Indian grammarians, 7th century, say vowels come in three distinct types:

palatal (“mouth vowels”) labio-velar (“lip vowels”) pharyngeal (“throat vowels”)

Each type is categorically distinct.

Within each type, jaw height may be used to distinguish vowels.

By the 19th century, further differentiation of constriction types was acknowledged, by allowing the lip and tongue actions to “mix.”

Continuous Vowel Space Theories

Bell invented central (“mixed’) vowels (around 1867).

Jones, 1956

IPA vowel trapezium

IPA pulmonic consonant chart with audio

chasquidos consonanticos, curiosidades…

alfabeto chino internacional. Inverted pyramid…

more about IPA paradoxes.

An interesting and significant story was once told by Carl Voegelin during a symposium held in New York in 1952 on the present state of anthropology. He told how, at the beginning of the 1930s, he was being taught phonetics by, as he put it, a “pleasant Dane”, who made him use the IPA symbol for sh in ship, among others. Some while later he used those symbols in some work on an American Indian language he had done for Sapir. When Sapir saw the work he “simply blew up”, Voegelin said, and demanded that in future Voegelin should use ‘s wedge’ (as š was called), instead of the IPA symbol.

AFA, Alfabeto fonético americanista

Desarrollado originalmente por americanistas, antropólgos y lingüistas europeos y norteamericanos para proporcionar una transcripción fiel de las lenguas indígenas de América que, por lo general carecían de una ortografía establecida.

Problem with equating vowel quality with resonances: head size