Vibrational Modes of the (2,1) Mode

The third main mode of vibration of a circular membrane is the (2,1) mode. This is the second most imporant vibrational mode in terms of the musical quality of the drum. The (2,1) mode vibrates at a freqeuncy 2.135 times the frequency of the (0,1) mode. The nodal point run the diameter of the drum at right angles to each other, making a large X.

The (2,1) mode acts as a four pole sound vibration source, which is less efficient at radiating sound energy than the (1,1) dipole mode and very much less than the (0,1) monopole mode. The lower efficiency explains why the (2,1) mode takes longer to decay, making it an important component of the musical quality of the drum.

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