Tim McNamara said:A Muzi said:A customer asked which bell is loudest when wet.
Until today I did not know thin bike bells don't ring well when wet. Try
it - a schpritz of Windex will do.
Wow. I had no idea. But then I haven't had a bike with a bell in
decades so I guess that's no surprise.
We'll have to put Carl Fogel in charge of ferreting out how this works.
I spent some time googling around with no luck in finding an
explanation. Obviously the moisture on the bell results in a very rapid
decay of the note (I hesitate to use the word "damping" for obvious
reasons... huh, I wonder if this is where the term actually comes from).
Dear Tim,
A bell works by vibrating hard, dense metal against extremely thin,
soft air.
The energy you put into the bell with a tiny hammer mechanism causes
the bell to vibrate until friction (mostly against the air, but some
internal friction) causes the vibration to die away. The hard metal
vibrates nicely, with little internal loss, causing waves in the thin
air that your incredibly sensitive ears can pick up.
If you touch a small bell with your finger, the sound stops instantly
because the energy is absorbed and dissipated by the soggy mass at the
end of your finger.
The energy is so tiny (despite the apparentlyl loud noise picked up by
our sensitive ears) that you scarcely notice how your finger jiggles
when you touch a tiny bell, but you can feel it if you ratchet a bike
bell a few times with your finger on it--your finger feels the bzzz!
of the hammer striking and your ears notice that the sound has almost
vanished.
If you cover the hard metal surface of a bell with something less
hard, like cloth or water, then you damp the vibration, adding more
friction, so the sound dies away much more quickly. The energy goes
into uselessly jiggling the cloth or water in aimless directions and
greatly reduced rates that produce little in the way of sound waves in
air. Strike a bell and the hard metal resonates back and forth. Strike
a cloth punching bag, and the energy dissipates in all directions,
rearranging millions of cotton fibers in different directions.
A larger bell makes more sound when wet for several reasons.
First, the mass of the bell is much larger, compared to the film of
water on its surface, so there's less damping (pun resisted).
Next, a larger bell usually employs a bigger hammer mechanism, so
there's more energy and a louder initial sound.
Finally, smaller bells are higher-pitched instruments, which aren't as
loud to start with for practical reasons and are more easily damped.
For example, a piccolo is not as loud as a tuba, and you can damp a
violin string with one careless fingertip, but not the four-foot bass
tube of a pipe organ.
Cheers,
Carl Fogel