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A study of the metallophones of the Balinese gamelan gong kebyar is described here, in which the relationship between their acoustic properties and their sense of pitch are investigated. First, acoustic recordings of the gamelan metallophones were made to analyse their spectral qualities—specifically, the ratios of overtone frequencies to the fundamental and their relative amplitudes. To compare the measured values to theoretical predictions, physical measurements of one of these instruments were also made, the dimensions of the bars supplying values for the frequency equation for transverse waves in a bar.
Results showed that the gamelan metallophones have a distribution of overtones close to that predicted for transverse waves in a straight solid bar, with ratios similar to those in a western glockenspiel. Since the modes of vibrations form non-harmonic overtones and thus do not provide “support” to the fundamental pitch as in a string or a pipe, pitch in gamelan metallophones must be reinforced by other means. Two properties are hypothesized to work in tandem: amplification by bamboo resonators underneath each bar, and the Balinese practice of pairing instruments detuned from each other in such a way that the two pitches are perceived as one (the so-called “chorus effect”)
To test these factors, additional recordings were made in which, respectively, the resonators were covered with felt, and the two paired instruments were played simultaneously. Results showed that resonators significantly strengthen the fundamental pitch, particularly in the metallophones struck with hard mallets. Spectral analysis of the paired recordings reveal that the two “peaks” from the fundamental of each member actually merge into one, with the result that the listener hears one “averaged” pitch with shimmering interference beats that enrich the overall timbre.
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Kim, Sun Bin, "Acoustic Properties of the Balinese Metallophone" (2013). Senior Projects Spring 2013. 394.