During the antiquity, different versions of the phonetic picture-writing have been used. Often the difference was only an other attachment of sounds to the signs, e.g. to exchange the spirants for the plosives, and vice versa. Not to disturb the reader, we present only 1 version in this article. Here again the table with the 12 letters. If you touch your larynx, or put a small finger into an ear, and speak a humming sound, you feel vibrations.
Vowels also hum.
Humming sounds are written by straight lines, parallel to a co- ordinate axis. Not humming sounds are written by other lines. They symbolize emitting, broadening air. Then air is emitted explosively. By turning down the one, you get the other one.