Pingpong Balls Make Bass Frequencies Vanish

Researchers at the University of Lille and the National Technical University of Athens have created a new acoustic "metasurface"; that is, a surface able to steer sound or electromagnetic waves in arbitrary directions. This one utilizes the humble ping pong ball.

Research paper here: https://publishing.aip.org/publications/latest-content/pingpong-balls-score-big-as-sound-absorbers/

The magic happens as a ping pong ball with a small hole punctured in it, turns into a "Helmholtz resonator"; think blowing across a glass bottle. Author Robine Sabat said of the discovery:

The Helmholtz resonator has the unique ability to capture ambient sound waves precisely at its natural frequency. Our motivation was to use these easily accessible objects to create a low-frequency insulating panel structure. Pingpong balls therefore present an economical alternative to acoustic insulators for both low cost and potential recycling.

The researchers started by coupling two such resonators together, and once successful, started to add more pingpong balls in a square sheet. This multiplied the number of different resonant frequencies that could be absorbed.

In adjusting the amount of balls and the sizes of the holes, the researchers could alter the properties of their cost-effective sound absorbing panel. Sabat added:

The potential of this metasurface extends beyond sound insulation. It can be broadened to achieve various functions similar to other metasurfaces. These functionalities encompass sound focusing, unconventional sound reflection, sound transmission manipulation, and more

For a primer on the Helmholtz Resonator principles, see this portion of a lecture by Dr. Andres Larraza to 2015 Monterey Academy of Oceanographic Science:

This isn't the first unique sound absorption method we've reported on this year. In August, we discussed a project  (Sonic TALK 767 )by the Bristol School of Biological Sciences, who used Moth wings as the inspiration for a new sound absorption solution.

Posted by MagicalSynthAdventure an expert in synthesis technology from last Century and Amiga enthusiast.