Mechanic of pubërphonia

Mechanism of frequency change by UMAR. Increase the weight and vibration of the uvula, initiate more action.

When the pharynx is open (or not constricted, like for swallowing), the vocal tract will be larger and the pitch of the air will be lower.

When the larynx is pulled down (as in yawning), the vocal tract becomes longer. This creates a lower pitch in the air (lower formant frequencies). 

When the jaw is more closed, the vocal tract is longer, has a more narrow opening, and the pitch of the air is lower (the pitch is lower)

The parts of the body that can vibrate in harmony with the voice are often called resonators." You can feel this by tilting your head back and saying, in a low voice, "Awwwww". Put a hand on your chest and feel it rumble. Now tilt your head forward, place a hand on your head, and say, "Heeeeeeeeeee" in a high voice. Feel the vibrations in your skull? In fact, the air column from the larynx to the lips functions very much like a uniform tube, without much variation in width.

You can feel this by tilting your head back and saying, in a low voice, "Awwwww". Put a hand on your chest and feel it rumble. Now tilt your head forward, place a hand on your head, and say, "Heeeeeeeeeee" in a high voice. Feel the vibrations in your skull?

The following is a list of resonators and the pitches or vocal qualities that most easily activate them.

Chest and Lower Body: low pitches and open sounds ("AW")

Throat - mid-range, easy speaking tone

Mouth - upper mid-range, mid-vowels

Nasal - close, front vowels, especially when followed by a nasal consonant.

Facial - high range, front vowels

Sinuses: given that there are so many sinuses, many different quality sounds activate them.

Bones of the skull - falsetto, very high range, closed vowels.

Does moving your hand help control your voice while speaking?

There’s not a lot of literature on this subject, but I think I can make a strong case that moving your hand (and other gestures often called "studioisms") are helpful for singing. Basically, this breaks down both consciously and unconsciously as follows:

Consciously, it can be a challenge to manifest a number of internal physical actions without the use of external body direction. The most common example of this is with airflow: lots of people will use a hand to mimic their airflow, which reminds them at all times where the air is going.

There’s also an unconscious component here, which is maybe more interesting and surprising: arm tension correlates to laryngeal tension. This is pretty easy to test for yourself, too: while singing a phrase, tense and relax your bicep and see how much easier it is to sing gently with your bicep released. It also works the opposite way: if you try to sing tensely with a loose arm, it’s actually pretty hard to do. When you do a studioism (immersive studio) properly, you’re preventing your arm from stiffening, which cuts down on laryngeal tension, though obviously not entirely. 

The following results are demonstrated in producing low pitch from high pitch. 1. The jaw and lip opening increase with rising pitch, presumably as a result of voice training. The opposite is what we do 2. The position of the tongue is characteristic of the vowel. More air flow we create. 3. The pharynx opening and aperture at the larynx vestibule are consistently narrow, and the narrowest larynx openings occur on the lowest and highest pitches. WE open the vocal cord 4. A progressive upward movement of the hyoid bone and longitudinal cartilages corresponds to the rising pitch. We lower the hyoid. This upward movement amounts to 18 mm. over the range of more than two octaves. We do it in the opposite direction. 5. The rising pitch results in a narrowing of the larynx ventricle vertically and a closer approximation of the ventricular bands to the vocal cords. We open the larynx.

These steps are difficult to understand and do. We do step-by-step workshops that anyone can follow and complete.