A tin can telephone is a type of acoustic speech-transmitting device made up of two tin cans, paper cups or similarly shaped items attached to either end of a taut string or wire. It is a particular case of mechanical telephony, where sound is converted into vibrations along liquid or solid medium. These vibrations are transmitted along the medium and then reconverted back to sound. In the case of tin can telephone the medium is a string.
History
Before the invention of the electromagnetic telephone, there were mechanical acoustic devices for transmitting spoken words and music over a distance greater than that of normal speech. The very earliest mechanical telephones were based on sound transmission through pipes or other physical media, and among the very earliest experiments were those conducted by the British physicist and polymathRobert Hooke from 1664 to 1685. From 1664 to 1665 Hooke experimented with sound transmission through a taut distended wire. An acoustic string phone is attributed to him as early as 1667. The highly similar acoustic tin can telephone, or 'lover's phone', has also been known for centuries. It connects two diaphragms with a taut string or wire, which transmits sound by mechanical vibrations from one to the other along the wire. The classic example is the children's toy made by connecting the bottoms of two paper cups, metal cans, or plastic bottles with tautly held string. For a short period of time acoustic telephones were marketed commercially as a niche competitor to the electrical telephone, as they preceded the latter's invention and didn't fall within the scope of its patent protection. When Alexander Graham Bell's telephone patent expired and dozens of new phone companies flooded the marketplace, acoustic telephone manufacturers could not compete commercially and quickly went out of business. Their maximum range was very limited, but hundreds of technical innovations increased their range to approximately a half mile or more under ideal conditions. An example of one such company was Lemuel Mellett’s 'Pulsion Telephone Supply Company' of Massachusetts, which designed its version in 1888 and deployed it on railroad right-of-ways, purportedly with a range of. In the centuries before tin cans and paper cups became commonplace, other cups were used and the device was sometimes called the "lovers' telephone". During the 20th century, it came into common use in preschools and elementary schools to teach children about sound vibration.
Operation
When the string is pulled taut and someone speaks into one of the cans, its bottom acts as a diaphragm, converting the sound waves into longitudinal mechanical vibrations which vary the tension of the string. These variations in tension set up longitudinal waves in the string which travel to the second can, causing its bottom to vibrate in a similar manner as the first can, thus recreating the sound, which is heard by the second person. The signal can be directed around corners with at least two methods: The first method can be implemented by creating a loop in the string which is then twisted and anchored to another object. Another method makes use of an extra can positioned on the apex of the corner; the string is threaded through the base of the can so as to avoid coming into contact with the object around which the signal is to be directed.
