Bach 12C vs Bach 18C
The Bach 12C 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 18C
• Cornet
Cup diameter15.10 mm / 0.5945 in
Cup Diameter
The Bach 12C has a cup diameter of 15.20 mm / 0.5984 in compared to 15.10 mm / 0.5945 in on the Bach 18C — a difference of 0.10 mm / 0.0039 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.