Abstract
Gist [Phys. Rev. B 39 (to be published)] has argued that the frequency dependence of the ultrasonic attenuation which we measured in a liquid-helium-filled porous ceramic sample can be completely explained by the Biot theory of porous media acoustics. We find that when the measured values of the permeability and pore tortuousity are used in the calculations, there remain substantial discrepancies between the Biot theory and our experimental results, particularly for the pressure and frequency dependence of the attenuation. These indicate that in the crossover region between low- and high-frequency behavior it is necessary to consider the effects of a range of length scales in our sample.
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