Hi troopers, in the struggle of squeezing my ROM/FX and micro speakers for maximum volume I found out that what is missing is a resonant chamber to pump it up. You can try with yours: close partially the mic tip opening with your finger and you hear the bump in volume.
What I did is cut a small strip of thin clear acrylic and install it just behind the speaker grill, like this:
This creates a small resonance chamber and the side gaps let the sound out. This increases some frequencies and focuses the sound on mids, making the voice more "annoying", but definitely more intelligible and loud.
Since the strip is clear, once installed it's almost invisible, here's the result:
Try different sizes until you find the best frequency and volume bump.
I suggest these speakers paired with Stomper Hovies for best results.