Acoustic telegraph, a.k.a. voice pipe
Exhibit on display in Stanislaw Lem Garden of Experiences, a branch of the Museum of Municipal Engineering in Krakow.
Description written by Adrianna Gajdziszewska
Two persons are needed to perform the experiment with the acoustic telegraph. Stand at one end and ask your companion to go to the other end, following the main path. You are now facing each other and you are about 30 meters apart. Between you, buried in the ground is a pipe. You’re standing in front of the ends of the pipe, protruding from the ground. Stay where you are and try to talk to each other not using the telegraph. Then, bring your face closer to the funnel-like end of the pipe and say something. The other person listens by bringing their ear close to their end of the pipe. Staying in your places, switch roles. Also, check if it is possible to communicate by whispering into the pipe.
How does the acoustic telegraph work?
In an open space, sound waves travel in all directions and their strength diminishes quickly with distance. The pipe you’re standing in front of is, in fact, a waveguide, guiding the soundwave to the receiver, which happens to be your friend’s ear. Such voice pipes were once used for internal communication on ships, in fortifications, offices and residences. Voice pipes have been replaced by telephone communication.