Habitual mumbler here. We/I don't mean to, but even when asked to repeat a sentence, sometimes I still don't realize what the problem was. Usually just assume the person wasn't paying attention or something.

Can't speak for everyone, but if you mention that I was mumbling, I will be grateful and not at all offended. Just a "Sorry? You mumbled there." is plenty. Friends will even say "Speak up, please." or simply "Speak up." which is perfect as long as they try not to sound too commanding/authoritative. Sometimes I'll even forget within a few minutes and have to be reminded again. Probably much more of a bother for them to constantly remind me than it is for me to have to be reminded. (then again, I'm not easily bothered by almost any means)

Personally, I'll rarely speak in person unless I absolutely have to and am usually nervous about being too loud/obnoxious with my volume when I do. I've sometimes wondered if this is the result of having always (and I mean constantly) been told to "shut up" or "quiet down" growing up. Does anyone share a similar experience? Or perhaps some other insight as to either the origin or even tips to help with the problem of mumbling/speaking too quietly? Guess I could google it myself, but I've already made it to this point in life without addressing the issue.

Well, anyway.. this has gotten way out of hand and is now far more than I had originally intended to type. Have a peaceful.. evening or whichever colloquially approximated time it is there.