What causes stronger explosions of air going into the glottis?
The longer the closed phase, the more the air pressure builds up — thus the stronger the explosion. With soft phonation the closed phase is proportionately short, and air pressure doesn’t get as much chance to build up. The explosion is weaker. With loud phonation, the closed phase is proportionately longer, and the air pressure builds up more. Therefore, the explosion is stronger. How does the closed phase get longer? The muscles in the larynx that bring the vocal folds together contract more strongly, squeezing the vocal folds together harder, so they can resist the air pressure longer. Those muscles are the thyroarytenoids, lateral cricoarytenoids, and interarytenoids. The muscles in the neck may also help provide stabilization, or may actually help produce the squeezing effect. What happens to the opening phase when more air pressure builds up? When the air pressure builds up for a longer time, not only does the air explode more strongly through the larynx, but the vocal folds are
