Despite of the the remarks concerning the perceptual formant integration and some other factors, it is assumed that an F1/F2-plot based on Bark-scale, in which the vowel points can be plotted according to a continuous scale, is capable to show in the most cases the psycho-acoustical vowel differences concerning the features front/hack, close/open, and rounded/ unrounded (with some consideration also tense/lax). About 5 0 vowel symbols have been used for the description of the vowel systems of the world. About the same number of 1 Bark sized circles have room on the physiologically possible F1/F2-space, This number seems to be near the general F1/F2 vowel resolution. Different scales of the F1/F2-plot for the psycho-acoustical simulation, exemplified by German vowel material, are compared with each other: full logarithmic (A), linear up to 510 Hz, logarithmic above 510 Hz (B); technical mel-scale (C), F1/F2- plot (D).
Bibliographic reference. Iivonen, Antti / Toivonen, Raima (1989): "Simulation of the psycho-acoustical vowel space for linguistic applications", In EUROSPEECH-1989, 2289-2292.