Should Takbir Tahrima be said loudly?

Bismillah. Alhamdulillahi rabbil-'alamin was-Salatu was-Salam 'ala Sayyidil-Mursalin wa 'ala 'Alihi wa Sahbihi Ajma'in. ---------- **Takbir Tahrima** is a fard (obligatory) rukn of Salah. **But should it be said loudly? Or can it be said just by whispering (with very low voice) or silently (quietly)?** For both "yes" and no "answer" I need proof. **In case of "yes", what do dumb or deaf people do?** ---------- **Update** Special case that I am concerned with is that **if Takbeer is said quietly (without making any sound) then Salah is not accepted.** I'd like to know if this claim has base for. The concern comes from the fact that **Takbir Tahrima** is fard (obligatory) rukn of Salah.