Vocalization with semi-occluded airways is favorable for optimizing sound production.

Vocalization in mammals, birds, reptiles, and amphibians occurs with airways that have wide openings to free-space for efficient sound radiations, but sound is also produced with occluded or semi-occluded airways that have small openings to free-space. It is hypothesized that pressures produced inside the airway with semi-occluded vocalizations have an overall widening effect on the airway. This overall widening then provides more opportunity to produce wide-narrow contrasts along the airway for variation in sound quality and loudness. For human vocalization described here, special emphasis is placed on the epilaryngeal airway, which can be adjusted for optimal aerodynamic power transfer and for optimal acoustic source-airway interaction. The methodology is three-fold, (1) geometric measurement of airway dimensions from CT scans, (2) aerodynamic and acoustic impedance calculation of the airways, and (3) simulation of acoustic signals with a self-oscillating computational model of the sound source and wave propagation. Author summary: Humans and animals communicate vocally. For mammals, birds, and reptiles that breathe with lungs, a source of sound is embedded in the airways, somewhere between the lungs and the lips or beak. When the mouth or beak is open, sound radiates into free-space to be received by listeners. The wider the opening, the more sound is released from the airway. However, for centuries those who teach efficient voice production have encouraged their clients to practice with a nearly closed mouth, therefore partially occluding the airway. In the animal world, doves, frogs, and gerbils vocalize with completely closed airways, allowing the sound to radiate from vibrating skin surfaces instead of airway openings. It is shown here that by keeping most of the sound inside the body and widening the throat by vocalizing into a narrow tube at the mouth, the sound source can become more efficient. By controlling the airspace in the larynx directly above the vocal cords, an area known as the epilaryngeal airway, this efficiency can be maintained when the mouth is opened after practice. A large variety of sound qualities and a louder voice are thereby facilitated without a significant effect on vowel production. [ABSTRACT FROM AUTHOR]