Curved-surface airflow, not the Bernoulli effect, drives lip vibration.

Evidence

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. To understand how airflow works on aircraft wings, yacht sails, vibrating lips or vocal folds, the thing to note is that they all have a curved surface, as illustrated for the piece of paper in front of the lips and the vocal folds on the left and right hand side of Figure 4.25, respectively. The air will move around the curve in a smooth curved streamline. We note earlier that (a) for a particle of air to change in direction, there must be a pressure difference across it (in this case, the curve in airflow direction is caused by a negative pressure gradient from atmospheric pressure toward the center of curvature) and (b) this pressure will reduce the closer the position is to the center of the curve, as indicated by the 3 minus signs of differing sizes in the figure. The smaller the minus sign the less pressure below atmospheric there is in that region. This means that the pressure at the surface of the curve must be lower than atmospheric pressure (as would be found well away from the surface where the airflow is not curved), which produces a force away from the center of curvature that can lift an aircraft’s wing, drive a yacht’s sail or lift the piece of paper (left side of Figure 4.25). — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1238

Categorization

• SEED: A common physics explanation for brass-instrument and wing lift gets corrected; angle: ‘why the Bernoulli explanation you learned is wrong’.
• XREF: connects to: Lip and vocal fold vibration is driven by Bernoulli pressure reduction from airflow — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1240; Lip oscillation sustains continuously while airflow and adduction persist — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1242