A voiceless bilabial implosive is a rare consonantal sound, used in some spoken languages. The symbol in the International Phonetic Alphabet that represents this sound is ⟨ɓ̥⟩ or ⟨pʼ↓⟩. A dedicated IPA letter, ⟨ƥ⟩, was withdrawn in 1993.
Features of the voiced bilabial implosive:
Its manner of articulation is occlusive, which means it is produced by obstructing airflow in the vocal tract. Since the consonant is also oral, with no nasal outlet, the airflow is blocked entirely, and the consonant is a stop.
Its place of articulation is bilabial, which means it is articulated with both lips.
Its phonation is voiceless, which means it is produced without vibrations of the vocal cords.
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.
The airstream mechanism is implosive (glottalic ingressive), which means it is produced by pulling air in by pumping the glottis downward. As it is voiceless, the glottis is completely closed, and there is no pulmonic airstream at all.
A rare and evidently unstable sound, /ɓ̥/ is found in Bernese German, the Serer of Senegal, the Owere dialect of Igbo in Nigeria, and in some dialects of the Poqomchi’ and Quiche languages of Guatemala. Owere Igbo has a seven-way contrast among bilabial stops, /pʰ p ƥ bʱ b ɓ m/, where [ƥ] is allophone of [k͡p] and [ɓ] is allophone of [ɡ͡b].
