The Vibration of Sound
Qalqalah means "vibration" or "echo". It is a Tajweed rule applied when specific letters have a Sukoon (are silent) or when stopping on them. Because these letter sounds can get "trapped" in the articulation point, we release them with a slight echo to make them audible.
The 5 Qalqalah Letters
Memorize them with the phrase:
"Qutb Jad" (قُطْبُ جَد)
قطبجد
Levels of Qalqalah
The strength of the echo depends on the position of the letter:
Weakest
Qalqalah Sughra
When the letter is in the middle of a word. The echo is quick and subtle.
Ex: Yadkhuloon
Medium
Qalqalah Kubra
When stopping at the end of a word (without Shaddah). The echo is clearer.
Ex: Falaq
Strongest
Qalqalah Akbar
When stopping at the end of a word that has a Shaddah. The echo is delayed and powerful.
Ex: Al-Hajj