Institute of Systematic Musicology
Acoustic metamaterials are complex geometries leading to acoustic behavior not found in natural material, like negative stiffness or refraction, cloaking or spectral bandgaps. Indeed musical instruments are complex structures and some may already qualify as metamaterials. Still altering the instrument geometries and adding metamaterial behavior can increase the instruments sound variability and articulatory possibilities or lead to sounds not expected from mechanical instruments at all. The paper presents such examples. When modifying a frame drum by adding additional point masses forming a ring, the frame drum shows cloaking behavior when struck in the middle of the ring, where frequencies within a certain frequency band cannot leave the ring. This leads to a bandgap in the spectrum in the mid frequency range. Still when striking the drum outside the ring a normal drum sound is achieved. Therefore a drummer can produce sounds not known from drums before while with the same instrument can also play regular sounds. Other examples are modified guitar top plates with added point masses or waveguide structures.
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