Bach 2½C vs Bach 9B
The Bach 2½C has a wider cup diameter, the Bach 9B features a deeper cup.
The internal diameter of the cup, measured at the widest point inside the rim.
Mouthpiece A
Bach 2½C
• Cornet
Cup diameter16.40 mm / 0.6457 in
Best suited for
All-round versatile — balanced cup for general playing
vs
Mouthpiece B
Bach 9B
• Cornet
Cup diameter16.05 mm / 0.6319 in
Cup Diameter
The Bach 2½C has a cup diameter of 16.40 mm / 0.6457 in compared to 16.05 mm / 0.6319 in on the Bach 9B — a difference of 0.35 mm / 0.0138 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Which is better?
Neither mouthpiece clearly dominates the other — the right choice depends on your embouchure, playing style, and the sound you're after. Try both if possible.