Rambam, Hilchot Tefilah 12:11 talks about the מתורגמן, a translator who would translate the Torah into Aramaic during the reading. He says that neither the reader nor the translator may be louder than the other one.
He writes this in the context of an actual translator, but i remember learning that this also applies to another מתורגמן, one who simply repeats what the lecturer says.
If this מתורגמן is only repeating what the lecturer says, then what's the point? He can't even say it louder than the original speaker!