From a reader:
a new tlm has begun in my town and some newcomers have complained about inaudibility and wanting to hear every prayer in order to better understand. those in charge have put a mic on the priest and now, all is audible; the priest does not turn it off even thru the canon. is this permissible?
secondly, most of the newcomers are used to the NO and so want to respond in a more "dialogue" fashion, but recite not only the server’s responses, but the gloria, pater noster and agnus dei as well. what is the best way to address this problem?
As far as I know, there is nothing prohibiting the use of a microphone during Mass even during the Canon. There was, even before the Council, a 1958 instruction which included a blurb about microphones. Cf. Instructio de Musica Sacra et Sacra Liturgia.
That said, there are rubrics in the older form of Mass which indicate those parts of Mass to be said silently, that is in a voice quiet enough that only those immediate servers or sacred ministers are able to hear. Using a microphone at those times of Mass would certainly violate the spirit and, it seems to me possibly the letter too, of those rubrics.
I think great care should be exercised in the older form of the Roman Rite not to confuse or compromise the distinction of the voices.
Using a microphone to make the Canon audible during a TLM just seems wrong.