Author: Andrew Grantham

Abbot’s Cliff hum and gusts

Posted on by Andrew Grantham

A 75 second recording of the wind at the Abbot’s Cliff sound mirror on 2 April 2009 by Steven Rowell. Evident in this recording, with mic placed directly on concrete mirror concave face, is a noticeable, resonant hum below 150Hz. Wind gusts on the cliffs were quite strong.

It is from radio aporee ::: maps

an open project about the creation and exploration of public soundscapes. it collects and organizes recordings of daily surroundings and other sonic habitats from all over the world. the sounds are organized within a mashup system of mapping software, databases, telephone networks and the Internet. sites and sounds can also be explored and accessed in situ by recent GPS-enabled mobile devices.

Kilnsea sound mirror pictures at From The Neolithic To The Sea

Posted on by Andrew Grantham

Kilnsea Sound Mirror at From The Neolithic To The Sea.

This is a personal journey through time and space, visiting many places and the story told in pictures and words. As with most journeys, we encounter the ordinary, the unusual and the interesting. Some we seek, some we find and some even find us.
From The Neolithic To The Sea: A Journey From The Past To The Present

Other pages of interest on the site include the Humber Port War Signal Station at Spurn, Reighton Sands and the Godwin Artillery Battery at Kilnsea.

Drop Redoubt

Posted on by Andrew Grantham

An open weekend on 30-31 May 2009 allowed the public to visit the Drop Redoubt, a fortress situated on Dover’s Western Heights.

One of the most important and impressive fortifications in Britain, the Western Heights are a series of strong points linked by miles of ditches on the western hilltop above Dover. They were originally begun during the American War of Independence, were strengthened during the Napoleonic Wars and updated and strengthened again in the mid nineteenth century.
Western Heights Preservation Society

Open days are infrequent, but it is well worth a look around if you get the chance to visit. There are no sound mirrors(!), but the redoubt is very impressive, with immense walls surrounded by deep ditches. The entrance drawbridge is gone, so access is via a tunnel into the moat, and then into the fortress building through a sally port.

There were various re-enactors there and a vintage bus service from the town to the redoubt – though it isn’t far to walk.

Conservation of the concrete mirrors

Posted on by Andrew Grantham

When I went on one of the guided walks to the Denge sound mirrors, one of the other vistors was a construction worker who was somewhat critical of the quality of some of the original concrete on the mirrors. I’m not qualified to comment, but Rowan Technologies has some experts on the conservation of concrete.

Case Study #1: Dungeness

English Heritage has commissioned a series of investigative repairs on the mirrors – which are now scheduled as monuments (legal protection specifically for archaeological sites) – that will explore treatments that might be transferable elsewhere. The richly patinated surface of the mirrors is a complex amalgam of weathered aggregate and many varieties of lichen. Chris Wood from English Heritage’s building conservation team is also experimenting with yoghurt to encourage lichen reinstatement. The works were carried out by Rowan Technologies.
Source: The Architects’ Journal, 2008-11-24

Rowan Technologies has this to say:

Conservation Case Studies

The Listening Mirrors, Kent
Like-for-Like Concrete Repairs

The three early warning sound mirrors [at Denge] on the Kent coast were built using reinforced concrete in the late 1920s and the early 1930s to detect the distant sounds of enemy aircraft approaching from over the English Channel. The reinforced concrete has deteriorated in the marine environment and many parts of the structure are suffering from corrosion of the reinforcements and the delamination of the concrete cover.

Rowan Technologies undertook a series of trials of various repair and rehabilitation methods to assess their suitability for these monuments. This included ‘model’ patch repairs of the damaged concrete on a like-for-like basis, to achieving a similar texture and surface finish to the original
Source: Rowan Technologies Ltd

‘Hidden things to see and do’ from the Observer

Posted on by Andrew Grantham

The sound mirrors – and this website – got a mention in the Observer’s travel section on 5 April 2009. The piece formed part of the Military sites” category in a series about Secret Britain – “All around us lie overgrown and forgotten sites with fascinating stories to tell, says Iain Sinclair”.

Acoustic mirrors, various locations

In the middle of a field in Kilnsea, Yorkshire there is a 15-foot-high concave concrete structure resembling a satellite dish. It’s actually an acoustic (or sound) mirror, used during the first world war to detect enemy engine sounds. They are a common fixture along the British coast, including at Kilnsea (OS map ref: TA 411167), Hythe in Kent (OS map ref: TR138344) and Denge on the Dungeness peninsula (OS map ref: TR070215), which recently featured in the new Prodigy music video, Invaders Must Die.
Source Observer