Vibrational modes of drumheads in various types of drums

As vibrating systems, drums can be divided into three categories: those consisting of a single membrane coupled to an enclosed air cavity (e.g., kettledrums); those consisting of a single membrane open to the air on both sides (e.g., tom toms, congas); and those consisting of two membranes coupled by an enclosed air cavity (e.g., bass drums, snare drums). In kettledrums, the enclosed air raises the frequencies of the axisymmetric modes while air loading lowers the frequencies of the musically important modes with one to four nodal diameters, and shifts them into a nearly harmonic series. In two‐headed drums, coupling of the two heads through the air cavity results in mode pairs in which the heads move either parallel or antiparallel to each other. Dipole, quadrupole and other multipole symmetries are observed in the radiated sound fields. Some drums, such as the kettledrum and tabla, convey a strong sense of pitch; others such as the bass drum and snare drum do not. The sense of pitch may be enhanced by loading a portion of the drumhead, as in the Indian tabla and mridanga.