Vowel /a/ is approximated by a combination of the narrow and wide tubes with about the same length. The following video shows when the lengths of the narrow and wide tubes are changed while the total length of the two tubes is kept the same.
- Arai, T. (2019). “Vocal-tract models in phonetic teaching and research,” Routledge Handbook of Phonetics, edited by Katz, W. F. and Assmann, P. F., Routledge, 570–598.