What is the corresponding frequency of AC that is generated in bones due to their piezoelectric properties when is applied acoustic pressure in the frequency range of human voice for instance ?

The frequency of any generated voltage would, I assume, be the same as the applied stimulus.

 

Although it looks like bone is only piezoelectric (if it is) at kilohertz frequencies: http://silver.neep.wisc.edu/~lakes/BoneElectr.html

Same frequency as the strain, I assume too, especially for such a small effect.

 

The link doesn't suggest a reason for the cutoff frequency, but

- conductivity of moist or water is expected

- Water might also dissolve some piezo salts