It is wajib for imam to make loud qirah in both the rakahs of Fajr and in the first two rakahs of Maghrib and Isha – whether he is performing ada (in time) or qaza (after time) and in all the rakahs of Jumuah, Eidain, tarawih and the witr of Ramadan while offering with jamah. The muqtadi cannot recite behind the imam in any salah whether it is silent salah or loud salah, as the qirah is forbidden behind the imam. However, if a person offers the above mentioned salah alone provided jamah is not a condition for that salah, as the salah in which jamah is a condition such as Jumuah and Eidain these salah are not valid alone without a jamah, then jahri (loud) qirah is not wajib in it. However, a slow jahr is lawful rather it is better provided it does not create problem for others; otherwise he should stand away from people and offer the salah. For more details and proofs see I’la al-Sunan (4: 3-17 p. Idaratul Quran al-Uloom al-Islamia, Karachi, Pakistan) and al-Dur al-Mukhtar and Shami (Kitab al-Salah, Bab Sifah al-salah, Fazlun Fil Qirah 2:249-251, p. Maktaba Zakaria Deoband).
Allah knows Best!
Darul Uloom Deoband