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A few people have told me that they can hear the bells now, whereas they couldn’t before the restoration, so I thought it worth explaining how the sound has changed.
Tuning the bells (and replacing those that were too far out to be tuned properly) has improved the sound in two ways. Firstly, and most obviously, the sound is sweeter, because all the different frequencies emitted by the bells are in their proper harmonious relationships with each other. Secondly, and much less obvious, the bells are louder. To understand why, you need to understand something about bell sound.
Like most musical instruments, a bell emits several different frequencies. With an organ pipe or violin string, these frequencies are strictly related to each other (1x, 2x, 3x, etc) corresponding to multiple waves along the pipe or string, and they are called harmonics. With a bell there is no pre-ordained relationship – the bell vibrates in lots of different ways at once, and the frequencies could be anything. Founders have evolved the size, shape and thickness of a bell to bring them approximately in line, but they cannot be exactly controlled in the casting, and are called partials. To tune a bell, the founder carefully removes metal from the inside, taking it from different areas to bring the disparate partials more closely into line.
This ‘scientific’ bell tuning only came into widespread use after our old bells were installed, which is why they were not in tune with themselves, let alone with each other. Now they have been tuned, all the different vibrations work together and augment each other, whereas previously they competed and diminished each other. That makes a much fuller, as well as a richer, sound. They are louder in the tower, with a very pronounced hum, so it is no surprise to hear that they are also audible a little further away than they were before.
John Harrison ( April 2005 )
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