Answer
(Fatwa: 1431/1053/D=1433)
If the voice of the imam is not reaching to the musallis then it is lawful to use loudspeaker though it is better not to use it. If loudspeaker is installed then it is necessary that the voice is up to the area where the muqtadi are present. It is makrooh to spread the voice more than that area or outside. And in case the general public feels problem then it is utterly undesirable. It is necessary to avoid it.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband