Bach 18 vs Yamaha HR-31-GP
The Yamaha HR-31-GP has a wider cup diameter, the Bach 18 has a larger throat opening.
The internal diameter of the cup, measured at the widest point inside the rim.
Mouthpiece A
Bach 18
• French Horn
Cup diameter16.15 mm / 0.6358 in
Best suited for
All-round versatile — balanced cup for general playing
High-volume projection — open throat for power
vs
Mouthpiece B
Yamaha HR-31-GP
• French Horn
Cup diameter17.28 mm / 0.6803 in
Best suited for
High-volume projection — open throat for power
Cup Diameter
The Yamaha HR-31-GP has a cup diameter of 17.28 mm / 0.6803 in compared to 16.15 mm / 0.6358 in on the Bach 18 — a difference of 1.13 mm / 0.0445 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.