 This basic model was able to produce simple vowel sounds only, though some additional articulation was possible by positioning one's hand at the bell opening to obstruct airflow.The physical hardware for constructing the nasals, plosives and fricatives that most consonants require was not present, however.Kempelen, like many other early pioneers of phonetics, misunderstood the source of the perceived "higher frequencies" of certain sounds as a function of the glottis, rather than as the function of the formants of the entire vocal tract, so he abandoned his single-reed design for a multiple-reed approach.