I have the MiniRingtone program and tried everything from +10 to +22 for my music ringtones. Once they got loud enough for me to use as a ringtone without fear of missing every incoming call they had too much distortion. Maybe I wasn't using it correctly.
I downloaded the "Classic" ringtone and found that to be loud enough to hear under just about any condition, including when my 8830 was in my locked car (with windows up) and I was about 12-feet away. In fact, my 8830 now rings louder than just about any other phone I've owned.
Robert7200, thanks for the information, but that's been posted several times. All it does is set the default Loud profile to loud (you're right, one would think that would be the default in the first place), but even the loud "Loud" profile isn't loud enough for many of us. The problem is that the 8830's ringer volume just isn't loud enough to be heard under normal everyday use (at least IMO). I hope it works for you, maybe you were lucky enough to get an 8830 with a decent ringer.
Here is the link for the "Classic" ringer in case anyone is interested. After using it for awhile, now I actually prefer a "ring" to a "tune" when I get a call.