Demonstration of coupled membrane modes on a musical drum
Musical drums such as tom toms and snare drums typically consist of two circular membranes attached to a cylindrical shell. Due to the enclosed air and the shell itself, a drum with two heads exhibits coupling of the lower frequency membrane modes, while the higher frequency modes of the two heads remain essentially independent. A simple demonstration has been developed that illustrates several aspects of drumhead vibrations, including the distinction between strongly and weakly coupled modes. Methods for determining the relative phases and amplitudes of the coupled oscillations have also been developed. The demonstration is useful at a variety of pedagogical levels and can be supplemented with more advanced experiments, including the use of electronic speckle pattern interferometry to identify the mode shapes on both membranes.