How do sperm whales vocalize? This is...apparently...a topic that LessWrong readers are interested in, and someone asked me to write a quick post on it.

The clicks they make originate from blowing air through "phonic lips" that look like this; picture is from this paper. This works basically like you closing your lips and blowing air through them. By blowing air between your lips with different amounts of tension and flow rate, you can vary the sound produced somewhat, and sperm whales can do the same thing but on a larger scale at higher pressure. As this convenient open-access paper notes:

Muscles appear capable of tensing and separating the solitary pair of phonic lips, which would control echolocation click frequencies. ... When pressurized air is forced between these opposing phonic lips, they vibrate at a frequency that may be governed by airflow rate, muscular tension on the lips, and/or the dimensions of the lips (Prestwich, 1994; Cranford et al., 1996, 2011).

After the phonic lips, sound passes through the vocal cap. The same paper notes:

The phonic lips are enveloped by the “vocal cap,” a morphologically complex, connective tissue structure unique to kogiids. Extensive facial muscles appear to control [...]

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Narrated by TYPE III AUDIO.

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Images from the article:

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