The voiced labio-velar approximant is a type of consonantal sound, used in certain spokenlanguages, 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. In inventory charts of languages with other labialized velar consonants, /w/ will be placed in the same column as those consonants. When consonant charts have only labial and velar columns, /w/ may be placed in the velar column, (bi)labial column, or both. 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).
Landau, Ernestina; Lončarić, Mijo; Horga, Damir; Škarić, Ivo (1999), "Croatian", Handbook of the International Phonetic Association: A guide to the use of the International Phonetic Alphabet, Cambridge: Cambridge University Press, pp. 66–69, ISBN0-521-65236-7
Pukui, Mary Kawena; Elbert, Samuel H. (1986), Hawaiian Dictionary, Honolulu: University of Hawaiʻi Press, ISBN0-8248-0703-0
Rogers, Derek; d'Arcangeli, Luciana (2004), "Italian", Journal of the International Phonetic Association34 (1): 117–121, doi:10.1017/S0025100304001628
Šuštaršič, Rastislav; Komar, Smiljana; Petek, Bojan (1999), "Slovene", Handbook of the International Phonetic Association: A guide to the use of the International Phonetic Alphabet, Cambridge: Cambridge University Press, pp. 135–139, doi:10.1017/S0025100300004874, ISBN0-521-65236-7