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I think they've got this one wrong...
http://www.bbc.co.uk/news/uk-scotland-highlands-islands-25757937
A new world record for the longest echo in a man-made structure has been set in an underground fuel depot constructed in Scotland before World War Two.Salford University acoustic engineer Prof Trevor Cox recorded a shot fired from a pistol loaded with blanks inside Inchindown tunnels near Invergordon.
The time for the reverberation to end was 112 seconds.
I bet if I ask "what tyres" on STW it'll reverberate for a lot longer than that!
Surely if it's a "man made echo" then just use some kind of delay unit which feeds back and it will echo for ever...
echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...echo...
Pistol?
He should have tried a duck!
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112 sec at say 343ms, that's about 38.5km. Nice.