However, some languages, such as French, German and Icelandic, distinguish rounded and unrounded front vowels of the same height (degree of openness), and Vietnamese distinguishes rounded and unrounded back vowels of the same height.
In Southern Teke, the sole language reported to have a phonemic /ɱ/, the labiodental sound is "accompanied by strong protrusion of both lips",[11] whereas the [ɱ] found as an allophone of /m/ before /f, v/ in languages such as English is not protruded, as the lip contacts the teeth along its upper or outer edge.
Also, in at least one account of speech acquisition, a child's pronunciation of clown involves a lateral [f] with the upper teeth contacting the upper-outer edge of the lip, but in crown, a non-lateral [f] is pronounced with the teeth contacting the inner surface of the protruded lower lip.
The lip position of unrounded vowels may be classified into two groups: spread and neutral.
For example, in Standard Chinese, the vowel /ɔ/ is pronounced [u̯ɔ] after labial consonants,[citation needed] an allophonic effect that is so important that it is encoded in pinyin transliteration: alveolar /tu̯ɔ˥/ [twó] (多; duō) 'many' vs. labial /pu̯ɔ˥/ [pwó] (波; bō) 'wave'.
In Vietnamese, the opposite assimilation takes place: velar codas /k/ and /ŋ/ are pronounced as labialized [kʷ] and [ŋʷ] or even labial-velar [kp] and [ŋm], after the rounded vowels /u/ and /o/.
[citation needed] A few ancient Indo-European languages like Latin had labiovelar consonants.
Contrasts based on roundedness are rarely categorical in English and they may be enhanced by additional differences in height, backness or diphthongization.
The vowels are open-mid [ʌ, ɔ] in the former dialect and open [ɑ, ɒ] in the latter.
In addition, LOT may be longer than STRUT due to its being a free vowel: [ɒː].
If THOUGHT is distinct, it is realized as [ɔ], whereas LOT is lowered to [ɒ] or raised to [o̞].
This means that while nought [nɔʔ] contrasts with nut [nʌʔ] by rounding, not may have a different vowel [nɒʔ ~ no̞ʔ].
[24] The potential contrast between the close-mid [øː] and the open-mid [œː] is hard to perceive by outsiders, making utterances such as the total onslaught [ðə ˈtœːtl̩ ˈɒnsloːt] sound almost like the turtle onslaught [ðə ˈtøːtl̩ ˈɒnsloːt].