Colleagues,
I am teaching an intermediate-level lab for our physics majors focusing on
vibrations and waves (text for associated lecture course is Vibrations and
Waves in Physics, by Main).
We are into the project portion of our lab course. I seek information
about percussion devices such as gongs or wind chimes that seem to change
pitch after they are struck. My fuzzy image is of some big-muscled guy in
striking the giant gong and its predominant tone increasing in frequency
during the 1-5 seconds after it is struck.
Probably they are constructed to have two (or more) modes that are the
loudest of all modes and are close together in frequency. Intentionally
damping the lowest-frequency mode to decay faster than the next mode up
would cause the ear to perceive a change in "fundamental" pitch. I imagine
that they might add mass to the locations of the antinode(s) for the lowest
mode which, hopefully, doesn't correspond to an antinode of the next mode
up (in frequency).
Does anyone know about these things--- references, how-to instructions, etc.
I am hoping to get my students to build one, analyze how it vibrates, and
do sliding FFTs of its sound vs. time. If it works well enough, they would
make great Christmas presents.
Thanks!
_____________________________________________________
Dr. Dean Livelybrooks "God is subtle, but he is not
Department of Physics malicious." Albert Einstein
1274 University of Oregon (541)-346-5855
Eugene, OR 97403-1274 USA (541)-346-5861-FAX