Bouncing off of a special electrical layer of the atmosphere called the ionosphere, shortwave radio waves can be heard in many parts of the globe before they're done.  All of this happens at the speed of light, as the radio waves span oceans and countries.  Shortwave radio is not always clear, and sometimes there can be static and hissing sounds in the background:

Isa 5:26  

"And he will lift up an ensign to the nations from far, and will hiss unto them from the end of the earth: and, behold, they shall come with speed swiftly:"