Almost every boy experiences vocal changes as they go through puberty and the growth of the vocal cords will cause his voice to change unexpectedly. For a while, your son might have difficulty controlling it and he will make all sorts of odd noises when trying to speak.
The 'noise' is caused by his larynx (or voice box) as it grows larger and thicker. This change happens in both boys and girls, but the adjustment is more evident in boys. Girls' voices only deepen by a couple of tones and the change is barely noticeable. Boys' voices on the other hand become significantly deeper.
The larynx, which is located in the throat, plays the major role in creating the sound of the voice. Two muscles, or vocal cords, are stretched across the larynx and they are kind of like rubber bands.
Before a boy reaches puberty, his larynx is small and his vocal cords are small and thin too. That is why his voice is higher than an adult's is. However, as he goes through puberty, the larynx grows and his voice gets deeper. Along with the larynx, the facial bones begin to grow, too. Cavities in the sinuses, the nose and at the back of the throat grow larger thus creating more space for the voice to resonate.
As a boy's body adjusts to this changing physiology, his voice may crack or break frequently. This process lasts only a few months and when the larynx has finished growing, your son's voice will not make any unpredictable sounds.
Everyone's timetable is different. As a ballpark, a boy's voice typically begins to change between ages 11 and 14, usually just after the major growth spurt. Some boys' voices might change gradually, whereas others' might change quickly.
Voice change is normal, and there is a chance your son may not even realise that his voice is gradually deepening and lowering. However, he may be embarrassed when his voice cracks or squeaks in front of others. He should know that these cracks are only temporary, and that they will stop just as soon as his larynx has stopped growing.