Some people say that the jawf is the chest area, whereas your book says the jawf is the empty space in the mouth and throat.

Question
Assalaamu alaykum.  Ahsan Allaahu ilaykum.  Some people say that the jawf is the chest area, whereas your book says the jawf is the empty space in the mouth and throat.  Is the teacher who teaches the first statement incorrect?

Answer
Wa alaikum assalaam wa rahmatullahi wa barakatuh.  Baarak Allahu feekum.
We know of no text from the early scholars or even modern scholars of tajweed which states the jawf is in the chest area.  Human sounds of speech are produced by vibration of the vocal chords which is in the throat, and then the the sound is shaped from above that by the position of the tongue, teeth, mouth, or empty space (not a specific place).  And Allah knows best.