Acoustic Shadow
Encyclopedia
An acoustic shadow is an area through which sound waves fail to propagate, due to topographical
obstructions or disruption of the waves via phenomena such as wind currents. A gobo
refers to a movable acoustic isolation panel and that makes an acoustic shadow. As one website refers to it, "an acoustic shadow is to sound what a mirage
is to light"http://www.unmuseum.org/soearch/over0104.htm. For example, at the Battle of Iuka
, a northerly wind prevented General Ulysses S. Grant
from hearing the sounds of battle and sending more troops. Many other instances of acoustic shadowing were prevalent during the American Civil War, including the Battles of Seven Pines
, Gaines' Mill
, Perryville
and Five Forks
. Indeed, this is addressed in the Ken Burns' documentary "The Civil War" (produced and aired on PBS, September 1990). Persons nearby would see the smoke and flashes of light but not the corresponding roar of battle, while those in more distant locations would hear the sounds distinctly.
Topography
Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...
obstructions or disruption of the waves via phenomena such as wind currents. A gobo
Gobo (recording)
Gobo is a slang term used by sound recording engineers to refer to a movable acoustic isolation panel.An acoustics gobo is parallel in use to a photography gobo, which is used to block direct light sources, and also shares its name with the stage lighting gobo...
refers to a movable acoustic isolation panel and that makes an acoustic shadow. As one website refers to it, "an acoustic shadow is to sound what a mirage
Mirage
A mirage is a naturally occurring optical phenomenon in which light rays are bent to produce a displaced image of distant objects or the sky. The word comes to English via the French mirage, from the Latin mirare, meaning "to look at, to wonder at"...
is to light"http://www.unmuseum.org/soearch/over0104.htm. For example, at the Battle of Iuka
Battle of Iuka
The Battle of Iuka was fought on September 19, 1862, in Iuka, Mississippi, during the American Civil War. In the opening battle of the Iuka-Corinth Campaign, Union Maj. Gen. William S. Rosecrans stopped the advance of the army of Confederate Maj. Gen. Sterling Price.Maj. Gen. Ulysses S...
, a northerly wind prevented General Ulysses S. Grant
Ulysses S. Grant
Ulysses S. Grant was the 18th President of the United States as well as military commander during the Civil War and post-war Reconstruction periods. Under Grant's command, the Union Army defeated the Confederate military and ended the Confederate States of America...
from hearing the sounds of battle and sending more troops. Many other instances of acoustic shadowing were prevalent during the American Civil War, including the Battles of Seven Pines
Battle of Seven Pines
The Battle of Seven Pines, also known as the Battle of Fair Oaks or Fair Oaks Station, took place on May 31 and June 1, 1862, in Henrico County, Virginia, as part of the Peninsula Campaign of the American Civil War. It was the culmination of an offensive up the Virginia Peninsula by Union Maj. Gen....
, Gaines' Mill
Battle of Gaines' Mill
The Battle of Gaines's Mill, sometimes known as the First Battle of Cold Harbor or the Battle of Chickahominy River, took place on June 27, 1862, in Hanover County, Virginia, as the third of the Seven Days Battles of the American Civil War...
, Perryville
Battle of Perryville
The Battle of Perryville, also known as the Battle of Chaplin Hills, was fought on October 8, 1862, in the Chaplin Hills west of Perryville, Kentucky, as the culmination of the Confederate Heartland Offensive during the American Civil War. Confederate Gen. Braxton Bragg's Army of Mississippi won a...
and Five Forks
Battle of Five Forks
The Battle of Five Forks was fought on April 1, 1865, southwest of Petersburg, Virginia, in Dinwiddie County, during the Appomattox Campaign of the American Civil War. The battle, sometimes referred to as the "Waterloo of the Confederacy," pitted Union Maj. Gen. Philip H. Sheridan against...
. Indeed, this is addressed in the Ken Burns' documentary "The Civil War" (produced and aired on PBS, September 1990). Persons nearby would see the smoke and flashes of light but not the corresponding roar of battle, while those in more distant locations would hear the sounds distinctly.