An acoustic shadow or sound 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, buildings, or sound barriers.
A short-distance acoustic shadow occurs behind a building or a sound barrier. The sound from a source is shielded by the obstruction. Due to diffraction around the object, it will not be completely silent in the sound shadow. The amplitude of the sound can be reduced considerably, however, depending on the additional distance the sound has to travel between source and receiver.
Anomalous sound propagation in the atmosphere can occur in certain conditions of wind, temperature and pressure. Such conditions enable sound to travel in refraction channels over long distances until returning to the Earth's surface, and it thus may not be heard in intervening locations. [1] As one website refers to it, "an acoustic shadow is to sound what a mirage is to light". [2] 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. [3] 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's documentary The Civil War, produced by Florentine Films and aired on PBS in September 1990. [4] Observers of nearby battles would sometimes see the smoke and flashes of light from cannon but not hear the corresponding roar of battle, while those in more distant locations would hear the sounds distinctly. [5]
Two diarists John Evelyn and Samuel Pepys heard from London the naval guns of the Four Days' Battle, which ranged over the southern North Sea between England and the Flanders coast. However the guns were not heard at all in towns on the coast nearer to the action: [1]
Being in my garden at 6 o'clock in the evening, and hearing the great guns go thick off, I took horse and rode ...next day toward the Downs and seacoast, but meeting the Lieutenant of the Hampshire frigate, who told me what passed, or rather what had not passed, I returned to London, there being no noise, or appearance at Deal, or on that coast of any engagement. Recounting this to his Majesty...he was astonished when I assured him they heard nothing of the guns in the Downs, nor did the Lieutenant who landed there by five that morning. [6]
— Friday 1 June 1666, The Diary of John Evelyn
...so far as to yesterday it is a miraculous thing that we all Friday, and Saturday and yesterday, did hear every where most plainly the guns go off, and yet at Deale and Dover to last night they did not hear one word of a fight, nor think they heard one gun. This...makes room for a great dispute in philosophy, how we should hear it and they not, the same wind that brought it to us being the same that should bring it to them: but so it is. [7] .
— Monday 4 June 1666, The Diary of Samuel Pepys
Garrison Jr., Webb, Strange Battles of the Civil War, Cumberland House, 2001, ISBN 1-58182-226-X Ross, Charles D. "Civil War Acoustic Shadows". Shippensburg, PA: White Mane Publishing, 2001l ISBN 978-1572492547.
Acoustics is a branch of physics that deals with the study of mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical engineer. The application of acoustics is present in almost all aspects of modern society with the most obvious being the audio and noise control industries.
Samuel Pepys was an English diarist and naval administrator. He served as administrator of the Royal Navy and Member of Parliament and is most famous for the diary he kept for a decade. Pepys had no maritime experience, but he rose to be the Chief Secretary to the Admiralty under both King Charles II and King James II through patronage, diligence, and his talent for administration. His influence and reforms at the Admiralty were important in the early professionalisation of the Royal Navy.
In common usage, wind gradient, more specifically wind speed gradient or wind velocity gradient, or alternatively shear wind, is the vertical component of the gradient of the mean horizontal wind speed in the lower atmosphere. It is the rate of increase of wind strength with unit increase in height above ground level. In metric units, it is often measured in units of meters per second of speed, per kilometer of height (m/s/km), which reduces inverse milliseconds (ms−1), a unit also used for shear rate.
Sir William Penn was an English admiral and politician who sat in the House of Commons from 1660 to 1670. He was the father of William Penn, founder of the colonial Province of Pennsylvania, which is now Pennsylvania.
Royal Charles was an 80-gun first-rate three-decker ship of the line of the English Navy. She was built by Peter Pett and launched at Woolwich Dockyard in 1655, for the navy of the Commonwealth of England. She was originally called Naseby, named in honour of Sir Thomas Fairfax's decisive 1645 victory over the Royalist forces during the English Civil Wars. She was ordered in 1654 as one of a programme of four second rates, intended to carry 60 guns each. However, she was altered during construction to mount a complete battery of guns along the upper deck, and so was reclassed as a first rate.
Edward Montagu, 1st Earl of Sandwich, 27 July 1625 to 28 May 1672, was an English military officer, politician and diplomat from Barnwell, Northamptonshire. During the First English Civil War, he served with the Parliamentarian army, and was an MP at various times between 1645 and 1660. Under The Protectorate, he was also a member of the English Council of State and General at sea.
HMS Royal Katherine was an 84-gun full-rigged second-rate ship of the line of the Royal Navy, launched in 1664 at Woolwich Dockyard. Her launching was conducted by Charles II and attended by Samuel Pepys. Royal Katherine fought in both the Second and Third Anglo-Dutch Wars and afterwards, the War of the Grand Alliance before entering the dockyard at Portsmouth for rebuilding in 1702. In this rebuilding, she was upgraded to carry more guns, 90 in total, and served in the War of the Spanish Succession during which she was renamed Ramillies in honour of John Churchill's victory at the Battle of Ramillies. She was rebuilt again in 1742–3 before serving as the flagship of the ill-fated Admiral John Byng in the Seven Years' War. Ramillies was wrecked at Bolt Tail near Hope Cove on 15 February 1760.
John Belasyse, 1st Baron Belasyse was an English nobleman, Royalist officer and Member of Parliament, notable for his role during and after the Civil War. He suffered a long spell of imprisonment during the Popish Plot, although he was never brought to trial. From 1671 until his death he lived in Whitton, near Twickenham in Middlesex. Samuel Pepys was impressed by his collection of paintings, which has long since disappeared.
The Great Fire of London was a major conflagration that swept through central London from Sunday 2 September to Thursday 6 September 1666, gutting the medieval City of London inside the old Roman city wall, while also extending past the wall to the west. The death toll is generally thought to have been relatively small, although some historians have challenged this belief.
Underwater acoustics is the study of the propagation of sound in water and the interaction of the mechanical waves that constitute sound with the water, its contents and its boundaries. The water may be in the ocean, a lake, a river or a tank. Typical frequencies associated with underwater acoustics are between 10 Hz and 1 MHz. The propagation of sound in the ocean at frequencies lower than 10 Hz is usually not possible without penetrating deep into the seabed, whereas frequencies above 1 MHz are rarely used because they are absorbed very quickly.
Sir Lewis Dyve (1599–1669) was an English Member of Parliament and a Royalist adherent during the English Civil War. His surname is sometimes also spelt Dive or Dives.
HMS Assurance was a 32-gun fourth-rate of the English Navy, built by Peter Pett I at Deptford Dockyard and launched in 1646. She was in the Parliamentary force during the English Civil War, then the Commonwealth Navy and was incorporated into the Royal Navy after the Restoration in 1660. During her time in the Commonwealth Navy she partook in the Battles of Dover, Portland, Gabbard and Texel. She foundered in a gale at Woolwich in 1660 and was salved. After the Restoration she partook in the Battle of Lowestoffe, the Four Days Fight and the Texel (1673). She was reduced to a Fifth Rate in 1690 before being sold in 1698.
London was a 76-gun second-rate ship of the line in the Navy of the Commonwealth of England, originally built at Chatham Dockyard by shipwright John Taylor, and launched in June 1656. She gained fame as one of the ships that escorted Charles II from Holland back to England during the English Restoration, carrying Charles' younger brother James Duke of York, and commanded by Captain John Lawson.
In physics, sound is a vibration that propagates as an acoustic wave through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the reception of such waves and their perception by the brain. Only acoustic waves that have frequencies lying between about 20 Hz and 20 kHz, the audio frequency range, elicit an auditory percept in humans. In air at atmospheric pressure, these represent sound waves with wavelengths of 17 meters (56 ft) to 1.7 centimeters (0.67 in). Sound waves above 20 kHz are known as ultrasound and are not audible to humans. Sound waves below 20 Hz are known as infrasound. Different animal species have varying hearing ranges.
Sir Samuel Tuke, 1st Baronet was an English officer in the Royalist army during the English Civil War and a notable playwright. He is best known for his 1663 play The Adventures of Five Hours, possibly co-authored by George Digby – the play was produced by the Duke's Company and later proved an influence on Richard Brinsley Sheridan's opera The Duenna.
Vice Admiral Sir John Mennes was an English naval officer, who went on to be Comptroller of the Navy. He was also considered a wit. His comic and satirical verses, written in correspondence with James Smith, were published in 1656. He figures prominently in the Diary of Samuel Pepys, who reported directly to Mennes at the Navy Office and thought him an incompetent civil servant, but a delightful social companion.
The rebel yell was a battle cry used by Confederate soldiers during the American Civil War. Confederate soldiers used the yell when charging to intimidate the enemy and boost their own morale, although the yell had many other uses. There are audio clips and film footage of veterans performing the yell many years later at Civil War veterans' reunions. The origin of the yell is uncertain.
The Battle of Martinique took place off the Caribbean island of Martinique from 30 June to 7 July 1667, towards the end of the Second Anglo-Dutch War. A French fleet commanded by de la Barre was virtually destroyed by a Royal Navy squadron under Sir John Harman. Victory meant the English restored their position in the region shortly before the Treaty of Breda ended the war on 31 July 1667.
Sir Andrew Henley, 1st baronet (1622–75), of Bramshill, Hampshire was an English politician and the first of the Henley baronets. He is best remembered for his celebrated quarrel with the future Duke of Bolton, which is recorded in the Diary of Samuel Pepys.
The Battle of Ronas Voe was a naval engagement between the English Royal Navy and the Dutch East India ship Wapen van Rotterdam on 14 March 1674 in Ronas Voe, Shetland as part of the Third Anglo-Dutch War. Having occurred 23 days after the signing of the Treaty of Westminster, it is likely to have been the final battle of the Third Anglo-Dutch War.
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