A vowel diagram or vowel chart is a schematic arrangement of vowels within a phonetic system. Vowels do not differ in place, manner, or voicing in the same way that consonants do. Instead, vowels are distinguished primarily based on their height (vertical position), backness (horizontal position), and roundedness (lip articulation). The degrees of height and backness may be used to describe either tongue articulation or acoustic quality, depending on the method of analysis. The former is the more traditional method, while the latter is the more modern method.
The vowel systems of all languages can be represented by vowel diagrams. Usually, there is a pattern of even distribution of vowel placement on the diagram, a phenomenon that is known as vowel dispersion. Most languages have a vowel system with three extreme points, forming a vowel triangle. Only 10% of languages, including English, have a vowel system with four extremes. Such a diagram is called a vowel quadrilateral or a vowel trapezium.[1]
Alternatively, these terms are used to distinguish the method of analysis used for vowel diagrams: vowel triangles for diagrams typically based on acoustics, and vowel quadrilaterals for diagrams typically based on articulation. As such, languages which have three extremes may still be plotted within a vowel quadrilateral, and languages which have four extremes may still be represented with a vowel triangle.
By articulation
The IPA vowel trapezium. Vowels in most languages are not so extreme, and fall somewhere within the chart rather than at its absolute bounds.
The vowel diagram of the International Phonetic Alphabet is based on the cardinal vowel system, displayed in the form of a trapezium. In the diagram, convenient reference points are provided for specifying tongue position. The position of the highest point of the arch of the tongue is considered to be the point of articulation of the vowel.[citation needed]
The vertical dimension denotes vowel height, with close vowels at the top and open vowels at the bottom of the diagram. For example, the vowel [i] is articulated with a close (high) tongue position, while the vowel [a] is articulated with an open (low) tongue position.
The horizontal dimension denotes vowel backness, with front vowels on the left and back vowels on the right of the diagram. For example, the vowel [i] is articulated with the tongue further forward, while the vowel [u] is articulated with the tongue further back.
Vowels are categorized by their roundedness, either rounded or unrounded. For example, the vowel [u] is articulated with rounded lips, while the vowel [i] is articulated with spread lips. For positions on the diagram where both rounded and unrounded vowels exist, rounded vowels are placed right adjacent to their unrounded counterparts.
A vowel chart for southern California English, showing how its vowels lie within the IPA vowel trapezium.
By definition, no vowel sound can be plotted outside of the IPA trapezium because its four corners represent the extreme points of articulation. The vowel diagrams of most real languages are not so extreme. In English, for example, high vowels are articulated lower than in the IPA trapezium, and front vowels are articulated further back.[1][3]
Vowels may also be categorized by their perceived tenseness, with lax vowels being positioned more centralized on vowel diagrams than their tense counterparts. The vowel [ə] is in the center of the IPA trapezium and is frequently referred to as the neutral vowel, due to its fully lax articulation. In many languages, including English, the vowels [ɪ] and [ʊ] are often considered lax variants of their tense counterparts [i] and [u], and are placed more centralized in the IPA trapezium.
By acoustics
A schematic vowel triangle arranged according to formants.
Different vowels vary in pitch. For example, high vowels, such as [i] and [u], tend to have a higher fundamental frequency than low vowels, such as [a]. Vowels are distinct from one another by their acoustic form or spectral properties. Spectral properties are the speech sound's fundamental frequency and its formants.
A plot of the average formants of a male speaker.
Each vowel in the vowel diagram has a unique first and second formant, or F1 and F2. 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. [i], [u], [a] are often referred to as point vowels because they represent the most extreme F1 and F2 frequencies. [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 higher for [i] because the oral cavity is short and the tongue is at the front of the mouth. 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.[4]
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).
12Paul Skandera and Peter Burleigh (2005). A Manual of English Phonetics and Phonology. Gunter Narr Verlag. pp.33–34. ISBN3823361252.
↑Ladefoged, Peter (1999). "American English". Handbook of the International Phonetic Association. Cambridge: Cambridge University Press. pp.41–44. ISBN0-521-63751-1.
↑Heinz J. Giegerich (1992). English Phonology: An Introduction. Cambridge University Press. pp.14–15. ISBN0521336031.
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