Don't mean to hijack the thread. I first tried the tiny RS lapel mic but didn't have much luck with the powered omni mic. I returned it and got the RS uni boom mic and still had feedback problems. Then I read Chris' post. Sooo...
Ok, just in case anyone is interested... Any sound escaping from the front of the speaker (if you have internally mounted speakers) will cause feedback in your mic - be it uni or omnidirectional. I'm using standard RS mini speakers:
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which are mounted inside the helmet behind the aerator bulge. Like I said in my previous post, I had mounted these bad boys inside spray paint lids, first with some foam behind 'em to reduce feedback (which didn't work), then with some denser foam (nope), then with some Dynamat - both inside the lids and out (SQUEAL!). That's when I grabbed some adhesive putty, like Blu-Tack, but whatever is available in your area will do. I used the Duck brand stuff (which happens to be blue), but the white Scotch stuff will work just as well. Anyway, I placed the speakers flat against the areator bulge/hole and puttied all around the speaker, making sure I filled all the holes. Result - no feedback at all. Even with the RS amp cranked to the max! I then spread some more putty around the speaker, laid some Dynamat down in the base of the spray paint caps, trimmed the caps down drastically (so I could get my big grape in my lid ), and hot glued them onto the speaker/putty assembly.
I'll post some crappy cell-phone pics this afternoon if anyone is interested. No in-progress shots, just nearly-done shots.