The resonance of the subglottis

Some vocal coaches say that, ”the resonance of the subglottis is important for vocalizing.”
When vocalizing, the voice is the sound, and the sound is the compression wave of air. The compression wave of air refers to the vibration and movement of air.
The vibration of air makes the eardrum vibrate in your ear. The brain recognizes this sound through the auditory nerve.
The action of exhalation, vibrates the vocal cords to make the vibration of air to be added the tone or resonance in the resonance chamber. Finally, it reaches to your eardrum as the voice.
However, the vibration of air is not made in the subglottis. This is because the subglottis is underneath the vocal cord, which it why it is not added the tone or resonance.
The subglottis deeply relates and affects exhalation. If the airflow is not stable in the subglottis it will impact the the vocal chords’ ability to vibrate. Therefor, If you take a breath correctly, you can vibrate the vocal chord effectively.