Ha! This is the second time in two days I found myself and someone else going down the exact same path.
In my case, I'm mounting a small microphone inside the mask, and in the bellows hiding batteries and speakers. The voice modulation I'm tweaking now, but hoping to accomplish with an Arduino, but I may upgrade the hardware.
Here a start for anyone interested.
The Adafruit Wave Shield for Arduino.
When I'm done, I'll post how I did it and what I used. I'll share project details too. This may come a little later as I'm moving this weekend, but I'll circle back and let you know.
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Though if I can find a way to mount them in my filters that might work far better.
As it is I have filters that are a little too big. Maybe I can look at that as an asset.