Today, you are talking to us about bells!
Yes, and we will start by looking at the sound emitted by a bell. I think you’ll agree that it’s unlike any other sound! What makes the identity of a sound is the set of notes of which it is made up, what we call the timbre. You know that a sound is nothing other than a vibration of the air, and what is called a note is a vibration of the air at a very precise frequency. For example, the A of tuning forks is a vibration at 440 Hertz, which means that air vibrates 440 times per second. And to achieve this result, it is enough to vibrate the tuning fork, the guitar string or the surface of the bell 440 times per second.
And so each note corresponds to a different frequency?
Exactly. But if we multiply the frequency by 2, we get the same note, but in the upper octave. So at twice 440 Hz, that is to say 880 Hertz, it is also an A. This is called the harmonics of the root note. And if I’m talking to you about that, it’s because on most musical instruments, when you play a note, you also generate harmonics, and it’s this set of notes that gives the timbre of the sound. Well the sound emitted by a bell does not meet these rules. In addition to the fundamental note, we find the first harmonic, but also the note of the lower octave, and two other intermediate notes. For example, if the main note is a C, the other four notes emitted by the bell are E, G, C octave lower and C octave upper.
And all the bells work like that?
Yes, at least the bell-shaped bells that we know in Europe. Because it is their shape that gives them this property. If you tap on any piece of metal, you don’t get a sound! And the shape of a bell is not the result of a scientific calculation, but the culmination of an ancestral art, which dates back several millennia, and whose secret is still jealously guarded today by the founders of Bell. And besides, there are differences in form between the different founders, since manufacturing secrets are not transmitted between founders.
We are in a land of chimes, and therefore we know that we can give a bell the note that we want. How do we do ?
Well, the easiest thing is not to change the general shape of the bell, just multiply its size and thickness by the same factor. In this case, this factor also applies to the frequency of the sound emitted, and therefore the fundamental note is changed. For example, to go from A to A one octave lower, which corresponds to a frequency divided by 2, it suffices to multiply the size and the thickness of the bell by two. Which ultimately gives a bell 8 times heavier. Bells that emit very deep sounds are therefore very large and very heavy. The largest still visible today is 6 meters high and weighs nearly 200 tons. It’s the Tsar kolokol, and you’ll have to go to Moscow to see it.
And at home, there are remarkable bells?
Well, there is Ide, a bell from the Saint-Vaast church in Landas. It is one of the oldest bells in France still in use: it was cast almost 750 years ago, in 1285. But as you said, we are in a land of chimes. Well, the Douai and Tourcoing carillons are among the largest in France, with 62 bells. So you know that an octave has 7 notes, but if we add the sharps and flats, it takes 12 bells to cover an octave. And so with 62 bells, we cover 5 octaves. And suddenly, the lowest bell, the big drone, begins to be very heavy: that of Douai weighs 5 and a half tons! And she gives a la.
