Voiced bilabial fricative
The voiced bilabial fricative is a type of consonantal sound, used in some spoken languages. The symbol in the International Phonetic Alphabet that represents this sound is ⟨β⟩, and the equivalent X-SAMPA symbol is B. The official symbol ⟨β⟩ is the Greek letter beta.
This letter is also often used to represent the bilabial approximant, though that is more precisely written with a lowering diacritic, that is ⟨β̞⟩. That sound may also be transcribed as an advanced labiodental approximant ⟨ʋ̟⟩, in which case the diacritic is again frequently omitted, since no contrast is likely. It has been proposed that either a turned ⟨β⟩, reversed ⟨β⟩ or affricate ⟨βθ⟩ can be used as a dedicated symbol for the bilabial approximant, but despite occasional usage none of them have gained general acceptance.
It is extremely rare for a language to make a phonemic contrast between the voiced bilabial fricative and the bilabial approximant. The Mapos Buang language of New Guinea contains this contrast. Its bilabial approximant is analyzed as filling a phonological gap in the labiovelar series of the consonant system rather than the bilabial series. Proto-Germanic and Proto-Italic are also reconstructed as having had this contrast, albeit with [β] being an allophone for another consonant in both cases. In Bashkir language, it is an intervocal allophone of /b/, and it is contrastive with /w/: балабыҙ [bɑɫɑˈβɯð] 'our child', балауыҙ [bɑɫɑˈwɯð] 'wax'.
The bilabial fricative is diachronically unstable (likely to be considerably varied between dialects of a language that makes use of it) and is likely to shift to [v].
The sound is not the primary realization of any sound in English dialects except for Chicano English, but it can be produced by approximating the normal English [v] between the lips; it can also sometimes occur as an allophone of /v/ after bilabial consonants.
Features
Features of the voiced bilabial fricative:
- Its manner of articulation is fricative, which means it is produced by constricting air flow through a narrow channel at the place of articulation, causing turbulence.
- Its place of articulation is bilabial, which means it is articulated with both lips.
- 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.
- Because the sound is not produced with airflow over the tongue, the central–lateral dichotomy does not apply.
- Its airstream mechanism is pulmonic, which means it is articulated by pushing air solely with the intercostal muscles and abdominal muscles, as in most sounds.