Loudspeaker/Intercom/P.A. effect?

how would I go about making a recorded voice sound like it is over an intercom or P.A.? like those in a place where someone over the loudspeaker would say “attention all participants…” yada yada.

Well I would start with a fairly narrow band equalization, the “telephone” preset is probably a good starting point.
Add a bit of distortion – The built-in hard limiter or the “broadcast limiter II” might be good choices to play with.
Finally add reverb to whatever degree fits your desire.

Also see “megaphone”.

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