Whispering replaces vibrating vocal folds with jet turbulence as the sound source

Evidence

Whispering depends on jet turbulence noise produced by constricting the vocal folds so as not to vibrate as air is forced through them. The turbulence noise becomes the sound source for the vocal tract and lips. Resonant enhancement of certain frequency ranges (called formants; see chapter 17) controllable with vocal tract shape creates easily understood vowel sounds, just as with the usual vibrating vocal fold vocalization—in other words, same resonant tube, different sound source. — Eric J. Heller, Why You Hear What You Hear- An…, 1343

Categorization

• DEFINE: Clarifies that whispered vowels still carry formants because the resonant tube, not the source, shapes them.
• XREF: The ‘same resonant tube, different source’ framing connects to the reader’s interest in how source and filter separate. — connects to: Turbulent airflow produces the nonpitched noise sounds of speech like sh and ss. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1140; Lip and vocal fold vibration is driven by Bernoulli pressure reduction from airflow — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1240