Bach 18 vs Bach 20C
The Bach 18 has a wider cup diameter, the Bach 18 features a deeper cup.
Mouthpiece A
Bach 18
• Cornet
Cup diameter15.10 mm / 0.5945 in
Cup depthVery deep
Rim width—
Throat diameter3.66 mm / 0.1441 in
Backbore—
Finish—
Material—
vs
Mouthpiece B
Bach 20C
• Cornet
Cup diameter15.00 mm / 0.5906 in
Cup depthMedium
Rim width—
Throat diameter3.66 mm / 0.1441 in
Backbore—
Finish—
Material—
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.
Cup Depth
The Bach 18 has a very deep cup while the Bach 20C has a medium cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Throat Diameter
Throat diameters are essentially identical at 3.66 mm / 0.1441 in, 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.