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To be honest, it depends greatly, on both the voice and the masses he is trying to force into motion. There have been men and women in our history, who, through their skills in oration, or their intelligence, or their eloquence, have caused huge changes in the world with just their voice. Martin Luther King jr. could be considered a great example of this. Because his message was one of power, and because of the great leadership abilities he possessed, MLK jr. was able to move mountains with just the strength 0f his voice. And yet, his power and influence also greatly rested on his audience. The people he moved were people receptive to his claims, tired of one thing or many and ready to do something about it. In essence, one man cannot make an explosion: he can only light a fuse. There must be power, controversy, potential for change already inherent in his audience for his words to have any effect. If MLK spoke only to white individuals, or if the issues he attacked had not occurred, then he would have had zero followers no matter how gifted of a leader. Where the two elements combine- the powder keg and the person capable of lighting the fuse -  only there can an explosion occur.