i am thinking of buying one of these mouthpieces.
i live in FREEZING COLD michigan.
it is not suppose to get to 20 degrees farienheit until next tuesday here, i rreally hate living here sometimes, so i think these mouthpieces would be good for me because it won't get cold.
so my question is what size kelly mouthpice is compatiable with my yamaha 9C4?

I've been meaning to look up the equivalents of Yamaha mouthpieces. I have no I idea if a yamaha 9C4 mouthpiece is a beginner or pro mouthpiece but I can tell you about the C system. A 7C is given to most beginners. After they can play fairly well most will upgrade to a 3C mouthpiece, its a bit shallower and allows you to reach higher notes a little easier.Its pretty good if your playing in the range of a C below the staff to a C above the staff and is somewhat standard in high school bands. A 1C is about the shallowest mouthpiece you can get. In my experience its been a little tough to play notes below a C in the staff and not make them sound thin and airy with the 1C, but you can breeze over those high notes though. Plastic is a good choice for playing up there, the metal doesnt freeze to your lips. Happened to my friend once, fricken hilarious.

hey,

First off i want to give my full endorsement toward kelly mouthpieces. I live in NE Ohio, which certainly has it's fair share (and more) of freezing days. I've used kelly mouthpieces through freezing cold parades and could still reach well beyond double high C. As far as Yamaha's goofy mouthpiece naming system, i am including a link to Yamaha's website that gives equivalence charts from Yamaha to bach, etc.

http://www.yamaha.com/band/accessories/mouthpiececomps.htm#

Hope this helps and good luck!

i play cornet and trumpet and i use kelly mouthpieces on both (im gonna change to a metal one on trumpet soon) i think there great, especially for playing carols as the temperature never changes that can also be a bad thing though as you don't know when your properly wormed up.