Nothing can convert sound energy into heat energy.We know that sound is produced by vibrations.When a person speaks, the air closer to the mouth ispushed in the direction of the sound.As a result, the molecules in this layer of air get disturbed and start vibrating about their mean positions.These vibrations increases the kinetic energy among the molecules and produces heat.Thus heat is produced like this. it is not converted by any device. However,Sound energy may be converted into electrical energy for transmission, and later the electrical energy can be converted back into sound energy at the receiving end. An example of such transformations could be seen in the microphone and the loudspeaker.