Salford professor discovers world’s longest echo
Jan 16, 2014
The University of Salford’s Professor of Acoustic Engineering, Trevor Cox, has broken the world record for the longest echo.
The 1970 Guinness Book of Records holds 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, Professor Cox discovered another place in Scotland where the sound echoes for a full minute longer, at an oil storage complex at Inchindown, near Invergordon.
The tanks (pictured right) were secretly constructed deep in the hillside during the 1930s in response to concerns about the strengthening of Germany’s armed forces and the threat posed by long-range bombers.
As there are no doors, Professor Cox entered the tank through one of the 18 inch diameter oil pipes. The tank can hold 25.5 million litres of fuel and has walls 45cm thick. The space is 9 metres wide and 13.5 metres high - about twice the length of a football pitch. Trevor’s singing and shouting brought the giant musical instrument to life.
Professor Cox of the School of Computing, Science & Engineering said: “Never before had I heard such a rush of echoes and reverberation. I was like a toddler sitting at a piano for the first time, thrashing the ivories to see what sounds would come out.
“Reluctantly, after a few minutes I stopped playing with the acoustics and started preparing for my measurements. My initial reaction was disbelief - the reverberation times were just too long.”
His guide was Allan Kilpatrick, an archaeological investigator for the Royal Commission on the Ancient and Historical Monuments of Scotland. 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 - a standard technique used in concert hall acoustics.
At 125 Hertz, a frequency typically made by a tuba, the reverberation time was 112 seconds. Even at the mid-frequencies important for speech, the reverberation time was 30 seconds. The broadband reverberation time which considers all frequencies simultaneously was 75 seconds. They had discovered the world’s most reverberant space.