Possibility of turning waste heat Into electricity through sound

Actually this is simply setting up standing waves of hot air in small tubes - the pressure of which then impinges on piezo-electric material, thus creating electric current. IOW, use heat to create "trapped air motion" in an enclosed tube, then use piezo-electric crystals which have the very handy property of converting any applied deformations, into electricity. Maybe not groundbreaking physics, but still useful if it could be applied large-scale. I guess the challenge might be to find the best (optimal) coupling conditions between the resonant tube and the piezo material. What frequencies and amplitudes (or air pressures) will couple best with the properties of the piezo, for best efficiency? Acoustics geeks (and greenies) will want to know ...