Question: The adhan is called out from a central mosque. Besides, people start to place TV screens on the walls of some mosques so that followers can see imams. Is it not bid'at?
ANSWER
Similar implementation has been initiated in India, too. It leaves us with an impression that there is preparation for elimination of imams of small mosques in order for people to follow the imams in central mosques, as we see in India.

We have heard that in India the Wahhabis performed salat without an imam in some mosques. We have learnt that these mosques were connected to the central mosque and the jama’at followed the imam by hearing his voice through loudspeakers. The fact that those salats performed by following the voice emitted from a loudspeaker or the image of the imam on television are not valid, is written in the the magazine Al-Mu’allim, dated Rabi’ul-awwal, 1406 [December, 1985], and published by the Indian Muslim scholars in Kerala. It is written in the book Suyufullah-il-Ajilla that it is not permissible to join a jama’at conducted through a loudspeaker by the imam. (Se'adet-i Ebediyye)

When Habib-ur-Rahman, the dean of Jamia-i Habibiyya in Pakistan, went on a pilgrimage in 1981, he saw that the Wahhabi imam was leading salat by employing the use of a loudspeaker, and therefore, he performed salats separately. As a result, he was handcuffed and imprisoned. Then he was denied the right to perform hajj and was sent to his country. (İslam Ahlakı)

Question: Is it permissible to say "Amin" to the du'a of a person relayed on a TV screen as it is not his actual voice?
ANSWER
Yes, one can say "Amin" to it. The loudspeaker acts as proxy for the speaker, and it transmits the speaker's voice to us. It is like a deputy. There is nothing wrong with arranging for a deputy to do a task. Just as one is allowed to send one's regards or to make du'a through someone else, so one is allowed to send one's regards or to make du'a through devices having loudspeakers. We can return the regards sent by these means or say "Amin" to the du'a made by these means.
The case is different as for salat. You cannot arrange for someone else to perform salat for you. The sound emitted from a loudspeaker is not the actual voice of the speaker. It is only likeness. That is, it is the voice of the deputy. It converts into some other sound. It is not permissible to follow this reconstructed voice in salat. Moreover, it is bid'at. It is permissible to make someone do something by proxy in all activities, such as preaching, teaching, except recitation of adhan and the Qur'an or performing salat.

Question: As musical instruments and any type of instrument that emits sound are called mizmar in the book Se'adet-i Ebediyye, are televisions and loudspeakers considered mizmar, too?
ANSWER
Yes, they are considered mizmar, too. It is written in the same book:

Any instrument that is used to produce sound is called mizmar. A drum, a tambourine, a woodwind instrument such as a reed flute, a violin, a lute, a loudspeaker, a tape recorder, and a television set are a mizmar each. (Se'adet-i Ebediyye)

Mizmar refers to any type of musical instrument and a whistle. The loudspeaker is a mizmar, too. (İslam Ahlakı)

Instruments that produce sounds for pleasure, such as drums, tambourines, cymbals, reeds, flutes, loudspeakers, are all musical instruments. A musical instrument does not produce sound by itself. They have to be used so as to produce sound, i.e., with the drum you have to strike the tightly stretched skin with a stick, with the reed you have to blow, and with the loudspeaker you have to articulate sounds. The sound that comes out from them is their own production. (Se'adet-i Ebediyye)

It is haram to recite the Qur'an al-karim and to perform other duties [such as adhan, iqamat, and imamhood] by employing the use of musical instruments. It is not permissible for a fasiq (a person who sins openly) to call out the adhan even in a pure and respectable manner. Similarly, as the loudspeaker is used to spread sinful songs and women voices, it is not permissible to call out the adhan by using it, even if the voice were not converted into some other sound, because the act of worship cannot be changed. (İslam Ahlakı)