I've had excellent luck getting strong (loud) resonances with tuning forks
and two end open tubes. It takes a bit of time to get them to the right
length to match the tuning fork, but once found they work great. The tubes
are fluorescent tube protectors, 4 or 5 cm wide and thin walled, maybe a
millimeter.
Similarly, if I submerge these same tubes in water in a graduated cylinder,
I can make an adjustable one end open, one end closed tube. I can move the
tubes up and down until the column of air matches the tuning fork and then
have a loud resonance.
What I can't do is get a loud resonance with a tube using an adjustable
disk as a plunger. Why do I want to use a plunger? Many of my students when
interviewed thought the water in the submerged tube was resonating rather
than the air. Careful explanations couldn't dissuade them. This was further
confirmed by our Visitor, Research, and Evaluation group at the
Exploratorium who interviewed dozens of guests who interacted with a
similar exhibit. Only a few people thought the water was making an end
point.
So, I want to make a one end closed, one end open resonator with an
adjustable plunger. My design is a wooden plug cut to fit the tube with a
small wrapping of felt to let it slide. It works okay, but not nearly as
well as the two ends open version or the one end open version and water.
I don't understand why. Anyone have an idea? And do you think that this is
related to the fact marimbas almost always use two end open tubes for
resonators?
--
*Marc "Zeke" Kossover | Educator, Exploratorium*
zkossover@exploratorium.edu
Museum: Pier 15, San Francisco, CA 94111
Mailing: 17 Pier, Suite 100, San Francisco, CA 94111