Divine shout.

We know that sound spreads in all directions and therefore weakens very quickly; with the help of a horn, it can be directed mainly in one direction, in which it is desirable to transmit sound with greater force. They have been working on the mouthpiece for hundreds of years, but have come to the conclusion that the simplest mouthpiece is still best. It can easily be made from a folder **. Sew or glue a 2-meter-long tube from a smooth folder so that one end is 15-20 cm in diameter and the other 3 cm, that is, a conical shape. Glue a small funnel to the narrow end of the tube. The walls of the horn will not allow the sound to dissipate, and from this its strength does not weaken noticeably to a very distant distance. If the pipe is 2 m long and well glued, then you can talk at a distance of 1 km (1000 m), and in calm weather, and even at night, even further. A voice coming from a shout

** It is possible from glued with wallpaper glue in several layers of newspaper sheets or paper wallpaper. - Note ed.
Science and Life
If I am not mistaken, this mouthpiece was described in a book about Robert Wood.