this is interesting. i wonder how/why inaudible sounds would affect people's moods. it's apparently called infrasound: "They showed the audience's emotions intensified as the inaudible sound vibrations, too low for the human ear to perceive, were blasted out during a 50-minute piano recital. Those feeling uncomfortable when the concert began, found their mood turning to anger. Others, who had felt happy, started to notice sensations of joy."