When the Whispering Wall was built over a 100 years ago, no one had a clue about its amazing acoustic properties. The concrete dam was constructed by about 400 workers over the South Parra River in Barossa Valley between 1899 and 1902. The dam holds back the 4,515-mega liter Barossa reservoir that supplies water to several areas in southern Australia. The Whispering Wall has always been famous – the 9 storey structure was the first arch dam to be constructed in the region and at one point, the highest in all of Australia. But little did the builders know about the hidden properties of the engineering marvel they had created.
Because the dam is a hard and curved surface, any sound made on one end travels completely unobstructed to the other end. So you could have a perfectly normal conversation with someone standing on the opposite end of the dam (about 450 ft. away), as though they were right next to you! The voices can be heard quite clearly due to a phenomenon known as the parabola effect. The wall is so perfectly curved that it forms one sector of a circle. And the sound waves just bounce in a series of straight jumps all the way to the other end.