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Snare drums and tom toms used in drum sets often produce an undesirable high frequency ringing sound when struck. Drummers have historically applied DIY damping solutions to address this ringing, placing objects such as wallets and tape on the heads. A large variety of inexpensive commercial products is now available to dampen drums in a more controlled manner. The most commonly used products consist of small adhesive pads that can be placed directly on the drumhead at desired locations, either singly or in combinations. An experimental investigation of the ringing drumhead modes and the effects of the damping pads is reported. Decay rate measurements indicate that the (3,1), (4,1), and (5,1) modes often contribute the most to the ringing sound, and that these modes are strongly affected by the damping pads. Another class of commercial dampener consists of thin annular rings of Mylar that conform to the perimeter of the drum head. These free-floating rings produce a similar damping effect, but dissipate energy through a different physical mechanism. Experimental results for both types of dampeners are presented and discussed in terms of viscoelastic and air-layer damping mechanisms, respectively.

In quantum field theory, a fundamental spin-12 particle can have intrinsic magnetic and electric dipole moments. Herein, we examine the way in which a charged fermion or photon is scattered by a massive neutral fermion via its dipole moment. In the low-energy limit, the field theoretic scattering amplitude can be related to a semi-classical electromagnetic interaction Hamiltonian. We find, in this limit, that the dipole field of the fundamental particle is that of a classical pure dipole, including the correct contact field. Additionally, we examine the optical properties of a medium consisting of magnetic dipoles. By computing the Compton scattering amplitude for a magnetic dipole, we find that a medium of polarized dipoles is circularly birefringent; that is, the index of refraction depends upon the polarization of the light. Our presentation is geared toward advanced undergraduate or beginning graduate students.

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