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Physics of the African gourd drum


nathanstack15

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This past week, a group called the Saakumu dance troop featuring Bernard Woma came to IHS. Their performance featured multiple instruments that are atypical in the United States. For example, they brought with them an African gourd drum, which looked a lot like a curved marimba. However, a marimba's resonators are hollow pipes, whereas this gourd drum's resonators were gourds, the vegetable. This instrument is played by striking wooden bars with mallets. The work done by hitting the wooden bars with the mallet adds energy to the system at one of its natural frequencies. Tones are caused by vibrating columns of air contained within the gourd. The gourd is a closed end resonator, much like the pipes of a pipe organ, or a bottle. Another thing that I noticed is that the smaller the gourd beneath the wooden bar and the smaller the wooden bar, the higher the frequency of the sound produced.  This makes sense, when considering the fundamental frequency of a closed end resonator. There is one node and one antinode for the whole length of the resonator, meaning that the length of the resonator contains 1/4 of a wavelenth. Frequency is v / lamba, and lamba in this case equals 4L. Therefore, when L decreases, the frequency increases.

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