Answer: According to the five parts of the spiritual Kli, Keter, Hochma, Bina, Zeir Anpin, and Malchut, we distinguish five groups of sounds: guttural, lingual, palatal (from the palate), from the cheeks, and lips. In this manner, it is possible not only to write the letters but also to express them.
The same thing also exists regarding musical notes, the colors of the rainbow, and everything that exists, since all of them are rooted in the five parts of the spiritual Kli.
Everything in our world that people work with is included in this system, just like our five senses: sight, hearing, smell, taste, and touch.
From the Kabbalah Lesson in Russian 7/17/16