Vocalizing during a whistle reveals that the whistle matches the second formant

Evidence

To check that the second formant is responsible for the whistling frequency, the formants and whistle frequency can be measured together. The trick is to start a lip whistle and then vocalize during the whistle without changing the shape of the vocal tract or lips. A weaker whistle may be heard when vocalizing. Record both a pure whistle and a vocalized whistle, and make a sonogram of the result. You may want to try whispering while whistling, providing a broadband white noise source that also lights up the formants. Or, without changing anything else, vocalize a croaking sound after whistling. — Eric J. Heller, Why You Hear What You Hear- An…, 1330

Categorization

• SEED: The self-experiment protocol (whistle, then vocalize without changing mouth shape, sonogram it) is a lovely citizen-science piece — could be framed as ‘how to hear your own formants’.
• CANDY: Whispering while whistling lights up formants on a sonogram — a fun kitchen-table experiment anyone can try.