The "B" tone chamber will give a little more brilliance (better for using with most bands).FACINGS
Facing (3, 5, or 7): The facing is determined by the distance from the tip of the reed to where it first touches the mouthpiece. The bigger the facing number, the farther back the reed goes before actually touching the mouthpiece. Changing the facing of the mouthpiece will generally change the volume of the instrument. With a shorter facing (3), less of the reed is vibrating, so the instrument will tend to be quieter, with a longer facing (7), more of the reed is vibrating, so the instrument will tend to be louder.