Ringing the changes in cultural heritage
Bells are among the oldest of musical instruments and are of deep founded cultural and spiritual significance to European societies. An effort is now under way, using modern technical techniques, to preserve, restore, and improve the continent's bells, including some over 800 years old.
The bell tower on the monastic island of Reichenau, off the shore of Lake Constance in Southern Germany, is part of a UNESCO world heritage site. The oldest bell here was cast in the year 1361.
Kurt Kramer is a campanologist, a bell expert, and has come to Reichenau to analyse the state of the bells. Kurt, who has been studying bells for 40 years, distinguishes between understanding the physics of a bell by means of electronic measurements and understanding the true sound and character of the bell through close, hands-on examination. His tools include various tuning forks to measure and identify different bell tones.
Michael Plitzner is a mechanical engineer with a more high-tech approach using sensors, microphones, accelerometers and computers. He is part of the European research project Probell, a project which aims to understand the physical, mechanical and sonic properties of historic bells. This knowledge should aid in the conservation of these cultural treasures.
An important analytical step is determining the hardness of the bronze used in the bell's casting and the hardness of the clapper's impact zone. By measuring the ringing characteristics of the bell while it is tolled, engineers can analyse the intensity of the clapper impact, the acoustic pressure on and after the impact, and the partial sound wave deterioration. With the acoustic data the bell's expansion or reaction to vibrations can be measured.
The project is being coordinated at Kempten University of Applied Sciences by mechanical engineer Andreas Rupp. Across Europe bells are being tested and analysed.
The bells from different countries have their own unique characteristics. Spanish bells, for example, have a dynamic weight system so that the bells fully rotate on themselves. On the other hand, French and German bells may appear to be identical, but have a different casting process (the French bells are moulded upside down).
The results of the project’s first three years will now allow for warnings if there is a risk of cracking in the bell. The detection of a significant state of deterioration of the impact zone could also, with a timely repair, save a bell.
It can also be determined if a bell is being properly struck to yield the best quality of sound. Complex mathematical models are used to help researchers understand how sound vibrations travel through the bells. A clapper should be designed so that it strikes at exactly the right moment, when the bell reaches the zenith of the arc, and just hard enough to obtain the bell's optimal resonance.
These results will lead to new standards for the casting of new bells today. For the first time, technical standards will be possible for the mechanical details of new bells. Bell makers warn, however, that too much standardisation could mean a loss in common heritage. “Each country must preserve something specific.” [Hanns Martin Rincker, Bell Founder].