The science of humming

The vocal cord is vibrating when humming.
I’ve observed the vocal cord vibrating when a singer is humming precisely.
The process of humming is the action of when closing your mouth, the air and sound waves travel to go through the nasal cavity. The sound then vibrates in the soft palate and the nasal cavity.
Note:The sound is made by vibrating air, which cannot make a sound without an exit for the sound.
So, even if you close your mouth, the air goes out through the nose. If you close both mouth and nose, you cannot make the sound.
In the case of humming, the sound is made by using nasal cavity, which consists of (1) a narrowed resonance chamber (2)lengthening the resonance chamber (3)a decrease in exhaled air.