Corded phone
A corded phone (also Dosentelefon , Bindfadentelefon ) is a toy that can be built with easily accessible means.
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It consists of two empty cans or cardboard or plastic cups that are open on one side and that are mechanically connected with a length of several meters, freely stretched cord or wire. The two ends of the cord are each passed through a central hole in the bottom of the can and prevented from slipping out again by means of a knot .
The sound that enters the opening of one can excites the bottom of the can to flexural vibrations and, when the cord is taut, is transmitted as a longitudinal wave to the other bottom of the can, where it is converted back into quiet, audible airborne sound. Sound can be transmitted in both directions at the same time, but in practice people tend to speak alternately because the can is held directly to the ear for better hearing. The cans act as a resonator when speaking as well as when listening in a narrow frequency range and thus adjusts impedance .
The transmission quality is poor due to the stiff, heavy bottom of the can, because this means that both low and high frequencies are poorly transmitted to the cord - however, voice communication is possible.
Corded telephones are considered to be the child's forerunner of the telephone via electrical line, which also enables bidirectional speech. The simplest electrically transmitting telephony device consists of a dynamic loudspeaker that acts as a microphone, a connected, longer 2-pole cable and a second loudspeaker of the same construction that reproduces the generated alternating current at the other end of the line as a sound. Like the socket telephone, this arrangement does not require any auxiliary power.
The first experiment documented in writing seems to come from Robert Hooke in 1664. He wrote then:
"I have, by the help of a distended wire, propagated the sound to a very considerable distance in an instant"
The collection of the National Museum of the American Indian contains a corded telephone from the Andes that is around 1200 to 1400 years old.
See also
Individual evidence
- ^ Robert Hooke: Micrographia. 1665, accessed December 16, 2013 .
- ↑ Neil Baldwin: There's a 1,200-year-old Phone in the Smithsonian Collections , Smithsonian magazine, December 2013, accessed December 11, 2013.
