Acoustic and vibrometry analysis of beating in a large Balinese gamelan gong.
David W. Krueger, Kent L. Gee, Jeremy Grimshaw, Dorothy Manuel, Molly E. Jones · The Journal of the Acoustical Society of America · 2009
A large Balinese gamelan gong, the gong ageng wadon, is similar to other Indonesian gongs in that it is tonal. A previously undocumented phenomenon is the fact that this gong produces distinct beating, which is essential to Balinese gamelan music. In this study of Brigham Young University’s gong ageng wadon, acoustical and vibrometry measurements were performed to analyze the source of the beating. Scanning laser Doppler vibrometer results show a beat frequency of about 3 Hz is produced near 150 Hz by closely spaced structural modes. A slightly slower beat frequency (around 2.5 Hz) is also produced at about 120 Hz. The difference in this case is that there is only one structural mode measured near this frequency. It appears that the acoustic radiation from this mode beats with a harmonic of the radiation from a lower structural mode and that this harmonic is caused by nonlinear acoustical phenomena.