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!

112 sec at say 343ms, that’s about 38.5km. Nice.