Bach 11½A vs Bach 9A
The Bach 9A has a wider cup diameter.
The internal diameter of the cup, measured at the widest point inside the rim.
Mouthpiece A
Bach 11½A
• Cornet
Cup diameter15.65 mm / 0.6161 in
vs
Mouthpiece B
Bach 9A
• Cornet
Cup diameter16.05 mm / 0.6319 in
Cup Diameter
The Bach 9A has a cup diameter of 16.05 mm / 0.6319 in compared to 15.65 mm / 0.6161 in on the Bach 11½A — a difference of 0.40 mm / 0.0157 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.