A voice pipe (an acoustic telegraph))
You need another person for this experiment. Stand at both ends of the device and try to talk through it. When one person is speaking into the funnel-shaped mouthpiece, the other should put their ear to the receiving end to listen to the words. Try whispering.
Then, try to talk to each other directly (without using the device) and not changing your places.
How it works
In unlimited space, the sound wave travels in all directions and its intensity quickly decreases with distance. The pipe is a waveguide, a conveying structure that directs waves to the receiver, i.e., your ear.
Voice pipes or speaking tubes were used to communicate, e.g., on ships, in fortifications, offices, mansions. They have been superseded by telephone systems.