Often musical instruments have an air cavity. The cavity serves as a resonator, wherein sound waves bounce back-and-forth, and amplify. In many instruments, the resonating acoustic waves are allowed to escape from the cavity. In some instruments with a small opening, such as whistles and flutes, the resonance at the vent results in a large amplification of specific tones. This is known as Helmholtz resonance. When the vent size is large, such as the hole in soundboard of an acoustic guitar, a resonating monotone will simply leak at the opening, retaining the characteristics (wavelength and frequency) of the standing waves inside the cavity. We call this leaky resonance. Such leaky resonance can also be found, for instance, when seiche waves (notorious for causing flooding along lakes Michigan and Erie) from a partially-enclosed lake, leak into a connected water body. We reproduce such a system in our lab using water surface-waves, and highlight this aspect of leaky resonance in this video.
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