I've struggled with a related issue my whole life--I'll be at a gathering, trying to jump in on a conversation, not getting noticed, and eventually I'll either just end up saying something like "HOLD ON, I have something to add," or (in the case of family gatherings) my mom will notice me getting red in the face and jump in in a less-awkward fashion that lets me be noticed. I can "project" just fine--I was drum major of my high school marching band --but there's just something about the quality of my voice in group conversation that just doesn't carry. It's very strange. However, whereas I have trouble getting (and keeping) people's attention in conversation, it sounds like people are *listening* to you already, they're just not *understanding* you. Am I interpreting your troubles correctly?

Do you speak fairly quickly? I'm a graduate student in audiology so I work regularly with individuals with hearing loss, and one of the things we always tell people when giving advice on how to improve communication is to ask conversation partners to speak more slowly, not more loudly. One doesn't need to speak exaggeratedly slow, but slowing down just a tiny bit subconsciously forces clearer (ie more enunciated) speech. It also helps if you can face the person(s) you're speaking to, and not obstruct their view of your face. Even those of us who hear perfectly well use cues from facial expression and the shape of each other's lips to improve understanding all the time without even thinking of it.

I'm no expert on voice issues--I'd defer to my counterparts on the speech-language pathology side of the field for that --but those are the things that come to mind that might help improve communication, from my experience. Noisy restaurants and such are challenging environments even for folks with normal hearing.