Tin can telephone

A tin can phone is a type of acoustic (non-electrical) 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.

Before the invention of the electromagnetic telephone, there were mechanical acoustic devices for transmitting spoken words and music over a greater distance, faster than the speed of sound in air.

During the 20th century, they came into common use in preschools and elementary schools to teach children about sound vibration.

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 is to create a loop in the string which is then twisted and anchored to another object.

Fig 7 Le Telephone by T du Moncel Paris 1880 (Large)
An 1886 advertisement for an acoustic telephone
A section of string contains a number of twists which lead to a loop secured to the back of a chair.
An example of using a twisted loop to direct the string of a can phone into a new direction