Tuning Barbells
By Fritz Gellerman
Robbie Rhodes: Thanks for your prompt reply. I'm presently making a set of bells for my North Tonawanda band organ, which plays Wurlitzer 150 rolls. The bells on the Wurlitzer organs are struck at the ends, as are the organs made by Don Stinson. There is a dissonant transient produced when the bell is struck on the end that I find annoying. It can be reasonably well eliminated by striking the bar dead center, so that is my approach on this set.
The material is 1.25 by 3/8 inch cold rolled steel with no cut up. The bars are being cut at a machine shop, the ends milled to within one millimeter of the calculated length, and the mounting holes drilled. Then I will tune them about five cents sharp to allow for a drop in pitch when they are electroplated with nickel. The five cents is a guess, as I have no experience with how the tuning is affected by plating, but I assume it will drop the pitch a little. I'll keep track of what happens so that I can change my computer program to allow for plating.
My tuner is a Peterson Strobe-tuner, and I can see the two octaves above the fundamental as well as an overtone a fourth above the fundamental. The same harmonics and overtone are present on my commercial glockenspiel, on which the bars are cut up in back. I will try to find the third and fifth harmonics and compare the cut-up bar and the uniform cross-section bar.
Have you seen any technical articles on barbells? My only reference is "Music, Physics and Engineering" by Harry F. Olson. He treats only uniform bars. Since cutting up the back lowers the pitch, it probably affects the location of the nodes also. This question of the cut-up is only curiosity for me at the moment, as I have no intention of cutting up the metal bars. However, if I should ever make wooden bars then it would become a practical question.
Fritz Gellerman
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(Message sent Fri 17 Nov 1995, 02:34:32 GMT, from time zone GMT-0500.) |
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