Does sound gets faster when air bubble is suspend in water?

c = sqrt(K/P)

c = speed

K = bulk module

P = density

When air bubbles is homogenized into water the density is lower, so should sound gets faster? Thank you.

  • $\begingroup$ don't forget that $K=P\frac{dPr}{dP}$ where $Pr$ is pressure, so your equation becomes $c=\sqrt{\frac{dPr}{dP}}$ $\endgroup$ – Jim Apr 22 '14 at 13:46
  • $\begingroup$ What do you think? Have you tried something to calculate the speed of sound through a particular concentration of bubbles in air? $\endgroup$ – user31782 Apr 22 '14 at 14:34
  • $\begingroup$ Please clarify: do you want the speed of sound thru a macroscopic airbubble embedded in water, or the change of speed of sound in water full of dissolved air vs. pure water? $\endgroup$ – Carl Witthoft Apr 22 '14 at 17:02
  • $\begingroup$ I am comparing between sound travelling through macroscopic air bubble in water and without air bubble. $\endgroup$ – Kevin Apr 23 '14 at 15:47

For many small bubbles in water distributed homogeneously, as in the hot chocolate effect, the speed of sound decreases because the density only decreases slightly while the bulk modulus decreases dramatically (because most of the squeezing is done on the air in the bubbles, not the water). By "small" I mean small as compared to the wavelength of the sound. For audible sound this can be as small as 1 cm for 34kHz, and since most bubbles will be this size or less, then the reasoning above should be valid. (For something nonhomogeneous, like a single bubble in a container of water much longer than the sound wavelength, then we'd have the speed of sound be slower near the bubble and faster away from it.)

The mathematical details are listed here (behind paywall): http://dx.doi.org/10.1119/1.13080

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  • $\begingroup$ Could part of the effect be due to the scattering of the waves through the inhomogeneities? The bubbles are smaller than the wavelength, but they can still produce some interaction that may retard them. (I haven't read the article, I don't have access). $\endgroup$ – Davidmh Jun 11 '14 at 0:57

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