The voiced labio-velar approximant is a type of consonantal sound, used in certain spoken languages, including English. It is the sound denoted by the letter ⟨w⟩ in the English alphabet; likewise, the symbol in the International Phonetic Alphabet that represents this sound is ⟨w⟩, and the equivalent X-SAMPA symbol is w. In most languages it is a labialized velar approximant [ɰʷ], and the semivocalic counterpart of the close back rounded vowel [u] - i.e. the non-syllabic close back rounded vowel. As labio-velar consonants do not easily fit into consonant charts with only labial and velar columns, [w] may be put in either the velar column, (bi)labial column, or both, though putting it in both columns is rare; the placement may have more to do with phonological criteria than phonetic ones.
Features of the voiced labialized velar approximant:
- Its manner of articulation is approximant, which means it is produced by narrowing the vocal tract at the place of articulation, but not enough to produce a turbulent airstream. The type of approximant is glide or semivowel. The term glide emphasizes the characteristic of movement (or 'glide') of /w/ from the /u/ vowel position to a following vowel position. The term semivowel emphasizes that, although the sound is vocalic in nature, it is not 'syllabic' (it does not form the nucleus of a syllable).
- Its place of articulation is labialized velar, which means it is articulated with the back part of the tongue raised toward the soft palate (the velum) while rounding the lips. Some languages, such as Japanese and perhaps the Northern Iroquoian languages, have a sound typically transcribed as [w] where the lips are compressed (or at least not rounded), which is a true labial–velar (as opposed to labialized velar) consonant. Close transcriptions may avoid the symbol [w] in such cases, or may use the under-rounding diacritic, [w̜].
- Its phonation is voiced, which means the vocal cords vibrate during the articulation.
- It is an oral consonant, which means air is allowed to escape through the mouth only.
- It is a central consonant, which means it is produced by directing the airstream along the center of the tongue, rather than to the sides.
- The airstream mechanism is pulmonic, which means it is articulated by pushing air solely with the lungs and diaphragm, as in most sounds.
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