Big secret of Big Ben’s famous bong revealed by scientists
RESEARCH engineers from Leicester have used lasers to measure Big Ben’s bong.
The team have produced a unique vibration map of the famous bell in the Houses of Parliament tower to reveal why it produces its distinct harmonious tone.
The group, from the advanced structural dynamics evaluation centre (ASDEC) at the University of Leicester, measured four of Big Ben’s chimes, at 9am, 10am, 11am and noon.
They created a 3D computer model of the bell and used a measurement technique called ‘laser Doppler vibrometry’ to map the vibrations in the metal as it chimed.
The findings were revealed during a BBC documentary Sound Waves: The Symphony of Physics, broadcast last Thursday, March 2 on BBC4.
Martin Cockrill, a technical specialist from the university’s engineering department said: “Aside from the technical aspects one of the most challenging parts of the job was carrying all of our equipment up the 334 steps of the spiral staircase to the belfry. Then to get everything set up before the first chime, we were literally working against the clock.
“Many of the vibrations in the metal of Big Ben are too tiny to be seen by the naked eye. But this is what we were able to map using the lasers and not just one or two points on the surface - we were able to get over 500 measurements across the surface which just wouldn’t have been possible with previous technologies.”
According to the research team, Big Ben is thicker than other bells of a similar size, weighing more and as a result has a higher pitch than expected for its diameter.
When a bell is struck, the impact causes different vibrations or modes. The frequency and intensity of these modes are predominantly affected by the profile of the bell.
Martin said: “This was a once-in-a-lifetime opportunity. You cannot just glue sensors to a national treasure such as Big Ben. Our ability to do the whole thing quickly without touching the bell was key to the whole project.”
Big Ben is the nickname for the Great Bell of the clock at the north end of the Palace of Westminster. It first chimed on July 11 1859.
The tower is officially known as Elizabeth Tower, renamed to celebrate the Diamond Jubilee of Elizabeth II in 2012.