How Are We Able to Hear Through Speaking-Tubes?
We know that when we speak, the sound waves that we set in motion are carried in every direction. Now when we speak into a tube, the sound waves cannot travel in all directions, but must follow the tube, and so we can hear through a tube at a greater distance than we can when speaking in the usual way.
The use of a megaphone or speaking trumpet for conveying the sound of the voice to a distance is based on the same principle.