Talk:Acoustic shadow

Other Instances
A more recent example that I can personally attest to was in 1980. The May 18 eruption of Mt. St. Helens was not heard in Portland, about 50 miles to the SW, but heard to the east (downwind) many times further away. CFLeon 05:39, 25 July 2007 (UTC)

I can’t testify directly to the acoustic-shadowing effect, but I can testify to the distance modern Naval artillery can sometimes be heard. As a boy in the 1960s-70s, I grew up on a farm in Bryantown MD, which was 19 miles distant from the Naval Support Facility in Dahlgren VA. This is the Navy’s "long ballistic range on the Potomac River, required for the testing of modern, high-powered munitions", where a variety of Naval gun tubes would be fired into a restricted area of the river. On some mornings when tests were occurring, reports of artillery fire could be heard in the distance on my family’s farm. The sound was subtle, low-frequency, and quite distinctive; it would have traversed the mile width of the Potomac, then over 18 miles of heavily wooded Eastern deciduous forest. This wasn’t a daily occurrence but a relatively frequent one. Theophilus Reed (talk) 17:01, 4 July 2020 (UTC)

Physics
I'd like to see a better explanation of the physics involved. "Wind" does not seem likely (at least to me) as a causal factor in creating a "sound shadow" anymore than it would affect a "light shadow". Differences in air density due to temperature differences, would seem to be a more likely causal factor. In the ocean "sound shadows" are also created, but their cause lies in temperature differentials between different masses of water. 13:14, 1 July 2017 (UTC) — Preceding unsigned comment added by TwelveGreat (talk • contribs)

I think you'll find an explanation in the Wikipedia article on Wind Gradient, | here: it is an effect caused by refraction rather than the wind blowing away or cancelling out the sound. In fact, that article deals so much better with the issue that the two articles ought to be either linked or merged. As I am not up to the job of doing a merge, I'll add a prominent link. Thomas Peardew (talk) 17:13, 13 December 2019 (UTC)

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Four Days Battle
There seems to be some confusion about where this battle was fought, which is hardly surprising as it is the longest recorded naval engagement of the age of sail. The Wikipedia page is surprisingly unspecific, though the lede says it started just off the coast of Flanders and ended "near the English coast". Pepys is surprised that the noise wasn't heard in Deal or Dover, which were presumably relatively close to the action at some time, but was heard in London (which was further away). Pepys' diary makes it clear that the day on which the guns were heard in London was 2nd June 1666: at the time Pepys was in the park at Greenwich (ie on high ground). There's little doubt that the guns were in fact heard in London, as John Evelyn heard them too.

There's a fairly recent book, The Command of the Ocean (2004), by the naval historian Nicholas Rodger. It is not amongst the sources for the Wikipedia entry for the battle - the main source there is Fox, which I don't have access to. Rodger makes it clear (Chapter 5) that the battle in fact started in the outer Thames estuary just off the coast of Essex - to the east of the Long Sand Head - and then moved during 1st June 1666 to the Flanders coast. The battle was re-commenced on the morning of 2nd June off the Flanders coast, and by the 3rd the fighting was taking place near the Galloper shoal, where Ayscue's flagship, the [|Royal Prince], ran aground. The Galloper is about 30nm east of Felixstowe. On the fourth day the English ships retreated into the Thames Estuary. Unfortunately Rodger does not say precisely where the battle was fought during the second day, and I don't have access to Fox's comprehensive account of the battle.

The reference to North Foreland in the Wikipedia page for the battle is for the subsequent action on 25th July 1666, the St James' Day Battle.

It would probably be better just to say that battle was fought "between the Thames estuary and the Flanders coast". Thomas Peardew (talk) 14:54, 16 June 2020 (UTC)


 * I think mentioning the Thames estuary would be confusing. It could refer to any point on the estuary, which itself is undefined but might reasonably be considered to terminate at Sheerness. Hearing guns located at Southend from London but not from Dover would be a very different matter to hearing guns located in the middle of the sea from London but not from Deal.


 * Pepys is clear that for three entire days they were heard in London, 1st to 3rd, but that in all that time they were not heard at all in Deal and Dover: "(writing on Monday the 4th) 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"


 * Fox writes extensively about where the battle commenced on Friday 1st of June, and like contemporary accounts, he works in terms of North Foreland:


 * "Among the more reasonable accounts, de Ruyter's journal gives the position as seven miles E.N.E. of the North Foreland and nine miles N.N.W. of Dunkirk, while a letter from Hendrik Hondius, Tromp's flag-captain in the Hollandia, had it to the North-Westward, and at nine or ten miles distance from Ostend'. These two reports at first seem no better than the others - until it is realized that the old Dutch mile, or mijI, was equivalent to four English nautical miles. When the corrected ranges are plotted, the points fall in an area some ten to fifteen miles W.N.W. of the initial early morning anchorage. This is a reasonable distance for the fleet to have covered in the two to two-and-a-half hours it had been under sail, and is also in the right direction. In view of the geometry of the situation when the fleets met, the most probable position is the one reported by de Ruyter, twenty-eight nautical miles E.N.E. of the North Foreland."


 * "The position of Albemarle's fleet was also variously reported. The official English account agrees with Lieutenant Digby's journal that Albemarle's fleet spent the night of the 31st with 'the North forland being 5 Leagues [fifteen miles] from us bearing N.W. & by W'. It continues, 'ther being a fresh gale at S.W. on Friday the first of June at 4 in the morning wee weighed & stood Northward untill 6 in ye morne when the North forlands bore S.W. by S. 6 Leagues off.' This is absurd, since it made the fleet cover twenty-three nautical miles in only two hours. Other reports say that the English went north without event until 7, which implies three hours' sailing rather than two, while the London Gazette placed them four leagues (twelve nautical miles) from the North Foreland when the Dutch were discovered. Probably as good a way as any to determine the northernmost English position is simply to mark off three hours' sailing from the initial point, allowing a good pace of six or seven knots because of the strong breeze on the quarter. That would put the fleet about seventeen miles N.E. of the North Foreland, and in all probability about the same distance W. by N. of the Dutch."


 * I think it's clear from this that the battle commenced to the north and east of North Foreland. Rodger would concur if he has it east of Long Sand Head, which is some 18 miles directly east of Clacton (40 miles north of Deal and 80 miles ~ENE of Hyde Park). All accounts then have it moving SE towards the coast of Flanders. As it comes back to Galloper on the 3rd, it has all the time stayed east of Kent, ranging from NE to SE. I'd love to know how close the fighting got to Deal, but it's not clear from Fox's account. Perhaps we could reword the article to "the Four Days' Battle, which ranged over the southern North Sea, between England and Flanders". This gives as wide a field as possible from the Strait of Dover up to the Suffolk coast, without incorrectly suggesting any fighting taking place west of North Foreland towards the estuary.Pontificalibus 16:17, 16 June 2020 (UTC)


 * Thank you for this: it's very comprehensive - so good that maybe you should tackle the Four Days' Battle page too? But how about two more words: "the Four Days' Battle, which ranged over the southern North Sea, between England and the Flanders coast", as this helps to point out how unusual it was that the guns weren't to be heard in Dover and Deal, which actually face Flanders. Thomas Peardew (talk) 20:09, 16 June 2020 (UTC)
 * Yes, that's great. I'll have a look around and see if I can find anything else on locations during the battle and see about revising the battle article.Pontificalibus 20:43, 16 June 2020 (UTC)