Students of language have in general placed primary emphasis upon the generating mechanisms of speech. For example, it is common to classify the sounds of speech in physiological terms; phonetic tables and charts usually show organic position or mechanism in one dimension and method of production in the other. There has also been considerable interest in the acoustical effects or results of speech production. Von Kempelen was among the first to promote a serious interest in this subject, with a volume published in 1791. The literature on the subject is far more distinguished and extensive than most linguists realize; but it cannot compare with the much more voluminous literature on physiological phonetics and voice production. Within the past ten years, great impetus has been given to the study of acoustic phonetics by developments in electro-acoustical instrumentation and by the new, important, and challenging problems which have come upon the field of communication engineering.