The Qalqalah 
. If we attempt to say one of these five qalqalah letters with a sukoon( ق ط ب ج د ), we would find that the articulation point closes completely, and that it causes an annoyance in the articulation mechanism. This is due to imprisonment of the sound behind the articulation point. When these same five letters have vowels, we do not find this annoyance because voweled letters are pronounced parting of the two components of the articulating parts.