The Longest Propagation?
When the Krakatoa volcano erupted and exploded in 1883, the sound was actually heard a thousand miles away. Regarding infrasound, the resulting barometric depression circled the earth three times.
A Long Propagation
In 2001 the AZF chemical plant in Toulouse, France, blew up. Acousticians measuring plane noise at takeoff close to the Blagnac airport runway less than 10 km away saw their measuring apparatus overloading, while people in Villefranche, 30 km away, came out of their home thinking they had heard two trucks violently crashing into each other.
Propagation in a Tube
At the end of the 19th century two French physicists decided to make an experiment regarding the speed of sound as a function of frequency. A 2900 m pipe of 3 m diameter was built for that purpose. A large brass instrument tuba was used to generate a loud pulse. It was found that the resulting sound was heard during two returns. While no speed difference was noted (we now know that the speed of sound is not frequency dependent, don’t we?), it was observed that the musical sound was gradually stripped of its higher-frequency contents to the extent that on the last passage, only the fundamental was heard (well, we also know by now that sound attenuation is dependent on the frequency to the power 2).
Propagation along a Curved Surface
Propagation along a curved surface (e.g., a wall or a vaulted ceiling) has been known since the Renaissance . In Paris, one can experience it in most of the older underground stations due to their vaulted ceilings: When sitting on the bench of a platform, it is easily possible to understand the normal voice discussion happening on the bench of the opposite platform.