Bach 12C vs Bach 2½C
The Bach 2½C has a wider cup diameter.
The internal diameter of the cup, measured at the widest point inside the rim.
Mouthpiece A
Bach 12C
• Cornet
Cup diameter15.20 mm / 0.5984 in
vs
Mouthpiece B
Bach 2½C
• Cornet
Cup diameter16.40 mm / 0.6457 in
Best suited for
All-round versatile — balanced cup for general playing
Cup Diameter
The Bach 2½C has a cup diameter of 16.40 mm / 0.6457 in compared to 15.20 mm / 0.5984 in on the Bach 12C — a difference of 1.20 mm / 0.0472 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.