Sound is just Longitudinal vibrations of air that are detected from objects like the ear. Hence it originates from a vibrator. For humans this vibrator is in the neck in the form of a vocal cord. So sound from humans really comes from the neck and the vibrations of air ascend up the neck and comes out from our mouth and nose. The question is I am able to hear someone's voice even if I am right behind them. Does this occur because of the diffraction of sound which is a wave as it passes through that person's nose and mouth? What is the difference in intensity of sound between someone standing 1m in front and 1m behind a person producing sound? Another question is sound waves interfere just like any other wave but when minima occurs, the sound dosen't neccessairly cancel (i.e. you would still hear some sound? Whereas light would, ie. dark fringes.