Why bells ring out danger and celebration instead of ting like triangles
December 26, 2018 9:44 AM   Subscribe

Some lines from a book I'm reading got me wondering about the physics of bells. The vibration and reverberations of bells are mathematically more complex than most other musical instruments. Is there an optimal shape/design?

In case you're interested, the curiosity-provoking lines are from Lies Sleeping by Ben Aaronovitch:
"The hum of a bell is two octaves below its nominal pitch, and is one of the partial tones that give traditionally built bells that sense of depth when they ring. It's why they ring out danger and celebration and the call to prayer and don't go ting the way triangles do — however big they are."
posted by dancing leaves (6 comments total) 34 users marked this as a favorite
 
Once again in MF, a nice chewy post about something I'm totally ignorant about, but read in case some of it will osmose into my brain. Of course, the subject immediately brought to mind the novel The Nine Tailors by Dorothy L. Sayers, which has a lot to do with change ringing, a peculiarly English hobby. Here's a review, with interesting comments, by another good writer, Laurie King: 9 Tailors review. Thanks for an interesting post.
posted by MovableBookLady at 11:16 AM on December 26 [4 favorites]


This is neat; I've never really thought about the actual acoustic mechanisms of bells before now. The notion that the vibration is essentially a circular waveform wrapped around the circumference of the bell feels obvious once it's laid out there but hadn't occurred to me before. I'm perfectly comfortable thinking about overlapping overtone action on e.g. a guitar or piano string but make that a stack of bands of circular bell material oscillating at different rates and I'm suddenly slightly dazzled.

The discussion in the first link of overtones and how to refer to them was a little maddening to me because that off-by-one counting discrepancy is needless recipe for headbutting. The harmonic series isn't a mysterious thing! It doesn't need to have house jargon! It was also odd to me seeing them call that harmonic tone "the twelfth" when I'm so accustomed to thinking of it as a fifth above the octave, but maybe that's just my idiolect.
posted by cortex at 12:43 PM on December 26 [2 favorites]


Bell bronze (commonly called B20) is used in traditional cymbal making - as a drummer and a cymbal enthusiast I've been enjoying the different expressions this metal takes on in it's various molds.

To read that they remove metal from the inside of the bell to tune it recalls the process of lathing the surfaces of a newly cast cymbal to "tune" it. I wonder if they lathe the inside of bells?
posted by djseafood at 2:31 PM on December 26 [1 favorite]


"In case you're interested, the curiosity-provoking lines are from Lies Sleeping by Ben Aaronovitch..."

Ha! Totally guessed it before opening the thread, but just before I did I thought, nah, too unlikely. I feel a sense of irrational accomplishment.

That part piqued my interest, too, so thanks!
posted by Ivan Fyodorovich at 5:38 PM on December 26 [1 favorite]


It was also odd to me seeing them call that harmonic tone "the twelfth" when I'm so accustomed to thinking of it as a fifth above the octave, but maybe that's just my idiolect.

yeah that's like the third harmonic on a string right? The one at the seventh fret of a guitar or bass. Calling it the "twelfth" confused me because I thought they meant the twelfth of the harmonic series, not octave + fifth. I guess you usually hear about 11ths and 13ths in chord construction, so it's natural enough to call that interval a twelfth.

So, if I understand this right, the bell has undertones, if you will, below the fundamental, but vibrating strings do not?
posted by thelonius at 6:51 PM on December 26


So, if I understand this right, the bell has undertones, if you will, below the fundamental, but vibrating strings do not?

My takeaway is that this "hum" is essentially a harmonic resonance an octave below the note caused by the impact of the clapper, which actually does sort of explain the confusion in the jargon - it makes sense to treat the hum as the fundamental, since it's the lowest frequency being sounded. But if you shrink the same shape below a certain point that tone disappears. Because physics!

I think you could get a string to resonate below the initial frequency, if the instrument had an equal amount of string on either side of the bridge. The instrument itself can certainly produce lower frequencies than the plucked note, as you find out the hard way pointing a mic right at the sound hole of an acoustic guitar - that sucker's a bass port.

It was also odd to me seeing them call that harmonic tone "the twelfth" when I'm so accustomed to thinking of it as a fifth above the octave, but maybe that's just my idiolect.
B'lieve that is a "perfect twelfth" harmonically. My brain always struggles with this because guitars are tuned weird.
posted by aspersioncast at 9:40 AM on December 29


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