The Bernoulli effect is a wrong explanation for vocal fold vibration
Evidence
Soon after they are momentarily shut, the folds are forced open again by air pressure and flow from the lungs. As they are blown open, the folds acquire some velocity and momentum, causing them to continue to open, but like an oscillator, they resist stretching with an opposing tension. They reach a maximum opening and stretch, but the ensuing elastic rebound causes them to close, and the cycle then repeats. It is often stated that the Bernoulli effect (pressure is lower where air is flowing faster, as it is when it passes by the folds) is responsible for their closing, but this only part of the effect, probably more important for soft singing. The role of the elasticity and acquired momentum of the membranes (that is, the oscillator characteristics) involved should not be overlooked. Like an oscillator, the folds under a given tension and held at a given separation have a resonance frequency, which becomes the drive frequency for the vocal tract. For conversation, this drive frequency averages 100 to 125 Hz for males and 210 Hz for females; children average over 300 Hz. — Eric J. Heller, Why You Hear What You Hear- An…, 1661
The Bernoulli effect was used to explain the origin of this energy input to the system to cause the lips (or vocal folds) to move toward each other, but it turns out to be specious. Babinski (2003) gives an explanation that is based on considering air as being made up of very small particles that will be displaced if there is a pressure difference across them, and the movement will be toward the low-pressure side. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1238
The vibration of the vocal folds during speech or singing is commonly described with reference to the Bernoulli effect (including in the fourth edition of this book and by many other authors). It turns out that this is not appropriate as a physical explanation of vocal fold vibration, lift on aircraft wings or drive from a yacht’s sail. A more relevant explanation relates to pressure changes as air curves around obstacles, and this is described in Section 4.3.7 in the context of the vibrating lips of a brass player, since the explanation is exactly the same as for the vibration of the vocal folds (and brass instruments appear earliest in this book!). — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1325
Categorization
- XREF: Counterintuitive correction of the common Bernoulli explanation; connects to the trumpet feedback contrast later in the chapter. — connects to: Elastic recoil and momentum, not Bernoulli effect, mainly close the vocal folds; A sinusoidal vocal fold wave would make speech impossible; Bernoulli’s airflow across curved lips initiates their vibration (+4 more)
- DEEPTHINKING: Tightly packed mechanism: elasticity, momentum, oscillator resonance, and drive frequency for the vocal tract all in one paragraph. Rich enough to sit with.
- QUESTION: What precisely is specious about the Bernoulli account of self-sustained lip/fold oscillation, and how does Babinski’s pressure-gradient model differ in observable prediction?
- SEED: Angle: which commonly taught ‘pop science’ explanations in acoustics (and beyond) are quietly wrong, and why they persist across textbook editions.
- corroborated: 4 independent passages support this claim — Eric J. Heller, Why You Hear What You Hear- An…, 1661; David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1238; David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1325