How to distinguish speaker (person) from speaker (thing, loudspeaker) without using the word loudspeaker?

I would suggest that a different idea rather than "reduce to a tiny loudspeaker" be implemented, because that is pretty unidiomatic.

An option that makes sense to me and still conveys the idea of a person being lost/ignored in a conference room full of people (the exact grammar may not fit with the larger context but the important thing is the idiom):

You are/become just background music in a conference full of people

Other idioms that involve being ignored in a room full of people include "becoming furniture" or "being wall art", but background music emphasizes that the "You" is still making noise and trying to be heard.

EDIT

After realizing that OP means the person speaking is reduced to a disembodied voice passing through a loudspeaker, and not a full person, here is my updated suggestion.

Just say "voice"

You are/become just a voice in a conference full of people

That will most likely be understood as the sound of someone talking before anything else