Close central rounded vowel
The close central protruded vowel is typically transcribed in IPA simply as, and that is the convention used in this article. As there is no dedicated diacritic for protrusion in the IPA, symbol for the close central rounded vowel with an old diacritic for labialization,, can be used as an ad hoc symbol for the close central protruded vowel. Another possible transcription is or, but this could be misread as a diphthong.
Occurrence
Because central rounded vowels are assumed to have protrusion, and few descriptions cover the distinction, some of the following may actually have compression.
As there is no official diacritic for compression in the IPA, the centering diacritic may be used with the front rounded vowel, which is normally compressed, to create the ad hoc symbol. Other possible transcriptions are and .
Occurrence
This vowel is typically transcribed in IPA with. It occurs in some dialects of Swedish, but see also Close front [rounded vowel#Close front compressed vowel|close front compressed vowel]. The close back vowels of Norwegian and Swedish are also compressed. See close back compressed vowel. It also occurs in Japanese as an allophone. Medumba has a compressed central vowel where the corners of the mouth are not drawn together.
Near-close central rounded vowel
Some languages feature the near-close central rounded vowel, which is slightly lower. It is most often transcribed in IPA with, and, but is also a possible transcription. The symbol, a conflation of and, is used as an unofficial extension of the IPA to represent this sound by a number of publications, such as Accents of English by John C. Wells. In the third edition of the Oxford English Dictionary, represents free variation between and.
Near-close central compressed vowel
As there is no official diacritic for compression in the IPA, the centering diacritic may be used with the front rounded vowel, which is normally compressed, to create the ad hoc symbol. Other possible transcriptions are and .