What is vocal cord closure, and how do I train it?
Vocal cord closure is how completely your vocal folds meet each time they vibrate. When they close well, all of the air turns into sound, and the tone is clear and carries without effort. When they leave a gap, air leaks out, the tone sounds breathy and you run out of breath early in a phrase. Squeezing them together too hard is the opposite fault and makes the voice sound pressed. A simple check is to hold a hiss on "s" and then a buzz on "z" for as long as you can: if the "z" runs out much sooner, air is escaping through the folds. Closure is trained with short, gentle exercises: sliding up from a quiet vocal fry onto a note, light staccato "uh-uh-uh" onsets, humming, and singing through a straw. Practise them quietly. More volume does not mean better closure.