York, American Telephone and Telegraph Co., etc.)
Contributing Library: Prelinger Library
Digitizing Sponsor: Internet Archive

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
nds from both the nose and mouthreach the microphone. The aviators oxygen mask is simi-larly a noise shield, and actuallyforms the mouthpiece for the micro-iphone. The microphone design wascoordinated with the design of theoxygen mask, and the unit—of either the granular-carbon or magnetic type—was standardized for the Army,Navy, and British oxygen masks. The third method of restrictingnoise from the microphone, and onewhich provides a good degree of dis-crimination between speech and noise,is by the use of the lip microphone.The principle of this microphone isvery simple. If a diaphragm is openon both sides, noise will reach it withsubstantially the same intensity andphase at each side, and therefore willtend to cancel out. Then when onetalks very close to one side of the dia-phragm, the speech will actuate thediaphragm principally from that oneside, and hence the ratio of speechto noise transmitted will be high. This microphone is equipped witha harness so that it can be worn on
Text Appearing After Image:
A souND-POWERED TELEPHONE in usc aboard a U. S. warship 40 Bell Telephone Magazine SPRING s the lip, making the speech path to oneside of the diaphragm very short. Itcan also be used with many of thedevices provided by the military serv-ices, and has been standardized forArmy and Navy use. Sound-powered Telephones Another group of military tele-phone instruments includes the sound-powered telephones. A sound-pow-ered instrument is one which is de-pendent solely on the voice as itssource of energy. No battery orother external power supply is used.The sound-powered transmitter is agenerator which creates the voice-modulated currents transmitted overthe line. At the receiving end thereis a similar instrument in which thetransmitted frequencies are recon-verted into speech. Bells originaltelephone was a sound-powered in-strument. Although the principle of sound-power is not new, the instruments ofthe type used in the recent war havebeen improved by the use of high-grade magnetic alloys, w

Note About Images