This method is less efficient due to more energy losses
taking place while conversion of sound energy to heat
energy and then heat energy to electric energy then the other
methods. As here the conversion is done two times .you may
think that according to Newtown’s law energy can’t be
created nor destroyed it could be only converted from one
form to another .So while converting sound energy to heat
energy there will be some loss of sound energy as some of
the sound energy would be converted into another form also
while converting from heat energy to electric energy all
energy wouldn’t be converted into electric energy some of
the heat energy would get converted into another form of
energy. And here as our main focus is to convert sound
energy to electric energy so conversion into other form of
energy is loss of energy for us