Bach 18 vs Bach 20C
The Bach 18 has a wider cup diameter, the Bach 18 features a deeper cup.
The internal diameter of the cup, measured at the widest point inside the rim.
Mouthpiece A
Bach 18
• Cornet
Cup diameter15.10 mm / 0.5945 in
vs
Mouthpiece B
Bach 20C
• Cornet
Cup diameter15.00 mm / 0.5906 in
Cup Diameter
The Bach 18 has a cup diameter of 15.10 mm / 0.5945 in compared to 15.00 mm / 0.5906 in on the Bach 20C — 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.