Hywel Williams took some photographs on a guided walk to the Denge sound mirrors on 4 August 2004: Denge Sound Mirrors – “The Listening Ears”.
I could hear the little steam train pass across in front of me off the sound mirror, GREATLY magnified in sound and apparently in the mirror direction it was traveling. Clearly not a demonstration of aeroplane detection, but also a clear demonstration that these concrete mirrors still work, nearly 80 years after their experimental construction!
Ooo, I’m in one of the photos!
Hywel also has a rather good site about Disused stations on London’s Underground.