bilabialfricative

A bilabial fricative is a consonant sound produced by constricting the airflow at the lips (bilabial) to create continuous friction noise, rather than a complete stop. The term encompasses both voiceless and voiced variants, depending on whether the vocal cords vibrate during articulation.

In the International Phonetic Alphabet, the standard symbols for the two main bilabial fricatives are [ɸ] for the voiceless form and [β] for the voiced form. Some languages realize these segments as more open approximants rather than true fricatives, and transcription can reflect such variation. The exact articulation can vary by language, with perceptual differences in how sharp or noisy the frication sounds.

Bilabial fricatives are relatively rare cross-linguistically and may occur as phonemic segments or as allophones of other bilabial sounds under certain phonological or phonetic conditions. They often contrast with bilabial stops like [p] and [b], or with labiodental fricatives like [f] and [v], highlighting a distinct place of articulation at the lips.

A well-known example in scholarly discussion is the Japanese phonetic realization of the syllable "fu," which is commonly described as involving a voiceless bilabial fricative [ɸ] combined with a following vowel. This illustrates how bilabial fricatives can appear in combination with vowels and influence neighboring articulations.

See also: bilabial stop, labiodental fricative, bilabial approximant.