The Journal of the Acoustical Society of America · 1989 · 199 citations · 0 references
Natural SciencesPhysicsAcousticsOcean AcousticsUnderwater AcousticsAcoustic MeasurementNoiseUnderwater Sound PropagationExperimental AcousticsHydrodynamic NoiseRain NoiseRaindrop ImpactRaindrop Size DistributionSurface Tension ContributionsSurface Tension WavesUnderwater Noise
The 14–16 kHz spectral peaks have been observed in real rain measurements. The study experimentally investigates the underwater sound generated by water drop impacts on the surface. The authors describe conditions under which each drop impact generates a bubble, which are likely met by many raindrops in a typical shower. The study shows that underwater sound arises from both the initial impact and bubble formation, that bubble‑induced peaks at 14–16 kHz are present in real and artificial rain but disappear when surface‑tension‑reducing liquids are added, and that these peaks are consistent with bubble‑ringing theory.
An experimental study of the underwater sound produced by water drop impacts on the surface is described. It is found that sound may be produced in two ways: first when the drop strikes the surface and, second, when a bubble is created in the water. The first process occurs for every drop; the second occurs for some impacts but not others. A range of conditions is described in which a bubble is produced for every drop impact, and it is shown that these conditions are likely to be met by a significant fraction of the raindrops in a typical shower. Underwater sound produced by artificial as well as real rain is reported. A comparison between artificial and real rain noise power spectra shows some deviations due to different drop-size distributions. Addition of surface tension reducing liquids to the water in the test tank caused a disappearance of the characteristic spectral peaks in the frequency range 14–16 kHz. These peaks have been observed by several scientists during measurements of real rain. Our findings provide evidence for the theory that the 14- to 16-kHz spectral peak is caused by the ringing of bubbles entrained in the water by the drop impact process.