Today’s account comes courtesy to us from Luc Rombot’s masterful Singing Bronze: A History of Carillon Music.* I highly recommend his book for any reader interested in the history of bells. It’s a recent publication, so you can still easily purchase it online!
We’ve seen the five lowest overtones in a bell that are tuned by bell founders.
How did bell founders identify those partials before our fancy electronic equipment, software, and even tuning forks? None other than René Descartes leads us to the answer. On August 23, 1638, he writes to his colleague Marin Mersenne, “In Utrecht lives a blind man with a great musical reputation, who regularly plays bells….I have seen how he elicits 5 or 6 different sounds on each of the largest bells, without touching them, but only by coming close to their sound rim with his mouth…” Descartes was referring to Jacob Van Eyck, the city carillonneur of Utrecht, and to Van Eyck’s method of whistling near the bell to elicit sympathetic vibrations or sympathetic resonances. This acoustic phenomenon occurs when a certain frequency played by one object (such as a tuning fork or musical instrument) activates a nearby object to faintly resonate at the same frequency. Not any old object will resonate sympathetically, though. The object that will sympathetically vibrate must have that same frequency present inside it already as one of the overtones. Watch this video for a demonstration with tuning forks (turn up the volume to hear the sympathetic resonance).
So, if you whistle various frequencies near a bell, it will begin to gently vibrate and produce the tone (or “speak” as Van Eyck described it) when you whistle the exact frequency of one of its overtones. This can also be demonstrated with some non-musical objects, like wine glasses!
Jacob Van Eyck had shown Descartes a way to pinpoint the frequencies in a bell, but he also knew how to precisely manipulate the overtones through profile design and by shaving off metal from the inside of the bell. Bell founders had known for a long time about this preferred overtone series in bells and had crude methods for tuning them, but it was Van Eyck who improved the knowledge and methods in order to create well-tuned bells. Van Eyck just needed some collaborators…and he found them in the Hemony brothers. More next time!
* Luc Rombouts, Singing Bronze: A History of Carillon Music (Leuven, Belgium: Leuven University Press, 2014), 85.