The ruling on repeating the imam's takbir behind him in prayer

Q: What is the ruling on repeating the imam's takbir behind him in prayer with a loud voice, given that everyone can hear the imam's takbir and his praise of Allah?

A: If the congregation can hear the imam's voice and it is not hidden from them, there is no need for the call to prayer. However, if it may be hidden from some of them, such as the rear rows, then it is recommended to make the call. The Prophet (peace and blessings be upon him) once prayed while ill, and his voice was weak, so al-Ṣiddiq (may Allah be pleased with him) would make the call on his behalf (peace and blessings be upon him). There is nothing wrong with this.
If repeating the takbir is needed due to the size of the mosque and the large number of people in the congregation, or because the imam's voice is weak due to illness or otherwise, then some of the congregation should repeat it. But if the voice is clear to everyone and not hidden from anyone at the edges, and it is known that everyone hears it, then there is no need to repeat it, and it is not prescribed.