A doubly articulated sound: the labiovelar approximant [w]

The labiovelar approximant [w] is closely related to the cardinal vowel [u]. Just as many phoneticians and phonologists treat [j] as the consonantal equivalent of [i], so they also treat [w] as the consonantal equivalent of [u].

For [w], there were two articulations with the same degree of stricture, and we say that [w] is a double articulation: open approximation at (1) the lips, (2) the tongue back at the velum. The tongue back is raised up to the soft palate (i.e. the velum) in a stricture of open approximation. At the same time, the lips are closely rounded, but not so close as to produce friction noise: in other words, there is a second stricture of open approximation, at the lips. The velum is raised, so air does not escape through the nose. The vocal folds are vibrating, so there is voicing.

The labiovelar approximant shares its articulatory features with cardinal vowel 8, [u]. Produce CV8 and hold it: [u:::]. Now make another vowel sound such as [ɑ:::], and alternate the two sounds. Gradually make the [u] sound shorter, until it is extremely short, and you will end up with something like [wɑ:::wɑ:::]. The labiovelar approximant can be thought of as a very short, non-syllabic version of [u].

If you look at the ‘approximants’ row on the IPA chart, you will see that there is no place for [w], unlike [j]. This is because [j] has only one constriction, which is the tongue body at the soft palate, so [j] appears in the column headed ‘palatal’. [w], as a doubly articulated sound, has two places of articulation, a circumstance that does not fit neatly on the IPA chart.