When jelly gets the blues: Audible sound generation with gels and its origin

We report investigations concerning the mechanism for the audible sound generation of humming or ringing gels. As claimed earlier, the sound stems from the resonance of shear modes within the gel body. We present evidence for this claim by comparing the directly measured sound velocity, determined with a simple acoustic spectrometer, with the calculated one from measurements of the shear modulus and the mass density. Data were collected for different gel porosities. Deviations at comparatively small porosities are assumed as due to a frequency-dependent shear modulus.