Sonic Wonderland - World's Longest Echo by sonicwonderland

Trevor Cox, Professor of Acoustic Engineering at the University of Salford and author of Sonic Wonderland, has discovered the world record for the ‘Longest Echo’. The 1970 Guinness Book of Records is the last claim for the ‘longest echo’, when the solid-bronze doors of the Hamilton Mausoleum in Scotland slammed shut, it took 15 seconds for the sound to die away to silence. In researching his new book Sonic Wonderland: A Scientific Odyssey of Sound Trevor Cox discovered a place where the sound echoes around for a full minute longer, smashing the previous record.

Trevor Cox travelled to the oil storage complex at Inchindown, near Invergordon, Scotland. These reservoirs supplied the naval anchorage in the Cromarty Firth at the bottom of the hill. The tanks were constructed in great secrecy amid concerns about the strengthening of Germany’s armed forces during the 1930s and the threat posed by long-range bombers, which is why the tanks were dug deep into the hillside. The vast complex took three years to complete. His guide was Allan Kilpatrick, an archaeological investigator for the Royal Commission on the Ancient and Historical Monuments of Scotland.

Trevor had to enter the tank through one of the 18 inch diameter oil pipes because there are no doors. The tank could hold 25.5 million litres of fuel and has walls 45cm thick. The space is about twice the length of a football pitch, 9m wide and 13.5 metres high.

Allan fired a pistol loaded with blanks about a third of the way into the storage tank, and Trevor recorded the response picked up by the microphones about a third of the way from the far end. This is a standard technique used in concert hall acoustics; old black-and-white photographs show a gun being fired on the stage of the Royal Festival Hall when they tested the acoustics back in the 1950s.