Carbon microphone

How Telephones Work: "How the Telephone Talks" circa 1927 Bray Studios Animated Cartoon

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• published: 20 Sep 2013
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more at http://phones.quickfound.net Animation displays the workings of the early telephone and its carbon microphone. Public domain film from the Prelinger Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied. The film was silent. I have added music created by myself using the Reaper Digital Audio Workstation and the Independence and Proteus VX VST instrument plugins. http://creativecommons.org/licenses/by-sa/3.0/ http://en.wikipedia.org/wiki/Telephone A telephone, or phone, is a telecommunications device that permits two or more users to conduct a conversation when they are not in the same vicinity of each other to be heard directly. A telephone converts sound, typically and most efficiently the human voice, into electronic signals suitable for transmission via cables or other transmission media over long distances, and replays such signals simultaneously in audible form to its user. The word telephone has been adapted into the vocabulary of many languages. It is derived from the Greek: τῆλε, tēle, far and φωνή, phōnē, voice, together meaning distant voice. First patented in 1876 by Alexander Graham Bell and further developed by many others, the telephone was the first device in history that enabled people to talk directly with each other across large distances. Telephones became rapidly indispensable to businesses, government, and households, and are today some of the most widely used small appliances. The essential elements of a telephone are a microphone (transmitter) to speak into and an earphone (receiver) which reproduces the voice of the distant person. In addition, most telephones contain a ringer which produces a sound to announce an incoming telephone call, and a dial used to enter a telephone number when initiating a call to another telephone. Until approximately the 1970s most telephones used a rotary dial, which was superseded by the modern Touch-Tone push-button dial, first introduced by AT&T; in 1963. The receiver and transmitter are usually built into a handset which is held up to the ear and mouth during conversation. The dial may be located either on the handset, or on a base unit to which the handset is connected by a cord containing wires. The transmitter converts the sound waves to electrical signals which are sent through the telephone network to the receiving phone. The receiving telephone converts the signals into audible sound in the receiver, or sometimes a loudspeaker. Telephones are a duplex communications medium, meaning they allow the people on both ends to talk simultaneously. A landline telephone is connected by a pair of wires to the telephone network, while a mobile phone, such as a cellular phone, is portable and communicates with the telephone network by radio transmissions. A cordless telephone has a portable handset which communicates by radio transmission with the handset base station which is connected by wire to the telephone network. The telephone network, consisting of a worldwide net of telephone lines, fiberoptic cables, microwave transmission, cellular networks, communications satellites, and undersea telephone cables connected by switching centers, allows any telephone in the world to communicate with any other. Each telephone line has an identifying number called its telephone number. To initiate a telephone call the user enters the other telephone's number into a numeric keypad on the phone. Graphic symbols used to designate telephone service or phone-related information in print, signage, and other media include ℡ (U+2121), ☎ (U+260E), ☏ (U+260F), ✆ (U+2706), and ⌕ (U+2315)... http://en.wikipedia.org/wiki/Carbon_microphone The carbon microphone, also known as carbon button microphone, button microphone, or carbon transmitter, is a transducer that converts sound to an electrical audio signal. It consists of two metal plates separated by granules of carbon. One plate is very thin and faces outward, acting as a diaphragm. When sound waves strike this plate, the pressure on the granules changes, which in turn changes the electrical resistance between the plates. Higher pressure lowers the resistance as the granules are pushed closer together. As a steady direct current is passed between the plates, the varying resistance results in a modulation of the current at the same frequency of the impinging sound waves. In telephony, this signal is directly passed through a telephone system to the central office, or it is electronically amplified in other sound systems, such as a public address system or a recording device. The frequency response of the carbon microphone, however, is limited to a narrow range, and the device produces significant electrical noise. Before the proliferation of vacuum tube amplifiers in the 1920s, carbon microphones were the only practical means of obtaining high-level audio signals, and were widely used in telephone systems...