The Venturi Effect is a phenomenon described by Bernoulli’s equation, which states: when a fluid (air, water, anything that flows) is flowing through a pipe, and is forced through a narrower section of pipe, the pressure decreases while the velocity increases. In science, Bernoulli’s equation is for enclosed conduits but we will relate it to singing in the upper range.
Another way of stating the Venturi Effect is to say, that the amount of pressure exerted by a substance flowing through an opening will vary according to the inverse square of that opening. Confused? Think of a garden hose with water running. If you put your thumb over the opening and partially block it, the water reaches to a greater distance than when the opening is unblocked.
In singing the substance is air flow rather than water, and the opening is the glottis (vocal cord aperture). For singers, the greater distance reached by the water represents a higher note. The velocity is the rate of phonation (vibrations of the vocal cords), and as stated above, the pressure decreases.
All this is to say that, as you go up in your range, the pressure on the cords must decrease while the rate of phonation increases. This cannot be overstated. As indicated in previous sections, we know that as you go up in your range the vocal cords thin and lengthen. (To review this idea, please see The Vocal Cords).
The subglottal pressure decreases due to the increased firmness (or closing) of the cords. The increased rate of phonation combined with the smaller opening of the vocal cords needed for a high note permits less air to flow over the cords. Naturally, there is a feeling of holding back your breath; this is a good and necessary constriction in the throat related to proper note articulation. This also implies that, in order to sing a higher note, the glottal closure is more important than attempting to manipulate air pressure from the lungs to the cords.
Many singers feel they need to add pressure, use more air, push, or “go for it” in order to sing a high note but this is a misconception; by understanding the Venturi Effect we find that the opposite is actually true. The smallness or firmness of the glottis and less subglottal pressure is essential when attempting to singing in your upper range. High notes sound louder because they are higher and have natural projection, not because we attempt to sing them louder. In fact, we attempt to sing them softer, to decrease the pressure to the glottis, but they come out louder because they’re higher, which gives them natural projection.
We find, therefore, that less is more: most singers are afraid of high notes because they attempt to take too much weight into the upper range. You have to shed pounds as you go up. The cords can only adduct (come together) properly with less pressure to the glottis (see Light Attack). Subglottal pressure results in pushing. Singers push because they don’t understand this principle. It may sound a bit complicated, but its not really if you are properly guided through the process with appropriate vocal exercises. Most students are happily surprised to discover how easy it is to sing in their upper range with comfort and ease at any dynamic.
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Fluid Dynamics VII: The Venturi Effect