While writing the previous post, about sound and warfare in Iraq, I came across a brief description of something called an acoustic shadow and its occurrence during the American Civil War. 
An "acoustic shadow" is when the sounds of an event—here, a battle—cannot be heard by people nearby—say, in the neighboring valley or a parallel city street—but those same sounds can plainly be heard over much larger distances. This effect is caused by "a unique combination of factors such as wind, weather, temperature, land topography, forest or other vegetation, and elevation," we read. For example, "battle sounds from Gettysburg fought on July 1, 2, and 3, 1863 could be heard over one hundred miles away in Pittsburgh, but were not heard only ten miles from the battlefield."
Without my own access to contemporary accounts of these battles and their acoustic shadows—sonic phantom limbs haunting distant landscapes—I simply have to trust the accounts that I'm quoting from here; nonetheless, these stories are fascinating. "More than 91,000 men were engaged in battle at Gaines's Mill, Virginia on June 27, 1862," for instance. "Confederate commanders and troops were less than two miles from the battlefield and could plainly see the smoke and flashes from the guns and artillery, but not a sound could be heard of the battle for two hours. Strangely, the battle sounds from the Battle of Gaines's Mill were easily heard in Staunton, Virginia over one hundred miles away."
The unexpected atmospheric reflection of sound, and sound's complicated relationship with certain topographies, levels of humidity, climatic systems, and more presents an amazing—if impossibly complex—dimension to the future of urban design and landscape architecture. Could 5th Avenue be retrofitted to cultivate acoustic shadows—or might a neighborhood in eastern Brooklyn someday find itself overhearing distant traffic events and individual human conversations that have been carried on the winds from Midtown, acoustic effects soon traced back to the mirage-like venting of a new steam plant on the East River?
This also makes me wonder if instances of ghostlike visitation in ancient times—a king crazed by invisible whispers in his fortified tower bedroom, a city cursed by nocturnal voices, a village terrified by bodyless beasts unseen by any hunter—might actually have been examples of acoustic shadows. How could acoustic shadows be archaeologically and historically investigated without exactly reproducing the landscape topography and climatic conditions of the time?
(Vaguely related: a very old post about sound mirrors).
