New are also the letters in the 2. Besides the broad slash they are the left halves of the signs in the 4.
Vowels are flat, consonants high.
Humming consonants consist of straight vertical lines. So the asymmetrical signs, consisting of 1 straight line each, represent the 4 directions, with wich signs can begin, and simultaneously the 4 sound groups. There surely are better ways to associate these sounds to these signs. But then this extended system was not more compatible to the simple system with only 12 letters. But it seems to be better to give some phonetic training to some people than always to handle optically unsatisfactory ideograms.