Bernoulli Effect

Term Category: Acoustics

The Bernoulli Effect, named after the Swiss mathematician Daniel Bernoulli, refers to a principle within fluid dynamics that states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or potential energy of the fluid. In other words, within a steady, incompressible flow of fluid, the total energy along a streamline (path that a fluid particle will follow) remains constant, which means that when a fluid (liquid or gas) increases in velocity, it must result in a reduction in the internal pressure or energy of the fluid.

This principle can be observed in various everyday phenomena. For instance, when you drink from a straw, the air pressure inside the straw decreases as you suck the air out, which is replaced by the liquid which is pushed up into the straw by the higher outside air pressure.

Impact on Singing

In the context of singing, the Bernoulli Effect plays a crucial role in how the vocal folds function to produce sound.

• Vocal Fold Vibration: When a singer exhales, the air from the lungs is pushed through the narrow space between the vocal folds, known as the glottis. According to the Bernoulli Effect, as the velocity of this airflow increases through the constricted glottis, the pressure drops. This drop in pressure creates a suction force that pulls the vocal folds towards each other, causing them to come together or adduct.
• Cycle of Vibration: After the vocal folds are brought together, the airflow briefly stops, causing the pressure below the vocal folds to build again. Once this subglottal pressure is sufficient to overcome the closure, the vocal folds are pushed apart, and the cycle repeats. This rapid opening and closing of the vocal folds—typically hundreds of times per second—sets the air particles above the vocal folds into vibration, producing sound.
• Pitch and Tone: The rate at which the vocal folds vibrate determines the pitch of the sound. Faster vibrations create higher pitches, while slower vibrations result in lower pitches. The Bernoulli Effect, in combination with the muscular adjustments made by the singer, helps to control these vibrations. Additionally, the way the vocal folds come together and apart—affected by the Bernoulli Effect—can influence the tone quality or timbre of the voice.