Vowel diagram

[2] Vowels are unique in that their main features do not contain differences in voicing, manner, or place (articulators).

[3] In the vowel diagram, convenient reference points are provided for specifying tongue position.

The schwa [ə] is in the center of the chart and is frequently referred to as the neutral vowel.

The frequency of the first formant refers to the width of the pharyngeal cavity and the position of the tongue on a vertical axis and ranges from open to close.

The frequency of the second formant refers to the length of the oral cavity and the position of the tongue on a horizontal axis.

[a] has a high F1 frequency because of the narrow size of the pharynx and the low position of the tongue.

The F2 frequency is low in the production of [u] because the mouth is elongated and the lips are rounded while the pharynx is lowered.

By definition, no vowel sound can be plotted outside of the IPA trapezium because its four corners represent the extreme points of articulation.

[2][6] Legend: unrounded • rounded The official vowel chart of the International Phonetic Alphabet does not include vowel symbols with added diacritics as shown here, and only gives labels for the heights "close", "close-mid", "open-mid", and "open" (shown here in bold).