Bach 18C vs Bach 2½C
The Bach 2½C has a wider cup diameter.
Mouthpiece A
Bach 18C
• Cornet
Cup diameter15.10 mm
Cup depthMedium
Rim width—
Throat diameter3.66 mm
Backbore—
Finish—
Material—
vs
Mouthpiece B
Bach 2½C
• Cornet
Cup diameter16.40 mm
Cup depthMedium
Rim width—
Throat diameter3.66 mm
Backbore—
Finish—
Material—
Best suited for
All-round versatile — balanced cup for general playing
Cup Diameter
The Bach 2½C has a cup diameter of 16.40 mm compared to 15.10 mm on the Bach 18C — a difference of +1.30 mm. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
Both mouthpieces share a medium cup depth, so the sound character from depth alone will be very similar.
Throat Diameter
Throat diameters are essentially identical at 3.66 mm, so resistance feel will be comparable.
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.