Is it obligatory for those led in prayer (ma'mumeen) to raise their voices when saying "Ameen" behind the Imam during the Qunut supplication in times of calamity, or is it sufficient to say it silently? And is the Imam entitled to reprimand them for not raising their voices in doing so?

The jurists differed on the manner in which the worshipper behind the Imam says 'Ameen' during the 'Qunut al-Nawazil' (Qunut of Calamities). The Hanafis held that there is no 'Ameen' in 'Qunut al-Nawazil' unless the Imam recites it audibly. The Shafi'is and Hanbalis, on the other hand, were of the view that it should be recited audibly. As for the Malikis, they do not legislate 'Qunut al-Nawazil' in the first place. If the Imam recites the Qunut audibly, it is legislated for the worshipper behind him to say 'Ameen' audibly, without exaggeration that contradicts devotion. Saying 'Ameen' audibly is recommended, not obligatory.