The sound of a leak
The sound of a leak

The “plinc, plinc” produced by the dripping of a tap or a leak in the ceiling is a recognizable sound and surely one of the most irritating to many, and of which there was no explanation of its origin until now.

Scientists from the University of Cambridge, led by Anurag Agarwal, director of the university’s acoustics laboratory, came up with a simple solution to eliminate noise.

A friend kept awake by a leak

Agarwal decided to investigate the sound of the drops after visiting a friend who had a leak in the ceiling.

THE NEXT DAY I SPOKE WITH MY FRIEND AND ANOTHER ACADEMIC, AND WE WERE ALL SURPRISED THAT NO ONE HAD ANSWERED THE QUESTION OF WHAT CAUSES THAT SOUND.

To investigate the origin, Agarwal designed an experiment with Peter Jordan, of the University of Poitiers, and the student of the engineering department Sam Phillips. All three used speed cameras, a microphone and a hydrophone to capture the sound of droplets falling into a water tank.

Air bubble

The research, published in the journal Scientific Reports, found that the sound produced by a drop of water hitting a liquid surface is not caused by it, but by the oscillation of a small bubble of air trapped under the surface of the water.

For the “plink” to be significant, the trapped air bubble must be near the bottom of the cavity caused by the impact of the fall. Then, the bubble drives the oscillations of the water surface in the lower part of the cavity, acting like a piston that drives sound waves in the air. This is a more efficient mechanism by which the underwater bubble drives the airborne sound field than previously suggested.

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The solution to the torment

For the “plinc” to be distinctive, the trapped air bubble must be near the bottom of the cavity.

Scientists say that to eliminate sound it is enough to change the surface tension of the liquid surface, for example, adding detergent or dishwashing soap.

Anurag Agarwal said the research could help find more efficient ways to measure precipitation or develop a synthetic sound of water droplets for video games and animations.

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