The Inchindown tunnels were excavated into a hillside near Invergordon between 1938 and 1941, built to provide a bombproof fuel supply for the Royal Navy base on the Cromarty Firth. Six enormous tanks, each 237 metres long and 9 metres high, were blasted from solid rock, with concrete walls up to 18 inches thick. The facility remained in operation until the 1980s.
In 2014, acoustic engineer Trevor Cox measured the reverberation inside the tunnels and established a new Guinness World Record: 112 seconds at 125Hz, the longest echo ever recorded in a man-made structure. At mid frequencies the reverb lasts around 30 seconds; broadband, approximately 75 seconds.
An impulse response was captured inside the tunnels as part of this project.
