Researchers describe an acoustic meta-surface that uses pingpong balls, with small holes punctured in each, as Helmholtz resonators to create inexpensive but effective low-frequency sound insulation. The coupling between two resonators led to two resonance frequencies, and more resonant frequencies meant the device was able to absorb more sound. At the success of two coupled resonators, the researchers added more, until their device resembled a square sheet of punctured pingpong balls, multiplying the number of resonant frequencies that could be absorbed.
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Source: ScienceDaily