Designing Musical Instruments and Room Acoustics with Acoustic Metamaterials

Mechanical musical instruments have less timbre variability than electronic instruments. Extended playing techniques and more sophisticated acoustic instrument designs have recently appeared. We suggest acoustic metamaterials as a new way to extend the timbre of mechanical instruments beyond their present sound capabilities. In this chapter, we present three examples of acoustic metamaterials: (1) a one-dimensional string, (2) a labyrinth sphere, and (3) a two-dimensional membrane. The string is covered with additional masses, which leads to a dispersion relation of the harmonic overtones in the sound spectrum. The resulting sound still has a detectable pitch but is very different from a regular string on a mechanical instrument. The labyrinth sphere has a clear band-gap damping and can be used in loudspeakers, musical instruments, or room acoustics due to its small size. A circle of masses is attached to the membrane, leading to a cloaking behaviour of vibrations from within the circle to outside and vice versa. Again, the resulting sound is considerably different from a regular drum and leads to increased variability of musical articulations. Using a microphone array, laser interferometry, impedance tube, and high-speed video recordings with subpixel tracking, the vibrations on the string and the membrane are investigated and discussed in relation to new instrument designs.