Sometimes the sound of a bell has warbles or beats as a result of the splitting of each partial into two components. Commonly the interval between components is a few cents. These warbles art caused by a non strictly rotation symmetric bell, for instance as a consequence of a local porosity in the bell wall. It is possible to bring both components into coincidence by lowering the higher component. This has to be done with one or more small vertical grooves in the antinodes of that component. Research was done into the correlation between the vertical place of the groove in the bell wall and the amount of lowering of the most important partials of a bell, viz. the five lowest. With the help of the results of this research some examples are given of removing warbles in a bell. To determine the best place and depth of the grooves linear optimisation was an excellent help. [References: 6]
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