An harangue is a passionate and vehement speech, one that is usually lengthy and delivered before a public gathering: "The candidate indulged in an (or a) harangue that dealt more with his opponents than with the issues at hand." A tirade is a prolonged outburst of emotionally toned, vehement denunciation of some person or object. The distinctions between harangue and tirade are these: (1) A tirade is always an attack; an harangue may be only a long, violent speech. (2) An harangue is always made to an audience of some size; a tirade can be directed to or at one person only.
Dictionary of problem words and expressions. Harry Shaw. 1975.